LTC2983 Multi-Sensor High Accuracy Digital Temperature Measurement System DESCRIPTION FEATURES Directly Digitize RTDs, Thermocouples, Thermistors and Diodes nn Single 2.85V to 5.25V Supply nn Results Reported in °C or °F nn 20 Flexible Inputs Allow Interchanging Sensors nn Automatic Thermocouple Cold Junction Compensation nn Built-In Standard and User-Programmable Coefficients for Thermocouples, RTDs and Thermistors nn Configurable 2-, 3- or 4-Wire RTD Configurations nn Measures Negative Thermocouple Voltages nn Automatic Burn Out, Short-Circuit and Fault Detection nn Buffered Inputs Allow External Protection nn Simultaneous 50Hz/60Hz Rejection nn Includes 15ppm/°C (Max) Reference (I-Grade) nn APPLICATIONS Direct Thermocouple Measurements Direct RTD Measurements nn Direct Thermistor Measurements nn Custom Sensor Applications nn nn The LTC®2983 measures a wide variety of temperature sensors and digitally outputs the result, in °C or °F, with 0.1°C accuracy and 0.001°C resolution. The LTC2983 can measure the temperature of virtually all standard (type B, E, J, K, N, S, R, T) or custom thermocouples, automatically compensate for cold junction temperatures and linearize the results. The device can also measure temperature with standard 2-, 3- or 4-wire RTDs, thermistors and diodes. It has 20 reconfigurable analog inputs enabling many sensor connections and configuration options. The LTC2983 includes excitation current sources and fault detection circuitry appropriate for each type of temperature sensor. The LTC2983 allows direct interfacing to ground referenced sensors without the need for level shifters, negative supply voltages, or external amplifiers. All signals are buffered and simultaneously digitized with three high accuracy, 24-bit ∆∑ ADCs, driven by an internal 15ppm/°C (maximum) reference. L, LT, LTC, LTM, Linear Technology and the Linear logo are registered trademarks of Linear Technology Corporation. All other trademarks are the property of their respective owners. Patents Pending TYPICAL APPLICATION Thermocouple Measurement with Automatic Cold Junction Compensation Typical Temperature Error Contribution 2.85V TO 5.25V 1k 0.5 LTC2983 1k RSENSE 2k 0.4 0.3 24-BIT ∆∑ ADC 0.2 LINEARIZATION/ FAULT DETECTION 24-BIT ∆∑ ADC ERROR (°C) 0.1µF SPI INTERFACE 2 0 –0.1 –0.3 3904 DIODE RTD –0.4 –0.5 –200 0 4 3 PT-100 RTD THERMOCOUPLE 0.1 –0.2 °C/°F THERMISTOR 200 400 600 800 1000 1200 1400 TEMPERATURE (°C) 2983 TA01b 24-BIT ∆∑ ADC 1 VREF (10ppm/°C) 2983 TA01a 2983fc For more information www.linear.com/LTC2983 1 LTC2983 TABLE OF CONTENTS Features............................................................................................................................. 1 Applications........................................................................................................................ 1 Typical Application ................................................................................................................ 1 Description......................................................................................................................... 1 Absolute Maximum Ratings...................................................................................................... 3 Order Information.................................................................................................................. 3 Complete System Electrical Characteristics................................................................................... 3 Pin Configuration.................................................................................................................. 3 ADC Electrical Characteristics................................................................................................... 4 Reference Electrical Characteristics............................................................................................ 4 Digital Inputs and Digital Outputs............................................................................................... 5 Typical Performance Characteristics........................................................................................... 6 Pin Functions....................................................................................................................... 9 Block Diagram.....................................................................................................................10 Test Circuits.......................................................................................................................11 Timing Diagram...................................................................................................................11 Overview...........................................................................................................................12 Applications Information........................................................................................................16 Thermocouple Measurements............................................................................................................................... 21 Diode Measurements............................................................................................................................................. 24 RTD Measurements............................................................................................................................................... 28 Thermistor Measurements..................................................................................................................................... 43 Direct ADC Measurements..................................................................................................................................... 55 Supplemental Information.......................................................................................................55 Fault Protection and Anti-Aliasing.......................................................................................................................... 57 2- and 3-Cycle Conversion Modes......................................................................................................................... 57 Running Conversions Consecutively on Multiple Channels.................................................................................... 58 MUX Configuration Delay....................................................................................................................................... 58 Global Configuration Register................................................................................................................................ 59 Custom Thermocouples..........................................................................................................59 Custom RTDs......................................................................................................................62 Custom Thermistors..............................................................................................................65 Package Description.............................................................................................................70 Revision History..................................................................................................................71 Typical Application...............................................................................................................72 Related Parts......................................................................................................................72 2 2983fc For more information www.linear.com/LTC2983 LTC2983 ABSOLUTE MAXIMUM RATINGS PIN CONFIGURATION (Notes 1, 2) Supply Voltage (VDD).................................... –0.3V to 6V Analog Input Pins (CH1 to CH20, COM).................................. –0.3V to (VDD + 0.3V) Input Current (CH1 to CH20, COM)....................... ±15mA Digital Inputs (CS, SDI, SCK, RESET)................................. –0.3V to (VDD + 0.3V) Digital Outputs (SDO, INTERRUPT). –0.3V to (VDD + 0.3V) VREFP......................................................... –0.3V to 2.8V Q1, Q2, Q3, LDO, VREFOUT, VREF_BVP (Note 17) Reference Short-Circuit Duration...................... Indefinite Operating Temperature Range LTC2983C..................................................0ºC to 70ºC LTC2983I.............................................. –40ºC to 85ºC LTC2983H............................................–40ºC to 125ºC 12 11 10 9 8 7 6 5 4 3 2 1 GND VREF_BYP NC GND VDD GND VDD GND VDD GND VDD GND TOP VIEW 13 14 15 16 17 18 19 20 21 22 23 24 48 47 46 45 44 43 42 41 40 39 38 37 Q1 Q2 Q3 VDD GND LDO RESET CS SDI SDO SCK INTERRUPT CH10 CH11 CH12 CH13 CH14 CH15 CH16 CH17 CH18 CH19 CH20 COM 25 26 27 28 29 30 31 32 33 34 35 36 VREFOUT VREFP GND CH1 CH2 CH3 CH4 CH5 CH6 CH7 CH8 CH9 LX PACKAGE 48-LEAD (7mm × 7mm) PLASTIC LQFP TJMAX = 150°C, θJA = 57°C/W ORDER INFORMATION LEAD FREE FINISH TRAY PART MARKING* PACKAGE DESCRIPTION TEMPERATURE RANGE LTC2983CLX#PBF LTC2983CLX#PBF LTC2983LX 48-Lead (7mm × 7mm) LQFP 0°C to 70°C LTC2983ILX#PBF LTC2983ILX#PBF LTC2983LX 48-Lead (7mm × 7mm) LQFP –40°C to 85°C LTC2983HLX#PBF LTC2983HLX#PBF LTC2983LX 48-Lead (7mm × 7mm) LQFP –40°C to 125°C Consult LTC Marketing for parts specified with wider operating temperature ranges. *The temperature grade is identified by a label on the shipping container. For more information on lead free part marking, go to: http://www.linear.com/leadfree/ COMPLETE SYSTEM ELECTRICAL CHARACTERISTICS The l denotes the specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25°C. PARAMETER CONDITIONS MIN Supply Voltage l Supply Current l Sleep Current TYP 2.85 5.25 15 25 l MAX UNITS V 20 mA 60 µA VDD – 0.3 V Input Range All Analog Input Channels l –0.05 Output Rate Two Conversion Cycle Mode (Notes 6, 9) l 150 164 170 ms Output Rate Three Conversion Cycle Mode (Notes 6, 9) l 225 246 255 ms Input Common Mode Rejection 50Hz/60Hz (Note 4) l 120 dB Input Normal Mode Rejection 60Hz (Notes 4, 7) l 120 dB 2983fc For more information www.linear.com/LTC2983 3 LTC2983 COMPLETE SYSTEM ELECTRICAL CHARACTERISTICS The l denotes the specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25°C. PARAMETER CONDITIONS Input Normal Mode Rejection 50Hz (Notes 4, 8) l MIN 120 Input Normal Mode Rejection 50Hz/60Hz (Notes 4, 6, 9) l 75 Power-On Reset Threshold TYP MAX UNITS dB dB 2.25 V Analog Power-Up (Note 11) l 100 ms Digital Initialization (Note 12) l 100 ms ADC ELECTRICAL CHARACTERISTICS The l denotes the specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25°C. PARAMETER CONDITIONS Resolution (No Missing Codes) –FS ≤ VIN ≤ + FS l Integral Nonlinearity VIN(CM) = 1.25V (Note 15) l 2 30 ppm of VREF l 0.5 2 µV 10 Offset Error MIN Offset Error Drift (Note 4) l Positive Full-Scale Error (Notes 3, 15) l Positive Full-Scale Drift (Notes 3, 15) l Input Leakage (Note 18) H-Grade l l TYP MAX 24 UNITS Bits 0.1 20 nV/°C 100 ppm of VREF 0.5 ppm of VREF/°C 1 10 nA nA Negative Full-Scale Error (Notes 3, 15) l 100 ppm of VREF Negative Full-Scale Drift (Notes 3, 15) l 0.1 0.5 ppm of VREF/°C Input Referred Noise (Note 5) H-Grade l l 0.8 1.5 2.0 µVRMS µVRMS Common Mode Input Range l –0.05 (Note 16) l –25 RTD Excitation Current Matching Continuously Calibrated l Thermistor Excitation Current (Note 16) l RTD Excitation Current Table 30 VDD – 0.3 V 25 % Error within Noise Level of ADC –37.5 Table 53 37.5 % REFERENCE ELECTRICAL CHARACTERISTICS The l denotes the specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25°C. PARAMETER CONDITIONS MIN TYP Output Voltage VREFOUT (Note 10) I-Grade, H-Grade l 3 15 ppm/°C Output Voltage Temperature Coefficient C-Grade l 3 20 ppm/°C Load Regulation Output Voltage Noise Output Short-Circuit Current Turn-On Time 4 V l 10 ppm/V IOUT(SOURCE) = 100µA l 5 mV/mA IOUT(SINK) = 100µA l 5 mV/mA 0.1Hz ≤ f ≤ 10Hz 4 µVP-P 10Hz ≤ f ≤ 1kHz 4.5 µVP-P Short VREFOUT to GND 40 mA Short VREFOUT to VDD 30 mA 0.1% Setting, CLOAD = 1µF 115 µs 60 ppm/√khr 30 70 ppm ppm Long Term Drift of Output Voltage (Note 13) Hysteresis (Note 14) 2.51 UNITS Output Voltage Temperature Coefficient Line Regulation 2.49 MAX ∆T = 0°C to 70°C ∆T = –40°C to 85°C 2983fc For more information www.linear.com/LTC2983 LTC2983 DIGITAL INPUTS AND DIGITAL OUTPUTS The l denotes the specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25°C. SYMBOL PARAMETER CONDITIONS MIN TYP MAX External SCK Frequency Range l 0 External SCK LOW Period l 250 250 0 200 200 External SCK HIGH Period l t1 CS↓ to SDO Valid l t2 CS↑ to SDO Hi-Z l 0 t3 CS↓ to SCK↑ l 100 t4 SCK↓ to SDO Valid l 2 UNITS MHz ns ns ns ns ns 225 ns t5 SDO Hold After SCK↓ l 10 ns t6 SDI Setup Before SCK↑ l 100 ns t7 SDI HOLD After SCK↑ l 100 ns VDD – 0.5 High Level Input Voltage CS, SDI, SCK, RESET l Low Level Input Voltage CS, SDI, SCK, RESET l Digital Input Current CS, SDI, SCK, RESET l Digital Input Capacitance CS, SDI, SCK, RESET LOW Level Output Voltage (SDO, INTERRUPT) IO = –800µA l High Level Output Voltage (SDO, INTERRUPT) IO = 1.6mA l VDD – 0.5 l –10 Hi-Z Output Leakage (SDO) Note 1: Stresses beyond those listed under Absolute Maximum Ratings may cause permanent damage to the device. Exposure to any Absolute Maximum Rating condition for extended periods may affect device reliability and lifetime. Note 2: All voltage values are with respect to GND. Note 3: Full scale ADC error. Measurements do not include reference error. Note 4: Guaranteed by design, not subject to test. Note 5: The input referred noise includes the contribution of internal calibration operations. Note 6: MUX configuration delay = default 1ms Note 7: Global configuration set to 60Hz rejection. Note 8: Global configuration set to 50Hz rejection. Note 9: Global configuration default 50Hz/60Hz rejection. Note 10: The exact value of VREF is stored in the LTC2983 and used for all measurement calculations. Temperature coefficient is measured by dividing the maximum change in output voltage by the specified temperature range. Note 11: Analog power-up. Command status register inaccessible during this time. Note 12: Digital initialization. Begins at the conclusion of Analog PowerUp. Command status register is 0 × 80 at the beginning of digital initialization and 0 × 40 at the conclusion. Note 13: Long-term stability typically has a logarithmic characteristic and therefore, changes after 1000 hours tend to be much smaller than before that time. Total drift in the second thousand hours is normally less V –10 0.5 V 10 µA 10 pF 0.4 V 10 µA V than one third that of the first thousand hours with a continuing trend toward reduced drift with time. Long-term stability will also be affected by differential stresses between the IC and the board material created during board assembly. Note 14: Hysteresis in output voltage is created by package stress that differs depending on whether the IC was previously at a higher or lower temperature. Output voltage is always measured at 25°C, but the IC is cycled to the hot or cold temperature limit before successive measurements. Hysteresis measures the maximum output change for the averages of three hot or cold temperature cycles. For instruments that are stored at well controlled temperatures (within 20 or 30 degrees of operational temperature), it is usually not a dominant error source. Typical hysteresis is the worst-case of 25°C to cold to 25°C or 25°C to hot to 25°C, preconditioned by one thermal cycle. Note 15: Differential Input Range is ±VREF/2. Note 16:RTD and thermistor measurements are made ratiometrically. As a result current source excitation variation does not affect absolute accuracy. Choose an excitation current such that largest sensor or RSENSE resistance value, when driven by the nominal excitation current, will drop 1V or less. The extended ADC input range will accommodate variation in excitation current and the ratiometric calculation will negate the absolute value of the excitation current. Note 17: Do not apply voltage or current sources to these pins. They must be connected to capacitive loads only, otherwise permanent damage may occur. Note 18: Input leakage measured with VIN = –10mV and VIN = 2.5V. 2983fc For more information www.linear.com/LTC2983 5 LTC2983 TYPICAL PERFORMANCE CHARACTERISTICS Type K Thermocouple Error and RMS Noise vs Temperature 1.0 0.8 0.8 0.6 0.6 0.6 0.4 0.2 0 –0.2 –0.4 ERROR/RMS NOISE (°C) 1.0 0.8 –0.6 0.4 0.2 0 –0.2 –0.4 –0.6 –0.8 –1.0 –400 RMS NOISE ERROR –1.0 –400 0 400 800 1200 1600 THERMOCOUPLE TEMPERATURE (°C) 0.2 0 –0.2 –0.4 –0.8 –1.0 –400 0 400 800 1200 1600 THERMOCOUPLE TEMPERATURE (°C) Type S Thermocouple Error and RMS Noise vs Temperature Type T Thermocouple Error and RMS Noise vs Temperature 0.8 0.8 0.8 0.6 0.6 0.6 0 –0.2 –0.4 –0.6 ERROR/RMS NOISE (°C) 1.0 ERROR/RMS NOISE (°C) 1.0 0.2 0.4 0.2 T 0 –0.2 –0.4 –1.0 –400 RMS NOISE ERROR –0.8 –1.0 –400 0 400 800 1200 1600 2000 THERMOCOUPLE TEMPERATURE (°C) 0.4 0.2 0 –0.2 –0.4 –0.6 –0.6 –0.8 2983 G04 RMS NOISE ERROR –0.8 –1.0 –400 0 400 800 1200 1600 2000 THERMOCOUPLE TEMPERATURE (°C) Type B Thermocouple Error and RMS Noise vs Temperature 0.8 0.6 0.6 0.6 –0.2 –0.4 –1.0 –400 RMS NOISE ERROR 0 400 800 1200 THERMOCOUPLE TEMPERATURE (°C) 2983 G07 6 0.2 0 –0.2 –0.4 –0.6 –0.6 –0.8 ERROR/RMS NOISE (°C) 0.8 ERROR/RMS NOISE (°C) 1.0 0.8 0.4 –0.8 –1.0 400 600 RTD PT-1000 Error and RMS Noise vs Temperature 1.0 0 –200 0 200 400 THERMOCOUPLE TEMPERATURE (°C) 2983 G06 1.0 0.2 RMS NOISE ERROR 2983 G05 Type E Thermocouple Error and RMS Noise vs Temperature 0.4 0 400 800 1200 1600 THERMOCOUPLE TEMPERATURE (°C) 2983 G03 1.0 0.4 RMS NOISE ERROR 2983 G02 Type R Thermocouple Error and RMS Noise vs Temperature ERROR/RMS NOISE (°C) 0.4 –0.6 RMS NOISE ERROR –0.8 2983 G01 ERROR/RMS NOISE (°C) Type N Thermocouple Error and RMS Noise vs Temperature 1.0 ERROR/RMS NOISE (°C) ERROR/RMS NOISE (°C) Type J Thermocouple Error and RMS Noise vs Temperature 0.4 0.2 0 –0.2 –0.4 –0.6 RMS NOISE ERROR 800 1200 1600 2000 THERMOCOUPLE TEMPERATURE (°C) 2983 G08 –0.8 –1.0 –400 RMS NOISE ERROR 0 400 RTD TEMPERATURE (°C) 800 2983 G09 2983fc For more information www.linear.com/LTC2983 LTC2983 TYPICAL PERFORMANCE CHARACTERISTICS 1.0 1.0 0.8 0.8 0.8 0.6 0.6 0.6 0.2 0 –0.2 –0.4 –0.6 ERROR/RMS NOISE (°C) 1.0 0.4 0.4 0.2 0 –0.2 –0.4 –1.0 –400 RMS NOISE ERROR 0.2 0 –0.2 –0.4 0 400 RTD TEMPERATURE (°C) –0.6 RMS NOISE ERROR –0.8 –1.0 –400 –200 800 0 200 400 600 RTD TEMPERATURE (°C) 2983 G10 –0.8 –1.0 –100 800 1000 3k Thermistor Error vs Temperature 0.8 0.8 0.6 0.6 0.6 0.4 0.4 0.4 0.2 0.2 0.2 ERROR (°C) 0.8 ERROR (°C) 1.0 0 –0.2 300 5k Thermistor Error vs Temperature 1.0 –0.2 0 100 200 RTD TEMPERATURE (°C) 2983 G12 1.0 0 RMS NOISE ERROR 2983 G11 2.252k Thermistor Error vs Temperature 0 –0.2 –0.4 –0.4 –0.4 –0.6 –0.6 –0.6 –0.8 –0.8 –0.8 –1.0 –40 –20 0 20 40 60 80 100 120 140 THERMISTOR TEMPERATURE (°C) –1.0 –40 –20 0 20 40 60 80 100 120 140 THERMISTOR TEMPERATURE (°C) –1.0 –40 –20 0 20 40 60 80 100 120 140 THERMISTOR TEMPERATURE (°C) 2983 G19 2983 G20 2983 G21 30k Thermistor Error vs Temperature 10k Thermistor Error vs Temperature YSI-400 Thermistor Error vs Temperature 1.0 1.0 0.8 0.8 0.8 0.6 0.6 0.6 0.4 0.4 0.4 0.2 0.2 0.2 ERROR (°C) 1.0 0 –0.2 ERROR (°C) ERROR (°C) 0.4 –0.6 –0.8 ERROR (°C) RTD NI-120 RTD Error and RMS Noise vs Temperature RTD PT-100 Error and RMS Noise vs Temperature ERROR/RMS NOISE (°C) ERROR/RMS NOISE (°C) RTD PT-200 Error and RMS Noise vs Temperature 0 –0.2 0 –0.2 –0.4 –0.4 –0.4 –0.6 –0.6 –0.6 –0.8 –0.8 –0.8 –1.0 –40 –20 0 20 40 60 80 100 120 140 THERMISTOR TEMPERATURE (°C) –1.0 –40 –20 0 20 40 60 80 100 120 140 THERMISTOR TEMPERATURE (°C) –1.0 –40 –20 0 20 40 60 80 100 120 140 THERMISTOR TEMPERATURE (°C) 2983 G22 2983 G23 2983 G24 2983fc For more information www.linear.com/LTC2983 7 LTC2983 TYPICAL PERFORMANCE CHARACTERISTICS Diode Error and Repeatability vs Temperature Offset vs Temperature 1.0 0.8 1.0 OFFSET (µV) 0.2 0 –0.2 –0.4 NOISE (µVRMS) 1.0 0.4 ERROR (°C) 1.2 1.5 0.6 0.5 0 –0.5 VDD = 5.25V VDD = 4.1V VDD = 2.85V –1.5 –0.8 –1.0 –40 20 80 DIODE TEMPERATURE (°C) –2.0 –50 140 –25 2983 G27 16.0 VDD = 5.25V VDD = 4.1V VDD = 2.85V 50 0 25 50 75 100 LTC2983 TEMPERATURE (°C) 15.6 0 –50 125 –25 0 25 50 75 100 LTC2983 TEMPERATURE (°C) 2.5005 15.2 15.0 14.8 14.6 2.5 2.49975 14.4 10 VREFOUT REFOUT vs Temperature 2.50025 VREFOUT (V) IIDLE (mA) 20 125 2983 G14 15.4 30 VDD = 5.25V VDD = 4.1V VDD = 2.85V 0.2 VDD = 5.25V VDD = 4.1V VDD = 2.85V 15.8 40 ISLEEP (µA) 0.4 One Shot Conversion Current vs Temperature 60 14.2 0 –50 –25 0 25 50 75 100 LTC2983 TEMPERATURE (°C) 0 –50 125 –25 Channel Input Leakage Current vs Temperature Temperature CH2 OFFSET ERROR (µV) 1.0 0.8 0.6 0.4 0 1 2 3 4 INPUT VOLTAGE (V) 5 2983 G18 2983 G28 6 Adjacent Channel Offset Error vs Input Fault Voltage 2.5 2.5 2.0 2.0 1.5 1.0 0.5 –0.5 4.95 1.5 1.0 0.5 0 0 0.2 –1 2.4995 –50 –30 –10 10 30 50 70 90 110 130 TEMPERATURE (°C) Adjacent Channel Offset Error vs Input Fault Voltage (VDD = 5V) 125°C 90°C 25°C –45°C 1.2 125 CH2 OFFSET ERROR (µV) 1.4 0 25 50 75 100 LTC2983 TEMPERATURE (°C) 2983 G16 2983 G15 INPUT LEAKAGE (nA) 0.6 2983 G13 ISLEEP vs Temperature 8 0.8 –1.0 –0.6 0 Noise vs Temperature 2.0 5 5.05 5.1 5.15 5.2 5.25 5.3 5.35 CH1 FAULT VOLTAGE (V) 2983 G25 –0.5 0 –0.05 –0.1 –0.15 –0.2 –0.25 –0.3 –0.35 CH1 FAULT VOLTAGE (V) 2983 G26 2983fc For more information www.linear.com/LTC2983 LTC2983 PIN FUNCTIONS GND (Pins 1, 3, 5, 7, 9, 12, 15, 44): Ground. Connect each of these pins to a common ground plane through a low impedance connection. All eight pins must be grounded for proper operation. VDD (Pins 2, 4, 6, 8, 45): Analog Power Supply. Tie all five pins together and bypass as close as possible to the device, to ground with a 0.1μF capacitor. VREF_BYP( Pin 11): Internal Reference Power. This is an internal supply pin, do not load this pin with external circuitry. Decouple with a 0.1µF capacitor to GND. VREFOUT (Pin 13): Reference Output Voltage. Short to VREFP. A minimum 1μF capacitor to ground is required. Do not load this pin with external circuitry. VREFP (Pin 14): Positive Reference Input. Tie to VREFOUT. CH1 to CH20 (Pin 16 to Pin 35): Analog Inputs. May be programmed for single-ended, differential, or ratiometric operation. The voltage on these pins can have any value between GND – 50mV and VDD – 0.3V. Unused pins can be grounded or left floating. COM (Pin 36): Analog Input. The common negative input for all single-ended configurations. The voltage on this pin can have any value between GND – 50mV and VDD – 0.3V. This pin is typically tied to ground for temperature measurements. INTERRUPT (Pin 37): This pin outputs a LOW when the device is busy either during start-up or while a conversion cycle is in progress. This pin goes HIGH at the conclusion of the start-up state or conversion cycle. SCK (Pin 38): Serial Clock Pin. Data is shifted out of the device on the falling edge of SCK and latched by the device on the rising edge. SDO (Pin 39): Serial Data Out. During the data output state, this pin is used as the serial data output. When the chip select pin is HIGH, the SDO pin is in a high impedance state. SDI (Pin 40): Serial Data Input. Used to program the device. Data is latched on the rising edge of SCK. CS (Pin 41): Active Low Chip Select. A low on this pin enables the digital input/output. A HIGH on this pin places SDO in a high impedance state. A falling edge on CS marks the beginning of a SPI transaction and a rising edge marks the end. RESET (Pin 42): Active Low Reset. While this pin is LOW, the device is forced into the reset state. Once this pin is returned HIGH, the device initiates its start-up sequence. LDO (Pin 43): 2.5V LDO Output. Bypass with a 10µF capacitor to GND. This is an internal supply pin, do not load this pin with external circuitry. Q3, Q2, Q1 (Pins 46, 47, 48): External Bypass Pins for –200mV integrated Charge Pump. Tie a 10µF X7R capacitor between Q1 and Q2 close to each pin. Tie a 10µF X5R capacitor from Q3 to Ground. These are internal supply pins, do not make additional connections. 2983fc For more information www.linear.com/LTC2983 9 LTC2983 BLOCK DIAGRAM VREFP VREF_BYP 1µF 0.1µF VREFOUT VDD Q1 10ppm/°C REFERENCE CHARGE PUMP Q2 10µF Q3 10µF LDO LDO 10µF ADC1 CH1 TO CH20 ROM 21:6 MUX RAM COM ADC2 INTERRUPT SDO PROCESSOR SCK SDI ADC3 CS RESET EXCITATION CURRENT SOURCES GND 2983 BD 10 2983fc For more information www.linear.com/LTC2983 LTC2983 TEST CIRCUITS VDD 1.69k SDO SDO 1.69k CLOAD = 20pF CLOAD = 20pF Hi-Z TO VOH VOL TO VOH VOH TO Hi-Z Hi-Z TO VOL VOH TO VOL VOL TO Hi-Z 2983 TC01 TIMING DIAGRAM SPI Timing Diagram t4 CS SDO t1 t5 t2 t7 SCK SDI 2983 TD01 t3 t6 2983fc For more information www.linear.com/LTC2983 11 LTC2983 OVERVIEW The LTC2983 measures temperature using the most common sensors (thermocouples, RTDs, thermistors, and diodes). It includes all necessary active circuitry, switches, measurement algorithms, and mathematical conversions to determine the temperature for each sensor type. Thermocouples can measure temperatures from as low as –265°C to over 1800°C. Thermocouples generate a voltage as a function of the temperature difference between the tip (thermocouple temperature) and the electrical connection on the circuit board (cold junction temperature). In order to determine the thermocouple temperature, an accurate measurement of the cold junction temperature is required; this is known as cold junction compensation. The cold junction temperature is usually determined by placing a separate (non-thermocouple) temperature sensor at the cold junction. The LTC2983 allows diodes, RTDs, and thermistors to be used as cold junction sensors. In order to convert the voltage output from the thermocouple into a temperature result, a high order polynomial equation (up to 14th order) must be solved. The LTC2983 has these polynomials built in for virtually all standard thermocouples (J, K, N, E, R, S, T, and B). Additionally, inverse polynomials must be solved for the cold junction temperature. The LTC2983 simultaneously measures the thermocouple output and the cold junction temperature and performs all required calculations to report the thermocouple temperature in °C or °F. It directly digitizes both positive and negative voltages (down to 50mV below ground) from a single ground referenced supply, includes sensor burnout detection, and allows external protection/anti-aliasing circuits without the need of buffer circuits. Diodes are convenient low cost sensor elements and are often used to measure cold junction temperatures in thermocouple applications. Diodes are typically used to measure temperatures from –60°C to 130°C, which is 12 suitable for most cold junction applications. Diodes generate an output voltage that is a function of temperature and excitation current. When the difference of two diode output voltages are taken at two different excitation current levels, the result (∆VBE) is proportional to temperature. The LTC2983 accurately generates excitation currents, measures the diode voltages, and calculates the temperature in °C or °F. RTDs and thermistors are resistors that change value as a function of temperature. RTDs can measure temperatures over a wide temperature range, from as low as –200°C to 850°C while thermistors typically operate from –40°C to 150°C. In order to measure one of these devices a precision sense resistor is tied in series with the sensor. An excitation current is applied to the network and a ratiometric measurement is made. The value, in Ω, of the RTD/thermistor can be determined from this ratio. This resistance is used to determine the temperature of the sensor element using a table lookup (RTDs) or solving Steinhart-Hart equations (thermistors). The LTC2983 automatically generates the excitation current, simultaneously measures the sense resistor and thermistor/RTD voltage, calculates the sensor resistance and reports the result in °C. The LTC2983 can digitize most RTD types (PT-10, PT-50, PT-100, PT-200, PT-500, PT-1000, and NI-120), has built in coefficients for many curves (American, European, Japanese, and ITS-90), and accommodates 2-wire, 3-wire, and 4-wire configurations. It also includes coefficients for calculating the temperature of standard 2.252k, 3k, 5k, 10k , and 30k thermistors. It can be configured to share one sense resistor among multiple RTDs/thermistors and to rotate excitation current sources to remove parasitic thermal effects. In addition to built-in linearization coefficients, the LTC2983 provides the means of inserting custom coefficients for both RTDs and thermistors. 2983fc For more information www.linear.com/LTC2983 LTC2983 OVERVIEW Table 1. LTC2983 Error Contribution and Peak Noise Errors SENSOR TYPE TEMPERATURE RANGE ERROR CONTRIBUTION PEAK-TO-PEAK NOISE Type K Thermocouple –200°C to 0°C 0°C to 1372°C ±(Temperature • 0.23% + 0.05)°C ±(Temperature • 0.12% + 0.05)°C ±0.08°C Type J Thermocouple –210°C to 0°C 0°C to 1200°C ±(Temperature • 0.23% + 0.05)°C ±(Temperature • 0.10% + 0.05)°C ±0.07°C Type E Thermocouple –200°C to 0°C 0°C to 1000°C ±(Temperature • 0.18% + 0.05)°C ±(Temperature • 0.10% + 0.05)°C ±0.06°C Type N Thermocouple –200°C to 0°C 0°C to 1300°C ±(Temperature • 0.27% + 0.08)°C ±(Temperature • 0.10% + 0.08)°C ±0.13°C Type R Thermocouple 0°C to 1768°C ±(Temperature • 0.10% + 0.4)°C ±0.62°C Type S Thermocouple 0°C to 1768°C ±(Temperature • 0.10% + 0.4)°C ±0.62°C Type B Thermocouple 400°C to 1820°C ±(Temperature • 0.10%)°C ±0.83°C Type T Thermocouple –250°C to 0°C 0°C to 400°C ±(Temperature • 0.15% + 0.05)°C ±(Temperature • 0.10% + 0.05)°C ±0.09°C External Diode (2 Reading) –40°C to 85°C ±0.25°C ±0.05°C External Diode (3 Reading) –40°C to 85°C ±0.25°C ±0.2°C –200°C to 800°C –200°C to 800°C –200°C to 800°C –200°C to 800°C ±0.1°C ±0.1°C ±0.1°C ±0.1°C ±0.05°C ±0.05°C ±0.02°C ±0.01°C –40°C to 85°C ±0.1°C ±0.01°C Platinum RTD - PT-10, RSENSE = 1kΩ Platinum RTD - PT-100, RSENSE = 2kΩ Platinum RTD - PT-500, RSENSE = 2kΩ Platinum RTD - PT-1000, RSENSE = 2kΩ Thermistor, RSENSE = 10kΩ Table 1 shows the estimated system accuracy and noise associated with specific temperature sensing devices. System accuracy and peak-to-peak noise include the effects of the ADC, internal amplifiers, excitation current sources, and integrated reference for I-grade parts. Accuracy and noise are the worst-case errors calculated from the guaranteed maximum ADC and reference specifications. Peak-to-peak noise values are calculated at 0°C (except type B was calculated at 400°C) and diode measurements use AVG = ON mode. Thermocouple errors do not include the errors associated with the cold junction measurement. Errors associated with a specific cold junction sensor within the operating temperature range can be combined with the errors for a given thermocouple for total temperature measurement accuracy. 2983fc For more information www.linear.com/LTC2983 13 LTC2983 OVERVIEW Memory Map followed by the address and then data. Channel assignment data resides in memory locations 0x200 to 0x24F and can be programmed via the SPI interface as shown in Figure 2. A write is initiated by sending the write instruction byte = 0x02 followed by the address and then data. Conversions are initiated by writing the conversion control byte (see Table 6) into memory location 0x000 (command status register). The LTC2983 channel assignment, configuration, conversion start, and results are all accessible via the RAM (see Table 2A). Table 2B details the valid SPI instruction bytes for accessing memory. The channel conversion results are mapped into memory locations 0x010 to 0x05F and can be read using the SPI interface as shown in Figure 1. A read is initiated by sending the read instruction byte = 0x03 Table 2A. Memory Map LTC2983 MEMORY MAP SEGMENT START ADDRESS END ADDRESS SIZE (BYTES) Command Status Register 0x000 0x000 1 Reserved 0x001 0x00F 15 Temperature Result Memory 20 Words - 80 Bytes 0x010 0x05F 80 Reserved 0x060 0x0EF 144 Global Configuration Register 0x0F0 0x0F0 1 Reserved 0x0F1 0x0F3 3 Measure Multiple Channels Bit Mask 0x0F4 0x0F7 4 Reserved 0x0F8 0x0F8 1 Reserved 0x0F9 0x0FE 6 Mux Configuration Delay 0x0FF 0x0FF 1 Reserved 0x100 0x1FF 256 Channel Assignment Data 0x200 0x24F 80 Custom Sensor Table Data 0x250 0x3CF 384 Reserved 0x3D0 0x3FF 48 DESCRIPTION See Table 6, Initiate Conversion, Sleep Command See Tables 8 to 10, Read Result See Tables 65, 66, Run Multiple Conversions See MUX Configuration Delay Section of Data Sheet See Tables 3, 4, Channel Assignment Table 2B. SPI Instruction Byte INSTRUCTION SPI INSTRUCTION BYTE DESCRIPTION Read 0b00000011 See Figure 1 Write 0b00000010 See Figure 2 No Opp 0bXXXXXX0X 14 2983fc For more information www.linear.com/LTC2983 LTC2983 OVERVIEW CS • • • SCK RECEIVER SAMPLES DATA ON RISING EDGE SDI TRANSMITTER TRANSITIONS DATA ON FALLING EDGE I7 I6 I5 I4 I3 I2 I1 I0 0 0 0 0 0 0 1 1 0 0 0 0 A11 A10 A9 A8 A7 A6 A5 A4 A3 A2 A1 A0 D7 SDO D6 D5 D4 D3 D2 D1 D0 • • • SUBSEQUENT DATA BYTES MAY FOLLOW SPI INSTRUCTION BYTE READ = 0x03 16-BIT ADDRESS FIELD FIRST DATA BYTE USER MEMORY READ TRANSACTION 2983 F01 Figure 1. Memory Read Operation CS • • • SCK RECEIVER SAMPLES DATA ON RISING EDGE SDI TRANSMITTER TRANSITIONS DATA ON FALLING EDGE I7 I6 I5 I4 I3 I2 I1 I0 0 0 0 0 0 0 1 0 SPI INSTRUCTION BYTE WRITE = 0x02 0 0 0 0 A11 A10 A9 A8 A7 A6 A5 A4 A3 A2 A1 A0 D7 D6 D5 D4 D3 D2 D1 D0 • • • SUBSEQUENT DATA BYTES MAY FOLLOW 16-BIT ADDRESS FIELD USER MEMORY WRITE TRANSACTION FIRST DATA BYTE 2983 F02 Figure 2. Memory Write Operation 2983fc For more information www.linear.com/LTC2983 15 LTC2983 APPLICATIONS INFORMATION The LTC2983 combines high accuracy with ease of use. The basic operation is simple and is composed of five states (see Figure 3). POWER-UP, SLEEP OR RESET 5.Read Results. In this state, the user has access to RAM and can read the completed conversion results and fault status bits. It is also possible for the user to modify/append the channel assignment data during the read results state. START-UP ≈ 200ms(MAX) CHANNEL ASSIGNMENT INITIATE CONVERSION Conversion State Details State 1: Start-Up CONVERSION (OPTIONAL) STATUS CHECK COMPLETE? applicable). The user is locked out of RAM access while in the state (except for reading status location 0x000). The end of conversion is indicated by both the INTERRUPT pin going HIGH and a status register START bit going LOW and DONE bit going HIGH. The start-up state automatically occurs when power is applied to the LTC2983. If the power drops below a threshold of ≈2.6V and then returns to the normal operating voltage (2.85V to 5.25V), the LTC2983 resets and enters the powerup state. Note that the LTC2983 also enters the start-up state at the conclusion of the sleep state. The start-up state can also be entered at any time during normal operation by pulsing the RESET pin low. NO YES READ RESULTS 2983 F03 Figure 3. Basic Operation Conversion States Overview 1.Start-Up. After power is applied to the LTC2983 (VDD > 2.6V), there is a 200ms wake up period. During this time, the LDO, charge pump, ADCs, and reference are powered up and the internal RAM is initialized. Once start-up is complete, the INTERRUPT pin goes HIGH and the command status register will return a value of 0x40 (Start bit = 0, Done bit = 1) when read. 2. Channel Assignment. The device automatically enters the channel assignment state after start-up is complete. While in this state, the user writes sensor specific data for each input channel into RAM. The assignment data contains information about the sensor type, pointers to cold junction sensors or sense resistors, and sensor specific parameters. In the first phase of the start-up state all critical analog circuits are powered up. This includes the LDO, reference, charge pump and ADCs. During this first phase, the command status register will be inaccessible to the user. This phase takes a maximum of 100mS to complete. Once this phase completes, the command status register will be accessible and return a value of 0x80 until the LTC2983 is completely initialized. Once the LTC2983 is initialized and ready to use, the interrupt pin will go high and the command status register will return a read value of 0x40 (Start bit = 0, Done bit = 1). At this point the LTC2983 is fully initialized and is ready to perform a conversion. State 2: Channel Assignment 3. Initiate Conversion. A conversion is initiated by writing a measurement command into RAM memory location 0x000. This command is a pointer to the channel in which the conversion will be performed. The LTC2983 RAM can be programmed with up to 20 sets of 32-bit (4-byte) channel assignment data. These reside sequentially in RAM with a one-to-one correspondence to each of the 20 analog input channels (see Table 3). Channels that are not used should have their channel assignment data set to all zeros (default at START-UP). 4.Conversion. A new conversion begins automatically following an Initiate Conversion command. In this state, the ADC is running a conversion on the specified channel and associated cold junction or RSENSE channel (if The channel assignment data contains all the necessary information associated with the specific sensor tied to that channel (see Table 4). The first five bits determine the sensor type (see Table 5). Associated with each sensor are sensor 16 For more information www.linear.com/LTC2983 2983fc LTC2983 APPLICATIONS INFORMATION Table 3. Channel Assignment Memory Map CHANNEL ASSIGNMENT NUMBER CONFIGURATION DATA START ADDRESS CONFIGURATION DATA ADDRESS + 1 CONFIGURATION DATA ADDRESS + 2 CONFIGURATION DATA END ADDRESS + 3 SIZE (BYTES) CH1 0x200 0x201 0x202 0x203 4 CH2 0x204 0x205 0x206 0x207 4 CH3 0x208 0x209 0x20A 0x20B 4 CH4 0x20C 0x20D 0x20E 0x20F 4 CH5 0x210 0x211 0x212 0x213 4 CH6 0x214 0x215 0x216 0x217 4 CH7 0x218 0x219 0x21A 0x21B 4 CH8 0x21C 0x21D 0x21E 0x21F 4 CH9 0x220 0x221 0x222 0x223 4 CH10 0x224 0x225 0x226 0x227 4 CH11 0x228 0x229 0x22A 0x22B 4 CH12 0x22C 0x22D 0x22E 0x22F 4 CH13 0x230 0x231 0x232 0x233 4 CH14 0x234 0x235 0x236 0x237 4 CH15 0x238 0x239 0x23A 0x23B 4 CH16 0x23C 0x23D 0x23E 0x23F 4 CH17 0x240 0x241 0x242 0x243 4 CH18 0x244 0x245 0x246 0x247 4 CH19 0x248 0x249 0x24A 0x24B 4 CH20 0x24C 0x24D 0x24E 0x24F 4 Table 4. Channel Assignment Data SENSOR TYPE Channel Assignment Memory Location 31 30 29 28 27 Unassigned (Default) Type = 0 Thermocouple Type = 1 to 9 RTD Thermistor SENSOR SPECIFIC CONFIGURATION Configuration Data Start Address 26 25 Configuration Data Start Address + 1 24 23 22 21 20 19 Configuration Data Start Address + 2 18 Configuration Data Start Address + 3 17 16 15 14 13 12 11 10 9 8 7 6 5 4 3 2 1 0 Channel Disabled Cold Junction Channel Assignment [4:0] Type = 10 to 18 RSENSE Channel Assignment [4:0] SGL=1 OC DIFF=0 Check OC Current [1:0] 2, 3, 4 Wire Excitation Mode Type = 19 to 27 RSENSE Channel Assignment SGL=1 [4:0] DIFF=0 Excitation Mode 0 0 0 0 0 0 Custom Address [5:0] Custom Length - 1 [5:0] Excitation Curve Current [3:0] [1:0] Custom Address [5:0] Custom Length - 1 [5:0] Custom Address [5:0] Custom Length - 1 [5:0] Excitation Current 0 0 [3:0] 0 Diode Type = 28 SGL=1 2 to 3 Avg Current Ideality Factor (2, 20) Value from 0 to 4 with 1/1048576 Resolution DIFF=0 Reading on [1:0] All Zeros Use Factory Set Default in ROM Sense Resistor Type = 29 Sense Resistor Value (17, 10) Up to 131,072Ω with 1/1024Ω Resolution Direct ADC Type = 30 SGL=1 DIFF=0 Reserved Type = 31 Not Used Not Used 2983fc For more information www.linear.com/LTC2983 17 LTC2983 APPLICATIONS INFORMATION Table 5. Sensor Type Selection 31 30 29 28 27 SENSOR TYPE 0 0 0 0 0 Unassigned 0 0 0 0 1 Type J Thermocouple 0 0 0 1 0 Type K Thermocouple 0 0 0 1 1 Type E Thermocouple 0 0 1 0 0 Type N Thermocouple 0 0 1 0 1 Type R Thermocouple 0 0 1 1 0 Type S Thermocouple 0 0 1 1 1 Type T Thermocouple 0 1 0 0 0 Type B Thermocouple 0 1 0 0 1 Custom Thermocouple 0 1 0 1 0 RTD PT-10 0 1 0 1 1 RTD PT-50 0 1 1 0 0 RTD PT-100 0 1 1 0 1 RTD PT-200 0 1 1 1 0 RTD PT-500 0 1 1 1 1 RTD PT-1000 1 0 0 0 0 RTD 1000 (0.00375) 1 0 0 0 1 RTD NI-120 1 0 0 1 0 RTD Custom 1 0 0 1 1 software includes a utility for checking configuration data and generating annotated C-code for programming the channel assignment data. State 3: Initiate Conversion Once the channel assignment is complete, the device is ready to begin a conversion. A conversion is initiated by writing Start (B7 = 1) and Done (B6 = 0) followed by the desired input channel (B4 – B0) into RAM memory location 0x000 (see Tables 6 and 7). It is possible to initiate a measurement cycle on multiple channels by setting the channel selection bits (B4 to B0) to 00000; see the Running Conversions Consecutively on Multiple Channels section of the data sheet. Table 6. Command Status Register B7 B6 Start = 1 Done = 0 1 0 B5 B4 B3 B2 B1 B0 0 Channel Selection 1 to 20 Start Conversion 0 1 Initiate Sleep 0 1 1 1 Table 7. Input Channel Mapping B7 B6 B5 B4 B3 B2 B1 Thermistor 44004/44033 2.252kΩ at 25°C 1 1 0 0 0 0 1 0 1 0 1 1 B0 CHANNEL SELECTED 0 0 0 0 0 Multiple Channels 0 0 0 0 1 CH1 0 0 0 0 1 0 CH2 0 0 0 0 1 1 CH3 0 0 0 0 1 0 0 CH4 0 0 0 0 1 0 1 CH5 1 0 0 0 0 1 1 0 CH6 1 0 0 0 0 1 1 1 CH7 1 0 0 0 1 0 0 0 CH8 1 0 0 0 1 0 0 1 CH9 1 0 0 0 1 0 1 0 CH10 1 0 0 0 1 0 1 1 CH11 1 0 1 0 0 Thermistor 44005/44030 3kΩ at 25°C 1 0 1 0 1 Thermistor 44007/44034 5kΩ at 25°C 1 0 1 1 0 Thermistor 44006/44031 10kΩ at 25°C 1 0 1 1 1 Thermistor 44008/44032 30kΩ at 25°C 1 1 0 0 0 Thermistor YSI 400 2.252kΩ at 25°C 1 1 0 0 1 Thermistor Spectrum 1003k 1kΩ 1 1 0 1 0 Thermistor Custom Steinhart-Hart 1 1 0 1 1 Thermistor Custom Table 1 1 1 0 0 Diode 1 1 1 0 1 Sense Resistor 1 1 1 1 0 Direct ADC 1 0 0 0 1 1 0 0 CH12 1 1 1 1 1 Reserved 1 0 0 0 1 1 0 1 CH13 1 0 0 0 1 1 1 0 CH14 1 0 0 0 1 1 1 1 CH15 1 0 0 1 0 0 0 0 CH16 1 0 0 1 0 0 0 1 CH17 1 0 0 1 0 0 1 0 CH18 1 0 0 1 0 0 1 1 CH19 1 0 0 1 0 1 0 0 CH20 1 0 0 1 0 1 1 1 Sleep specific configurations. These include pointers to cold junction or sense resistor channels, pointers to memory locations of custom linearization data, sense resistor values and diode ideality factors. Also included in this data are, if applicable, the excitation current level, single-ended/differential input mode, as well as sensor specific controls. Separate detailed operation sections for thermocouples, RTDs, diodes, thermistors, and sense resistors describe the assignment data associated with each sensor type in more detail. The LTC2983 demonstration 18 All Other Combinations Reserved 2983fc For more information www.linear.com/LTC2983 LTC2983 APPLICATIONS INFORMATION Bits B4 to B0 determine which input channel the conversion is performed upon and are simply the binary equivalent of the channel number (see Table 7). Bit B5 should be set to 0. Bits B7 and B6 serve as start/done bits. In order to start a conversion, these bits must be set to “10” (B7=1 and B6=0). When the conversion begins, the INTERRUPT pin goes LOW. Once the conversion is complete, bits B7 and B6 will toggle to “01” (B7=0 and B6=1) (Address = 0x000) and the INTERRUPT pin will go HIGH, indicating the conversion is complete and the result is available. State 4: Conversion The measurement cycle starts after the initiate conversion command is written into RAM location 0x000 (Table 6). The LTC2983 simultaneously measures the selected input sensor, sense resistors (RTDs and thermistors), and cold junction temperatures if applicable (thermocouples). Once the conversion is started, the user is locked out of the RAM, with the exception of reading status data stored in RAM memory location 0x000. Once the conversion is started the INTERRUPT pin goes low. Depending on the sensor configuration, two or three 82ms cycles are required per temperature result. These correspond to conversion rates of 167ms and 251ms, respectively. Details describing these modes are described in the 2- and 3-cycle Conversion Modes section of the data sheet. The end of conversion can be monitored either through the interrupt pin (LOW to HIGH transition), or by reading the command status register in RAM memory location 0x000 (start bit, B7, toggles from 1 to 0 and DONE bit, B6, toggles from 0 to 1). State 5: Read Results Once the conversion is complete, the conversion results can be read from RAM memory locations corresponding to the input channel (see Table 8). The conversion result is 32 bits long and contains both the sensor temperature (D23 to D0) and sensor fault data (D31 to D24) (see Tables 9A and 9B). Table 8. Conversion Result Memory Map CONVERSION CHANNEL START ADDRESS END ADDRESS SIZE (BYTES) CH1 0x010 0x013 4 CH2 0x014 0x017 4 CH3 0x018 0x01B 4 CH4 0x01C 0x01F 4 CH5 0x020 0x023 4 CH6 0x024 0x027 4 CH7 0x028 0x02B 4 CH8 0x02C 0x02F 4 CH9 0x030 0x033 4 CH10 0x034 0x037 4 CH11 0x038 0x03B 4 CH12 0x03C 0x03F 4 CH13 0x040 0x043 4 CH14 0x044 0x047 4 CH15 0x048 0x04B 4 CH16 0x04C 0x04F 4 CH17 0x050 0x053 4 CH18 0x054 0x057 4 CH19 0x058 0x05B 4 CH20 0x05C 0x05F 4 The result is reported in °C for all temperature sensors with a range of –273.16°C to 8192°C and 1/1024°C resolution or in °F with a range of –459.67°F to 8192°F with 1/1024°F resolution. Included with the conversion result are seven sensor fault bits and a valid bit. These bits are set to a 1 if there was a problem associated with the corresponding conversion result (see Table 10). Two types of errors are reported: hard errors and soft errors. Hard errors indicate the reading is invalid and the resulting temperature reported is –999°C or °F. Soft errors indicate operation beyond the normal temperature range of the sensor or the input range of the ADC. In this case, the calculated temperature is reported but the accuracy may be compromised. Details relating to each fault type are sensor specific and are described in detail in the sensor specific sections of this data sheet. Bit D24 is the valid bit and will be set to a 1 for valid data. Once the data read is complete, the device is ready for a new initiate conversion command. In cases where new channel configuration data is required, the user has access to the RAM in order to modify existing channel assignment data. 2983fc For more information www.linear.com/LTC2983 19 LTC2983 APPLICATIONS INFORMATION Table 9A. Example Data Output Words (°C) START ADDRESS D31 D30 D29 D28 D27 D26 START ADDRESS + 1 D25 D24 START ADDRESS + 2 START ADDRESS + 3 (END ADDRESS) D23 D22 D21 D20 D19 D18 D17 D16 D15 D14 D13 D12 D11 D10 D9 D8 D7 D6 D5 D4 D3 D2 D1 D0 Fault Data SIGN MSB Temperature Sensor ADC CJ CJ Sensor Sensor ADC Valid Hard Hard Hard Soft Over Under Out If 1 Fault Fault Fault Fault Range Range of Fault Fault Range Fault 8191.999°C LSB 1°C 4096°C 1 0 1 1 1 1 1 1 1 1 1 1 1 1 1/1024°C 1 1 1 1 1 1 1 1 1 1 1 1024°C 1 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1°C 1 0 0 0 0 0 0 0 0 0 0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 1/1024°C 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 0°C 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 –1/1024°C 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 –1°C 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 0 0 0 0 0 0 0 0 0 0 –273.15°C 1 1 1 1 1 1 0 1 1 1 0 1 1 1 0 1 1 0 1 1 0 0 1 1 1 Table 9B. Example Data Output Words (°F) START ADDRESS D31 D30 D29 D28 D27 D26 START ADDRESS + 1 D25 START ADDRESS + 2 START ADDRESS + 3 (END ADDRESS) D24 D23 D22 D21 D20 D19 D18 D17 D16 D15 D14 D13 D12 D11 D10 D9 D8 D7 D6 D5 D4 D3 D2 D1 D0 Fault Data SIGN MSB Temperature Sensor ADC CJ CJ Sensor Sensor ADC Valid Hard Hard Hard Soft Over Under Out If 1 Fault Fault Fault Fault Range Range of Fault Fault Range Fault LSB 1°F 4096°F 1/1024°F 8191.999°F 1 0 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1024°F 1 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1°F 1 0 0 0 0 0 0 0 0 0 0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 1/1024°F 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 0°F 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 –1/1024°F 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 –1°F 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 0 0 0 0 0 0 0 0 0 0 –459.67°F 1 1 1 1 1 1 0 0 0 1 1 0 1 0 0 0 1 0 1 0 1 0 0 1 0 Table 10. Sensor Fault Reporting BIT FAULT ERROR TYPE DESCRIPTION OUTPUT RESULT D31 Sensor Hard Fault Hard Bad Sensor Reading –999°C or °F D30 Hard ADC-Out-of-Range Hard Bad ADC Reading (Could Be Large External Noise Event) –999°C or °F D29 CJ Hard Fault Hard Cold Junction Sensor Has a Hard Fault Error –999°C or °F D28 CJ Soft Fault Soft Cold Junction Sensor Result Is Beyond Normal Range Suspect Reading D27 Sensor Over Range Soft Sensor Reading Is Above Normal Range Suspect Reading D26 Sensor Under Range Soft Sensor Reading Is Below Normal Range Suspect Reading D25 ADC Out-of-Range Soft ADC Absolute Input Voltage Is Beyond ±1.125 • VREF/2 Suspect Reading D24 Valid NA Result Valid (Should Be 1) Discard Results if 0 Suspect Reading 20 2983fc For more information www.linear.com/LTC2983 LTC2983 APPLICATIONS INFORMATION THERMOCOUPLE MEASUREMENTS Table 11. Thermocouple Channel Assignment Word (1) THERMOCOUPLE (2) COLD JUNCTION TYPE CHANNEL POINTER TABLES 4, 12 Measurement Type Types 1 to 9 (4) CUSTOM THERMOCOUPLE DATA POINTER TABLE 14 TABLES 67 TO 69 TABLE 13 31 30 29 28 27 26 25 24 23 22 Thermocouple (3) SENSOR CONFIGURATION 21 20 19 18 17 16 15 14 13 12 11 10 9 8 7 6 5 4 3 2 1 0 Cold Junction SGL=1 OC OC 0 0 0 0 0 Channel Assignment DIFF=0 Check Current [4:0] [1:0] Channel Assignment – Thermocouples For each thermocouple tied to the LTC2983, a 32-bit channel assignment word is programmed into a memory location corresponding to the channel the sensor is tied to (see Table 11). This word includes (1) thermocouple type, (2) cold junction channel pointer, (3) sensor configuration, and (4) custom thermocouple data pointer. 0 Custom Address [5:0] Custom Length –1 [5:0] sensor is assigned to (see Table 13). When a conversion is performed on a channel tied to a thermocouple, the cold junction sensor is simultaneously and automatically measured. The final output data uses the embedded coefficients stored in ROM to automatically compensate the cold junction temperature and output the thermocouple sensor temperature. Table 13. Cold Junction Channel Pointer (1) Thermocouple Type The thermocouple type is determined by the first five input bits B31 to B27 as shown in Table 12. Standard NIST coefficients for types J,K,E,N,R,S,T and B thermocouples are stored in the device ROM. If custom thermocouples are used, the custom thermocouple sensor type can be selected. In this case, user-specific data can be stored in the on-chip RAM starting at the address defined in the custom thermocouple data pointer. (2) Cold Junction Channel Pointer The cold junction compensation can be a diode, RTD, or thermistor. The cold junction channel pointer tells the LTC2983 which channel (1 to 20) the cold junction Table 12. Thermocouple Type (1) THERMOCOUPLE TYPE B31 B30 B29 B28 B27 THERMOCOUPLE TYPES 0 0 0 0 1 Type J Thermocouple 0 0 0 1 0 Type K Thermocouple 0 0 0 1 1 Type E Thermocouple 0 0 1 0 0 Type N Thermocouple 0 0 1 0 1 Type R Thermocouple 0 0 1 1 0 Type S Thermocouple 0 0 1 1 1 Type T Thermocouple 0 1 0 0 0 Type B Thermocouple 0 1 0 0 1 Custom Thermocouple (2) COLD JUNCTION CHANNEL POINTER B26 B25 B24 B23 B22 COLD JUNCTION CHANNEL 0 0 0 0 0 No Cold Junction Compensation, 0°C Used for Calculations 0 0 0 0 1 CH1 0 0 0 1 0 CH2 0 0 0 1 1 CH3 0 0 1 0 0 CH4 0 0 1 0 1 CH5 0 0 1 1 0 CH6 0 0 1 1 1 CH7 0 1 0 0 0 CH8 0 1 0 0 1 CH9 0 1 0 1 0 CH10 0 1 0 1 1 CH11 0 1 1 0 0 CH12 0 1 1 0 1 CH13 0 1 1 1 0 CH14 0 1 1 1 1 CH15 1 0 0 0 0 CH16 1 0 0 0 1 CH17 1 0 0 1 0 CH18 1 0 0 1 1 CH19 0 1 0 0 CH20 1 All Other Combinations Invalid 2983fc For more information www.linear.com/LTC2983 21 LTC2983 APPLICATIONS INFORMATION (3) Sensor Configuration The sensor configuration field (see Table 14) is used to select single-ended (B21=1) or differential (B21=0) input and allows selection of open circuit current if internal open-circuit detect is enabled (bit B20). Single-ended readings are measured relative to the COM pin and differential are measured between the selected CHTC and adjacent CHTC-1 (see Figure 4). If open-circuit detection is enabled, B20=1, then the user can select the pulsed current value applied during opencircuit detect using bits B18 and B19 . The user determines the value of the open circuit current based on the size of the external protection resistor and filter capacitor (typically 10µA). This network needs to settle within 50ms to 1µV or less. The duration of the current pulse is approximately 8ms and occurs 50ms before the normal conversion cycle. Thermocouple channel assignments follow the general convention shown in Figure 4. The thermocouple positive terminal ties to CHTC (where TC is the selected channel number) for both the single-ended and differential modes of operation. For single-ended measurements the thermocouple negative terminal and the COM pin are grounded. The thermocouple negative terminal is tied to CHTC-1 for differential measurements. This node can either be grounded or tied to a bias voltage. (4) Custom Thermocouple Data Pointer See Custom Thermocouples section near the end of this data sheet for more information. 22 CHANNEL = CH (1≤ TC ≤ 20) TC ASSIGNMENT CHTC + 0.1µF SINGLE-ENDED – COM CHANNEL = CH (2≤ TC ≤ 20) TC ASSIGNMENT CHTC + 0.1µF DIFFERENTIAL CHTC-1 – 2983 F04 Figure 4. Thermocouple Channel Assignment Convention Table 14. Sensor Configuration (3) SENSOR CONFIGURATION SGL OC CHECK OC CURRENT B21 B20 B19 B18 SINGLE-ENDED/ DIFFERENTIAL OPEN-CIRCUIT CURRENT 0 0 X X Differential External 0 1 0 0 Differential 10µA 0 1 0 1 Differential 100µA 0 1 1 0 Differential 500µA 0 1 1 1 Differential 1mA 1 0 X X Single-Ended External 1 1 0 0 Single-Ended 10µA 1 1 0 1 Single-Ended 100µA 1 1 1 0 Single-Ended 500µA 1 1 1 1 Single-Ended 1mA 2983fc For more information www.linear.com/LTC2983 LTC2983 APPLICATIONS INFORMATION Fault Reporting – Thermocouple Each sensor type has a unique fault reporting mechanism indicated in the upper byte of the data output word. Table 15 shows faults reported in the measurement of thermocouples. Bit D31 indicates the thermocouple sensor is open (broken or not plugged in), the cold junction sensor has a hard fault, or the ADC is out of range. This is indicated by a reading well beyond the normal operating range. Bit D30 indicates a bad ADC reading. This can be a result of either a broken (open) sensor or an excessive noise event (ESD or static discharge into the sensor path). Either of these are a hard error and –999°C or °F is reported. In the case of an excessive noise event, the device should recover and the following conversions will be valid if the noise event was a random, infrequent event. Bit D29 indicates a hard fault occurred at the cold junction sensor and –999°C or °F is reported. Refer to the specific sensor (diode, themistor, or RTD) used for cold junction compensation. Bit D28 indicates a soft fault occurred at the cold junction sensor. A valid temperature is reported, but the accuracy may be compromised since the cold junction sensor is operating outside its normal temperature range. Bits D27 and D26 indicate over or under temperature limits have been exceeded for specific thermocouple types, as defined in Table 16. Bit D25 indicates the absolute voltage measured by the ADC is beyond its normal operating range. This fault reflects a reading that is well beyond the normal range of a thermocouple. Table 16. Thermocouple Temperature Limits THERMOCOUPLE TYPE LOW TEMP LIMIT °C HIGH TEMP LIMIT °C J-Type –210 1200 K-Type –265 1372 E-Type –265 1000 N-Type –265 1300 R-type –50 1768 S-Type –50 1768 T-Type –265 400 B-Type 40 1820 Custom Lowest Table Entry Highest Table Entry Table 15. Thermocouple Fault Reporting BIT FAULT ERROR TYPE DESCRIPTION OUTPUT RESULT D31 Sensor Hard Fault Hard Open Circuit or Hard ADC or Hard CJ –999°C or °F D30 Hard ADC-Out-of-Range Hard Bad ADC Reading (Could Be Large External Noise Event) –999°C or °F D29 CJ Hard Fault Hard Cold Junction Sensor Has a Hard Fault Error –999°C or °F D28 CJ Soft Fault Soft Cold Junction Sensor Result Is Beyond Normal Range Suspect Reading D27 Sensor Over Range Soft Thermocouple Reading Greater Than High Limit Suspect Reading D26 Sensor Under Range Soft Thermocouple Reading Less Than Low Limit Suspect Reading D25 ADC Out-of-Range Soft ADC Absolute Input Voltage Is Beyond ±1.125 • VREF/2 Suspect Reading D24 Valid NA Result Valid (Should Be 1) Discard Results if 0 Valid Reading 2983fc For more information www.linear.com/LTC2983 23 LTC2983 APPLICATIONS INFORMATION DIODE MEASUREMENTS Table 17. Diode Channel Assignment Word (1) SENSOR TYPE (2) SENSOR CONFIGURATION (3) EXCITATION CURRENT TABLE 18 TABLE 19 Measurement Class 31 30 29 28 27 Diode Type = 28 (4) DIODE IDEALITY FACTOR VALUE 26 25 24 23 SGL=1 2 or 3 Avg DIFF=0 Readings on 22 Current [1:0] Channel Assignment – Diode For each diode tied to the LTC2983, a 32-bit channel assignment word is programmed into a memory location corresponding to the channel the sensor is tied to (see Table 17). This word includes (1) diode sensor selection, (2) sensor configuration, (3) excitation current, and (4) diode ideality factor. TABLE 20 21 20 19 18 17 16 15 14 13 12 11 10 9 8 7 6 5 4 3 2 1 0 Non-Ideality Factor (2, 20) Value from 0 to 4 with 1/1048576 Resolution All Zeros Uses a Factory Set Default of 1.003 Bit B24 enables a running average of the diode temperature reading. This reduces the noise when the diode is used as a cold junction temperature element on an isothermal block where temperatures change slowly. The algorithm used for diode averaging is a simple recursive running average. The new value is equal to the average of the current reading plus the previous value. 1) Sensor Type The diode is selected by the first five input bits B31 to B27 (see Table 18). Table 18. Diode Sensor Selection (1) SENSOR TYPE B31 B30 B29 B28 B27 SENSOR TYPE 1 1 1 0 0 Diode NEW VALUE = CURRENT READING PREVIOUS VALUE + 2 2 If the current reading is 2°C above or below the previous value, the new value is reset to the current reading. (3) Excitation Current (2) Sensor Configuration The sensor configuration field (bits B26 to B24) is used to define various diode measurement properties. Configuration bit B26 is set high for single-ended (measurement relative to COM) and low for differential. Bit B25 sets the measurement algorithm. If B25 is low, two conversion cycles (one at 1I and one at 8I current excitation) are used to measure the diode. This is used in applications where parasitic resistance between the LTC2983 and the diode is small. Parasitic resistance effects can be removed by setting bit B25 high, enabling three conversion cycles (one at 1I, one at 4I and one at 8I). The next field in the channel assignment word (B23 to B22) controls the magnitude of the excitation current applied to the diode (see Table 19). In the two conversion cycle mode, the device performs the first conversion at a current equal to 8x the excitation current 1I. The second conversion occurs at 1I. Alternatively, in the three conversion cycle mode the first conversion excitation current is 8I, the second is 4I and the 3rd is 1I. Table 19. Diode Excitation Current Selection (3) EXCITATION CURRENT Table 20. Programming Diode Ideality Factor B23 B22 1I 4I 8I 0 0 10µA 40µA 80µA 0 1 20µA 80µA 160µA 1 0 40µA 160µA 320µA 1 1 80µA 320µA 640µA (4) DIODE IDEALITY FACTOR VALUE B21 B20 B19 B18 B17 B16 B15 B14 B13 B12 B11 B10 B9 B8 B7 B6 B5 B4 B3 B2 B1 B0 Example h 21 20 1.25 0 1 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1.003 (Default) 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1.006 0 1 0 0 0 0 0 0 0 1 1 0 0 0 1 0 0 1 0 0 1 24 2–1 2–2 2–3 2–4 2–5 2–6 2–7 2–8 2–9 2–10 2–11 2–12 2–13 2–14 2–15 2–16 2–17 2–18 2–19 2–20 1 2983fc For more information www.linear.com/LTC2983 LTC2983 APPLICATIONS INFORMATION (4) Diode Ideality Factor The last field in the channel assignment word (B21 to B0) sets the diode ideality factor within the range 0 to 4 with 1/1048576 (2–20) resolution. The top two bits (B21 to B20) are the integer part and bits B19 to B0 are the fractional part of the ideality factor (see Table 20). Diode channel assignments follow the general convention shown in Figure 5. The anode ties to CHD (where D is the selected channel number) for both the single-ended and differential modes of operation, and the cathode is grounded. For differential diode measurements, the cathode is also tied to CHD-1. hard error and –999°C or °F is reported. In the case of an excessive noise event, the device should recover and the following conversions will be valid if the noise event was a random, infrequent event. Bits D29 and D28 are not used for diodes. Bits D27 and D26 indicate over or under temperature limits (defined as T > 130°C or T < –60°C). The calculated temperature is reported, but the accuracy may be compromised. Bit D25 indicates the absolute voltage measured by the ADC is beyond its normal operating range. If a diode is used as the cold junction element, any hard or soft error is flagged in the corresponding thermocouple result (bits D28 and D29 in Table 15). Fault Reporting - Diode CHD Each sensor type has unique fault reporting mechanism indicated in the upper byte of the data output word. Table 21 shows faults reported in the measurement of diodes. Bit D31 indicates the diode is open, shorted, not plugged in, wired backwards, or the ADC reading is bad. Any of these are hard faults and –999°C or °F is reported. Bit D30 indicates a bad ADC reading. This can be a result of either a broken (open) sensor or an excessive noise event (ESD or static discharge into the sensor path). This is a SINGLE-ENDED COM CHD DIFFERENTIAL CHANNEL = CH (1≤ D ≤ 20) D ASSIGNMENT CHANNEL = CH (2≤ D ≤ 20) D ASSIGNMENT CHD-1 2983 F05 Figure 5. Diode Channel Assignment Convention Table 21. Diode Fault Reporting BIT FAULT ERROR TYPE DESCRIPTION OUTPUT RESULT D31 Sensor Hard Fault Hard Open, Short, Reversed, or Hard ADC –999°C or °F D30 Hard ADC-Out-of-Range Hard Bad ADC Reading (Could Be Large External Noise Event) –999°C or °F D29 Not Used for Diodes N/A Always 0 D28 Not Used for Diodes N/A Always 0 D27 Sensor Over Range Soft T > 130°C Suspect Reading D26 Sensor Under Range Soft T < –60°C Suspect Reading D25 ADC Out-of-Range Soft ADC Absolute Input Voltage Is Beyond ±1.125 • VREF/2 Suspect Reading D24 Valid NA Result Valid (Should Be 1) Discard Results if 0 Valid Reading 2983fc For more information www.linear.com/LTC2983 25 LTC2983 APPLICATIONS INFORMATION Example: Single-Ended Type K and Differential Type T Thermocouples with Shared Diode Cold Junction Compensation Figure 6 shows a typical temperature measurement system where two thermocouples share a single cold junction diode. In this example, a Type K thermocouple is tied to CH1 and a Type T thermocouple is tied to CH3 and CH4. They both share a single cold junction diode with ideality factor of η=1.003 tied to CH2. Channel assignment data for both thermocouples and the diode are CH1 TYPE K THERMOCOUPLE ASSIGNED TO CH1 (CHTC=1) CHANNEL ASSIGNMENT MEMORY LOCATIONS 0x200 TO 0x203 RESULT MEMORY LOCATIONS 0x010 TO 0x013 CH2 DIODE COLD JUNCTION ASSIGNED TO CH2 (CHD=2) CHANNEL ASSIGNMENT MEMORY LOCATIONS 0x204 TO 0x207 RESULT MEMORY LOCATIONS 0x014 TO 0x017 0.1µF TYPE K shown in Tables 22 to 24. Thermocouple #1 (Type K) sensor type and configuration data are assigned to CH1. 32-bits of binary configuration data are mapped directly into memory locations 0x200 to 0x203 (see Table 22). The cold junction diode sensor type and configuration data are assigned to CH2. 32-bits of binary configuration data are mapped directly into memory locations 0x204 to 0x207 (see Table 23). Thermocouple #2 (Type T) sensor type and configuration data are assigned to CH4. 32-bits of binary configuration data are mapped directly η = 1.003 CH3 TYPE T CH4 0.1µF TYPE T THERMOCOUPLE JUNCTION ASSIGNED TO CH4 (CHTC=4) CHANNEL ASSIGNMENT MEMORY LOCATIONS 0x20C TO 0x20F RESULT MEMORY LOCATIONS 0x01C TO 0x01F COM 2983 F06 Figure 6. Dual Thermocouple with Diode Cold Junction Example 26 2983fc For more information www.linear.com/LTC2983 LTC2983 APPLICATIONS INFORMATION into memory locations 0x20C to 0x20F (see Table 24). A conversion is initiated on CH1 by writing 10000001 into memory location 0x000. Both the Type K thermocouple and the diode are measured simultaneously. The LTC2983 calculates the cold junction compensation and determines the temperature of the Type K thermocouple. Once the conversion is complete, the INTERRUPT pin goes HIGH and memory location 0x000 becomes 01000001. Similarly, a conversion can be initiated on CH4 by writing 10000100 into memory location 0x000. The results (in °C) can be read from memory locations 0x010 to 0x013 for CH1 and 0x01C to 0x01F for CH4. Table 22. Thermocouple #1 Channel Assignment (Type K, Cold Junction CH2, Single-Ended, 10µA Open-Circuit Detect) CONFIGURATION FIELD DESCRIPTION (1) Thermocouple Type Type K 5 00010 0 0 0 1 0 (2) Cold Junction Channel Pointer CH2 5 00010 (3) Sensor Configuration Single-Ended, 10µA Open-Circuit 4 1100 Not Used Set These Bits to 0 6 000000 Not Custom 12 000000000000 (4) Custom Thermocouple Data Pointer # BITS BINARY DATA MEMORY ADDRESS 0x200 MEMORY ADDRESS 0x201 MEMORY ADDRESS 0x202 MEMORY ADDRESS 0x203 0 0 0 1 0 1 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 Table 23. Diode Channel Assignment (Single-Ended 3-Reading, Averaging On, 20µA/80µA Excitation, Ideality Factor = 1.003)) CONFIGURATION DESCRIPTION # BITS FIELD (1) Sensor Type BINARY DATA Diode 5 (2) Sensor Configuration Single-Ended, 3-Reading, Average On 3 111 (3) Excitation Current 20µA, 80µA, 160µA 2 01 1.003 22 0100000000110001001001 (4) Ideality Factor MEMORY ADDRESS 0x204 MEMORY ADDRESS 0x205 MEMORY ADDRESS 0x206 MEMORY ADDRESS 0x207 11100 1 1 1 0 0 1 1 1 0 1 0 1 0 0 0 0 0 0 0 0 1 1 0 0 0 1 0 0 1 0 0 1 Table 24. Thermocouple #2 Channel Assignment (Type T, Cold Junction CH2, Differential, 100µA Open-Circuit Detect) CONFIGURATION FIELD DESCRIPTION # BITS (1) Thermocouple Type Type T 5 00111 0 0 1 1 1 (2) Cold Junction Channel Pointer CH2 5 00010 (3) Sensor Configuration Differential, 100µA OpenCircuit Current 4 0101 Not Used Set These Bits to 0 6 000000 Not Custom 12 000000000000 (4) Custom Thermocouple Data Pointer BINARY DATA MEMORY ADDRESS 0x20C MEMORY ADDRESS 0x20D MEMORY ADDRESS 0x20E MEMORY ADDRESS 0x20F 0 0 0 1 0 0 1 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 2983fc For more information www.linear.com/LTC2983 27 LTC2983 APPLICATIONS INFORMATION RTD MEASUREMENTS Table 25. RTD Channel Assignment Word (1) RTD TYPE (2) SENSE RESISTOR CHANNEL POINTER (3) SENSOR CONFIGURATION TABLE 26 TABLE 27 TABLE 28 Measurement Class 31 30 29 28 27 26 25 24 23 22 21 20 RTD Type = 10 to 18 RSENSE Channel Assignment [4:0] 2, 3, 4 Wire 19 (4) EXCITATION (5) RTD CURRENT CURVE TABLE 29 18 Excitation Mode TABLE 30 17 16 15 14 13 Excitation Current [3:0] (6) CUSTOM RTD DATA POINTER TABLES 72 TO 74 12 11 10 9 8 7 6 5 4 3 2 1 0 Curve [1:0] Custom Address Custom Length – 1 [5:0] [5:0] Channel Assignment – RTD (2) Sense Resistor Channel Pointer For each RTD tied to the LTC2983, a 32-bit channel assignment word is programmed into a memory location corresponding to the channel the sensor is tied to (see Table 25). This word includes (1) RTD type, (2) sense resistor channel pointer, (3) sensor configuration, (4) excitation current, (5) RTD curve, and (6) custom RTD data pointer. RTD measurements are performed ratiometrically relative to a known RSENSE resistor. The sense resistor channel pointer field indicates the differential channel the sense resistor is tied to for the RTD (see Table 27). Sense resistors are always measured differentially. Table 27. Sense Resistor Channel Pointer (1) RTD Type (2) SENSE RESISTOR CHANNEL POINTER The RTD type is determined by the first five input bits B31 to B27 as shown in Table 26. Linearization coefficients for RTD types PT-10, PT-50, PT-100, PT-200, PT-500, PT-1000, and NI-120 with selectable common curves (α = 0.003850, α = 0.003911, α = 0.003916, and α = 0.003926) are built into the device. If custom RTDs are used, RTD Custom can be selected. In this case, user specific data can be stored in the on-chip RAM starting at the address defined by the custom RTD data pointers. Table 26. RTD Type (1) RTD TYPE B26 B25 B24 B23 B22 SENSE RESISTOR CHANNEL 0 0 0 0 0 Invalid 0 0 0 0 1 Invalid 0 0 0 1 0 CH2-CH1 0 0 0 1 1 CH3-CH2 0 0 1 0 0 CH4-CH3 0 0 1 0 1 CH5-CH4 0 0 1 1 0 CH6-CH5 0 0 1 1 1 CH7-CH6 0 1 0 0 0 CH8-CH7 0 1 0 0 1 CH9-CH8 0 1 0 1 0 CH10-CH9 0 1 0 1 1 CH11-CH10 B31 B30 B29 B28 B27 RTD TYPE 0 1 1 0 0 CH12-CH11 0 1 0 1 0 RTD PT-10 0 1 1 0 1 CH13-CH12 0 1 0 1 1 RTD PT-50 0 1 1 1 0 CH14-CH13 0 1 1 0 0 RTD PT-100 0 1 1 1 1 CH15 -CH14 0 1 1 0 1 RTD PT-200 1 0 0 0 0 CH16-CH15 0 1 1 1 0 RTD PT-500 1 0 0 0 1 CH17-CH16 0 1 1 1 1 RTD PT-1000 1 0 0 1 0 CH18-CH17 1 0 0 0 0 RTD 1000 (α=0.00375) 1 0 0 1 1 CH19-CH18 1 0 0 0 1 RTD NI-120 1 0 1 0 0 CH20-CH19 1 0 0 1 0 RTD Custom 28 All Other Combinations Invalid 2983fc For more information www.linear.com/LTC2983 LTC2983 APPLICATIONS INFORMATION (3) Sensor Configuration The sensor configuration field is used to define various RTD properties. Configuration bits B20 and B21 determine if the RTD is a 2, 3, or 4 wire type (see Table 28). The simplest configuration is the 2-wire configuration. While this setup is simple, parasitic errors due to IR drops in the leads result in systematic temperature errors. The 3-wire configuration cancels RTD lead resistance errors (if the lines are equal resistance) by applying two matched current sources to the RTD, one per lead. Mismatches in the two current sources are removed through transparent background calibration. 4-wire RTDs remove unbalanced RTD lead resistance by measuring directly across the sensor using a high impedance Kelvin sensing. 4-wire measurements with Kelvin RSENSE are useful in applications where sense resistor wiring parasitics can lead to errors; this is especially useful for low resistance PT-10 type RTDs. In this case, both the RTD and sense resistor have Kelvin sensing connections. The next sensor configuration bits (B18 and B19) determine the excitation current mode. These bits are used to enable RSENSE sharing, where one sense resistor is used for multiple 2-, 3-, and/or 4-wire RTDS. In this case, the RTD ground connection is internal and each RTD points to the same RSENSE channel. Table 28. RTD Sensor Configuration Selection (3) SENSE CONFIGURATION MEASUREMENT MODE BENEFITS RTDs CANCELS RTD CANCELS RTD CANCELS CANCELS CURRENT SENSE POSSIBLE MATCHED MISMATCH PARASITIC RSENSE NUMBER EXCITATION NUMBER GROUND SOURCE RESISTOR PER LEAD LEAD THERMOCOUPLE LEAD OF WIRES MODE OF WIRES CONNECTION ROTATION SHARING DEVICE RESISTANCE RESISTANCE EFFECTS RESISTANCE B21 B20 B19 B18 0 0 0 0 2-Wire 0 0 0 1 2-Wire 0 1 0 0 3-Wire External No No 5 Internal No Yes 9 External No No 5 • Internal No Yes 9 • No No 4 • 0 1 0 1 3-Wire 0 1 1 X Reserved 1 0 0 0 4-Wire External 1 0 0 1 4-Wire Internal No Yes 6 • • 1 0 1 0 4-Wire Internal Yes Yes 6 • • 1 0 1 1 Reserved 1 1 0 0 4-Wire, Kelvin RSENSE External No No 4 • • • 1 1 0 1 4-Wire, Kelvin RSENSE Internal No Yes 5 • • • 1 1 1 0 4-Wire, Kelvin RSENSE Internal Yes Yes 5 • • 1 1 1 1 Reserved • • • • 2983fc For more information www.linear.com/LTC2983 29 LTC2983 APPLICATIONS INFORMATION Bits B18 and B19 are also used to enable excitation current rotation to automatically remove parasitic thermocouple effects. Parasitic thermocouple effects may arise from the physical connected between the RTD and the measurement instrument. This mode is available for all 4-wire configurations using internal current source excitation. (4) Excitation Current The next field in the channel assignment word (B17 to B14) controls the magnitude of the excitation current applied to the RTD (see Table 29). The current selected is the total current flowing through the RTD independent of the wiring configuration. The RSENSE current is 2x the sensor excitation current for 3-wire RTDs. In order to prevent soft or hard faults, select a current such that the maximum voltage drop across the sensor or sense resistor is nominally 1.0V. For example, if RSENSE is 10kΩ and the RTD is a PT-100, select an excitation current of 100µA for 2-wire and 4-wire RTDs and select 50µA for a 3-wire RTD. Alternatively, using a 1kΩ sense resistor with a PT-100 RTD allows 500µA excitation for any wiring configuration. Table 29. Total Excitation Current for All RTD Wire Types (4) EXCITATION CURRENT B17 B16 B15 B14 CURRENT 0 0 0 0 Reserved 0 0 0 1 5μA 0 0 1 0 10μA 0 0 1 1 25μA 0 1 0 0 50μA 0 1 0 1 100µA 0 1 1 0 250µA 0 1 1 1 500µA 1 0 0 0 1mA (5) RTD Curve Bits B13 and B12 set the RTD curve used and the corresponding Callendar-Van Dusen constants (shown in Table 30). (6) Custom RTD Data Pointer In the case where an RTD not listed in Table 30 is used, a custom RTD table may be entered into the LTC2983. See Custom RTD section near the end of this data sheet for more information. Table 30. RTD Curves: RT = R0 • (1 + a • T + b • T2 + (T – 100°C) • c • T3) for T < 0°C, RT = R0 • (1 + a • T + b • T2) for T > 0°C (5) CURVE B13 B12 CURVE ALPHA 0 0 European Standard 0 1 American 1 0 Japanese 1 1 ITS-90 X X RTD1000-375 X X *NI-120 a b c 0.00385 3.908300E-03 –5.775000E-07 –4.183000E-12 0.003911 3.969200E-03 –5.849500E-07 –4.232500E-12 0.003916 3.973900E-03 –5.870000E-07 –4.400000E-12 0.003926 3.984800E-03 –5.870000E-07 –4.000000E-12 0.00375 3.810200E-03 –6.018880E-07 –6.000000E-12 N/A N/A N/A N/A *NI-120 uses table based data. 30 2983fc For more information www.linear.com/LTC2983 LTC2983 APPLICATIONS INFORMATION is a hard error and –999°C or °F is reported. In the case of an excessive noise event, the device should recover and the following conversions will be valid if the noise was a random infrequent event. Bits D29 and D28 are not used for RTDs. Bits D27 and D26 indicate over or under temperature limits (see Table 32). The calculated temperature is reported, but the accuracy may be compromised. Bit D25 indicates the absolute voltage measured by the ADC is beyond its normal operating range. If an RTD is used as the cold junction element, any hard or soft error is also flagged in the thermocouple result. Fault Reporting – RTD Each sensor type has unique fault reporting mechanism indicated in the most significant byte of the data output word. Table 31 shows faults reported in the measurement of RTDs. Bit D31 indicates the RTD or RSENSE is open, shorted, or not plugged in. This is a hard fault and –999°C or °F is reported. Bit D30 indicates a bad ADC reading. This can be a result of either a broken (open) sensor or an excessive noise event (ESD or static discharge into the sensor path). This Table 31. RTD Fault Reporting BIT FAULT D31 Sensor Hard Fault ERROR TYPE Hard DESCRIPTION Open or Short RTD or RSENSE OUTPUT RESULT –999°C or °F D30 Hard ADC-Out-of-Range Hard Bad ADC Reading (Could Be Large External Noise Event) –999°C or °F D29 Not Used for RTDs N/A Always 0 Valid Reading D28 Not Used for RTDs N/A Always 0 Valid Reading D27 Sensor Over Range Soft T > High Temp Limit (See Table 32) Suspect Reading D26 Sensor Under Range Soft T < Low Temp Limit (See Table 32) Suspect Reading D25 ADC Out-of-Range Soft ADC Absolute Input Voltage Is Beyond ±1.125 • VREF/2 Suspect Reading D24 Valid N/A Result Valid (Should Be 1) Discard Results if 0 Valid Reading Table 32. Voltage and Resistance Ranges RTD TYPE MIN Ω MAX Ω LOW TEMP LIMIT °C HIGH TEMP LIMIT °C PT-10 1.95 34.5 –200 850 PT-50 9.75 172.5 –200 850 PT-100 19.5 345 –200 850 PT-200 39 690 –200 850 PT-500 97.5 1725 –200 850 PT-1000 195 3450 –200 850 NI-120 66.6 380.3 –80 260 Custom Table Lowest Table Entry Highest Table Entry Lowest Table Entry Highest Table Entry 2983fc For more information www.linear.com/LTC2983 31 LTC2983 APPLICATIONS INFORMATION Sense Resistor Table 33. Sense Resistor Channel Assignment Word Measurement Class (1) SENSOR TYPE (2) SENSE RESISTOR VALUE (Ω) FIGURE 36 FIGURE 40 31 30 29 28 27 26 25 24 23 22 21 20 19 18 17 16 15 14 13 12 11 10 9 Sense Resistor Type = 29 8 7 6 5 4 3 2 1 0 Sense Resistor Value (17, 10) Up to ≈ 131,072Ω with 1/1024Ω Resolution Channel Assignment can be tied directly to 2-lead RTD elements. The disadvantages of this topology are errors due to parasitic lead resistance. If sharing is not selected (1 RSENSE per RTD), then CHRTD should be grounded. The ground connection should be removed if sharing is enabled (1 RSENSE for multiple RTDs). For each sense resistor tied to the LTC2983, a 32-bit channel assignment word is programmed into a memory location corresponding to the channel the sensor is tied to (see Table 33). This word includes (1) sense resistor selection and (2) sense resistor value. 2ND TERMINAL TIES TO SENSE RESISTOR (CHRSENSE) (1) Sensor Type EXCITATION CURRENT FLOW The sense resistor is selected by setting the first 5 input bits, B31 to B27, to 11101 (see Table 34). 2 CHRTD-1 1 CHRTD CHANNEL = CH RTD (2≤ RTD ≤ 20) ASSIGNMENT OPTIONAL GND, REMOVE FOR RSENSE SHARING 2983 F07 Table 34. Sense Resistor Selection Figure 7. 2-Wire RTD Channel Assignment Convention (1) SENSOR TYPE B31 B30 B29 B28 B27 SENSOR TYPE 1 1 1 0 1 Sense Resistor Sense resistor channel assignments follow the general convention shown in Figure 8. The sense resistor is tied between CHRSENSE and CHRSENSE-1, where CHRSENSE is tied to the 2nd terminal of the RTD. Channel assignment data (see Table 33) is mapped into a memory location corresponding to CHRSENSE. (2) Sense Resistor Value The last field in the channel assignment word (B26 to B0) sets the value of the sense resistor within the range 0 to 131,072Ω with 1/1024Ω precision (see Table 35). The top 17 bits (B26 to B10) create the integer and bits B9 to B0 create the fraction of the sense resistor value. CHRSENSE-1 EXCITATION CURRENT FLOW Example: 2-Wire RTD RSENSE CHRSENSE CHANNEL = CH RSENSE (2≤ RSENSE ≤ 20) ASSIGNMENT 2983 F08 The simplest RTD configuration is the 2-wire configuration, 2-wire RTDs follow the general convention shown in Figure 7. They require only two connections per RTD and Figure 8. Sense Resistor Channel Assignment Convention for 2-Wire RTDs Table 35. Example Sense Resistor Values (2) SENSE RESISTOR VALUE (Ω) B26 B25 B24 B23 B22 B21 B20 B19 B18 B17 B16 B15 B14 B13 B12 B11 B10 B9 B8 B7 Example R 216 215 214 213 212 211 210 29 B6 B5 B4 B3 B2 B1 B0 28 27 26 25 24 23 22 21 20 2–1 2–2 2–3 2–4 2–5 2–6 2–7 2–8 2–9 2–10 0 0 1 0 0 0 0 10,000.2Ω 0 0 0 1 0 0 1 1 1 0 99.99521kΩ 1 1 0 0 0 0 1 1 0 1 0 0 1 1 0 1 1 0 0 1 1 0 1 0 1 1 1 1.0023kΩ 0 0 0 0 0 0 0 1 1 1 1 1 0 1 0 1 0 0 1 0 0 1 1 0 0 1 1 32 0 0 1 1 0 0 1 1 0 1 2983fc For more information www.linear.com/LTC2983 LTC2983 APPLICATIONS INFORMATION (see Table 37). The sense resistor is assigned to CH16. The user-programmable value of this resistor is 5001.5Ω. 32 bits of binary configuration data are mapped directly into memory locations 0x23C to 0x23F (see Table 38). Example: 2-Wire RTDs with Shared RSENSE Figure 9 shows a typical temperature measurement system using multiple 2-wire RTDs. In this example, a PT-1000 RTD ties to CH17 and CH18 and an NI-120 RTD ties to CH19 and CH20. Using this configuration, the LTC2983 can digitize up to nine 2-wire RTDs with a single sense resistor. A conversion is initiated on CH18 by writing 10010010 into memory location 0x000. Once the conversion is complete, the INTERRUPT pin goes HIGH and memory location 0x000 becomes 01010010. The resulting temperature in °C can be read from memory locations 0x054 to 0x057 (corresponding to CH18). A conversion can be initiated and read from CH20 in a similar fashion. RTD #1 sensor type and configuration data are assigned to CH18. 32 bits of binary configuration data are mapped directly into memory locations 0x244 to 0x247 (see Table 36). RTD #2 sensor type and configuration data are assigned to CH20. 32-bits of binary configuration data are mapped directly into memory locations 0x24C to 0x24F CH15 RSENSE 5001.5Ω 0.01µF SENSE RESISTOR ASSIGNED TO CH16 (CHRSENSE=16) CHANNEL ASSIGNMENT MEMORY LOCATIONS 0x23C TO 0x23F CH16 0.01µF 2 CH17 0.01µF 2-WIRE PT-1000 1 RTD #1 ASSIGNED TO CH18 (CHRTD=18) CHANNEL ASSIGNMENT MEMORY LOCATIONS 0x244 TO 0x247 RESULT MEMORY LOCATIONS 0x054 TO 0x057 CH18 0.01µF 2 CH19 0.01µF 2-WIRE NI-120 1 RTD #2 ASSIGNED TO CH20 (CHRTD=20) CHANNEL ASSIGNMENT MEMORY LOCATIONS 0x24C TO 0x24F RESULT MEMORY LOCATIONS 0x05C TO 0x05F CH20 0.01µF 2983 F09 Figure 9. Shared 2-Wire RTD Example Table 36. Channel Assignment Data for 2-Wire RTD #1 (PT-1000, RSENSE on CH16, 2-Wire, Shared RSENSE, 10µA Excitation Current, α = 0.003916 Curve) CONFIGURATION DESCRIPTION # BITS FIELD (1) RTD TYPE BINARY DATA MEMORY ADDRESS 0x244 PT-1000 5 01111 0 1 1 1 1 CH16 5 10000 (3) Sensor Configuration 2-Wire with Shared RSENSE 4 0001 (4) Excitation Current 10µA 4 0010 Japanese, α = 0.003916 2 10 Not Custom 12 000000000000 (2) Sense Resistor Channel Pointer (5) Curve (6) Custom RTD Data Pointer MEMORY ADDRESS 0x245 MEMORY ADDRESS 0x246 MEMORY ADDRESS 0x247 1 0 0 0 0 0 0 0 1 0 0 1 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 2983fc For more information www.linear.com/LTC2983 33 LTC2983 APPLICATIONS INFORMATION Table 37. Channel Assignment Data for 2-Wire RTD #2 (NI-120, RSENSE on CH16, 2-Wire, Shared RSENSE, 100µA Excitation Current) CONFIGURATION DESCRIPTION # BITS FIELD (1) RTD TYPE BINARY DATA MEMORY ADDRESS 0x24C NI-120 5 10001 1 0 0 0 1 CH16 5 10000 (3) Sensor Configuration 2-Wire with Shared RSENSE 4 0001 (4) Excitation Current 100µA 4 0101 (5) Curve European α = 0.00385 2 00 (6) Custom RTD Data Pointer Not Custom 12 000000000000 (2) Sense Resistor Channel Pointer MEMORY ADDRESS 0x24D MEMORY ADDRESS 0x24E MEMORY ADDRESS 0x24F 1 0 0 0 0 0 0 0 1 0 1 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 Table 38. Channel Assignment Data for Sense Resistor (Value = 5001.5Ω) CONFIGURATION DESCRIPTION # BITS FIELD (1) Sensor Type Sense Resistor 5 (2) Sense Resistor Value 5001.5Ω 27 BINARY DATA MEMORY MEMORY ADDRESS 0x23C ADDRESS 0x23D MEMORY ADDRESS 0x23E MEMORY ADDRESS 0x23F 11101 1 1 1 0 1 000010011100010011000000000 0 0 0 0 1 00 1 1 1 0 0 0 1 0 0 1 1 0 0 0 0 0 0 0 0 0 Example: 3-Wire RTD 3-wire RTD channel assignments follow the general convention shown in Figure 10. Terminals 1 and 2 tie to the input/excitation current sources and terminal 3 connects to the sense resistor. Channel assignment data is mapped to memory locations corresponding to CHRTD. CHRSENSE 3 EXCITATION CURRENT FLOW 2 3RD TERMINAL TIES TO SENSE RESISTOR (OPTIONAL GND, REMOVE FOR RSENSE SHARING) CHRTD-1 CHRSENSE-1 1 CHRTD CHANNEL = CH RTD (2≤ RTD ≤ 20) ASSIGNMENT 2983 F10 Figure 10. 3-Wire RTD Channel Assignment Convention 34 Sense resistor channel assignments follow the general convention shown in Figure 11. The sense resistor is tied between CHRSENSE and CHRSENSE-1, where CHRSENSE is tied to the 3rd terminal of the RTD and CHRSENSE-1 is tied to ground (or left floating for RSENSE sharing). Channel assignment data (see Table 33) is mapped into the memory location corresponding to CHRSENSE. 2x EXCITATION CURRENT FLOW RSENSE CHRSENSE CHANNEL = CH RSENSE (2≤ RSENSE ≤ 20) ASSIGNMENT 2983 F11 Figure 11. 3-Wire Sense Resistor Channel Assignment Convention for 3-Wire RTDs 2983fc For more information www.linear.com/LTC2983 LTC2983 APPLICATIONS INFORMATION Figure 12 shows a typical temperature measurement system using a 3-wire RTD. In this example, a 3-wire RTD’s terminals tie to CH9, CH8, and CH7. The sense resistor ties to CH7 and CH6. The sense resistor and RTD connect together at CH7. errors due to thermocouple effects or mismatched lead resistances. The RTD sensor type and configuration data are assigned to CH9. 32 bits of binary configuration data are mapped directly into memory locations 0x220 to 0x223 (see Table 39). The sense resistor is assigned to CH7. The user-programmable value of this resistor is 12150.39Ω. 32 bits of binary configuration data are mapped directly into memory locations 0x218 to 0x21B (see Table 40). The 3-wire RTD reduces the errors associated with parasitic lead resistance by applying excitation current to each RTD input. This first order cancellation removes matched lead resistance errors. This cancellation does not remove CH6 0.01µF RSENSE 12,150.39Ω RSENSE ASSIGNED TO CH7 (CHSENSE=7) CHANNEL ASSIGNMENT MEMORY LOCATIONS 0x218 TO 0x21B CH7 0.01µF 3 2 CH8 0.01µF 3-WIRE PT-200 3-WIRE RTD ASSIGNED TO CH9 (CHRTD=9) CHANNEL ASSIGNMENT MEMORY LOCATIONS 0x220 TO 0x223 RESULT MEMORY LOCATIONS 0x030 TO 0x033 CH9 1 0.01µF 2983 F12 Figure 12. 3-Wire RTD Example Table 39. Channel Assignment Data for 3-Wire RTD (PT-200, RSENSE on CH7, 3-Wire, 50µA Excitation Current, α = 0.003911 Curve) CONFIGURATION DESCRIPTION # BITS FIELD (1) RTD TYPE BINARY DATA MEMORY ADDRESS 0x220 PT-200 5 01101 0 1 1 0 1 CH7 5 00111 (3) Sensor Configuration 3-Wire 4 0100 (4) Excitation Current 50µA 4 0100 American, α = 0.003911 2 01 Not Custom 12 000000000000 (2) Sense Resistor Channel Pointer (5) Curve (6) Custom RTD Data Pointer MEMORY ADDRESS 0x221 MEMORY ADDRESS 0x222 MEMORY ADDRESS 0x223 0 0 1 1 1 0 1 0 0 0 1 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 Table 40. Channel Assignment Data for Sense Resistor (Value = 12150.39Ω) CONFIGURATION DESCRIPTION # BITS FIELD (1) Sensor Type Sense Resistor (2) Sense Resistor 12150.39Ω Value 5 27 BINARY DATA MEMORY ADDRESS 0x218 MEMORY ADDRESS 0x219 MEMORY ADDRESS 0x21A MEMORY ADDRESS 0x21B 11101 1 1 1 0 1 000101111011101100110001111 0 0 0 1 0 1 11 1 0 1 1 1 0 1 1 0 0 1 1 0 0 0 1 1 1 0 2983fc For more information www.linear.com/LTC2983 35 LTC2983 APPLICATIONS INFORMATION A conversion is initiated on CH9 by writing 10001001 into memory location 0x000 . Once the conversion is complete, the INTERRUPT pin goes HIGH and memory location 0x000 becomes 01001001. The resulting temperature in °C can be read from memory locations 0x030 to 0x033 (corresponding to CH9). Sense resistor channel assignments follow the general convention shown in Figure 14. The sense resistor is tied between CHRSENSE and CHSENSE-1, where CHRSENSE is tied to the 4th terminal of the RTD. Channel assignment data (see Table 33) is mapped into a memory location corresponding to CHRSENSE. Example: Standard 4-Wire RTD (No Rotation or RSENSE Sharing) Standard 4-wire RTD channel assignments follow the general convention shown in Figure 13. Terminal 1 is tied to ground, terminals 2 and 3 (Kelvin sensed signal) tie to CHRTD and CHRTD-1, and the 4th terminal ties to the sense resistor. Channel assignment data (see Table 25) is mapped to memory locations corresponding to CHRTD. CHRSENSE 4 EXCITATION CURRENT FLOW CHRSENSE-1 EXCITATION CURRENT FLOW RSENSE CHRSENSE CHANNEL = CH RSENSE (2≤ RSENSE ≤ 20) ASSIGNMENT 2983 F14 Figure 14. Sense Resistor Channel Assignment Convention for 4-Wire RTDs 4TH TERMINAL TIES TO SENSE RESISTOR (CHRSENSE) 3 CHRTD-1 2 CHRTD CHANNEL = CH RTD (2≤ RTD ≤ 20) ASSIGNMENT 1 2983 F13 Figure 13. 4-Wire RTD Channel Assignment Convention 36 2983fc For more information www.linear.com/LTC2983 LTC2983 APPLICATIONS INFORMATION Figure 15 shows a typical temperature measurement system using a 4-wire RTD. In this example, a 4-wire RTD’s terminals tie to GND, CH13, CH12, and CH11. The sense resistor ties to CH11 and CH10. The sense resistor and RTD share a common connection at CH11. The RTD sensor type and configuration data are assigned to CH13. 32 bits of binary configuration data are mapped directly into memory locations 0x230 to 0x233 (see Table 41). The sense resistor is assigned to CH11. The user programmable value of this resistor is 5000.2Ω. 32 bits of binary configuration data are mapped directly into memory locations 0x228 to 0x22B (see Table 42). A conversion is initiated on CH13 by writing 10001101 into the data byte at memory location 0x000. Once the conversion is complete, the INTERRUPT pin goes HIGH and memory location 0x000 becomes 01001101. The resulting temperature in °C can be read from memory locations 0x040 to 0x043 (corresponding to CH13). CH10 0.01µF RSENSE 5000.2Ω SENSE RESISTOR ASSIGNED TO CH11 (CHSENSE=11) CHANNEL ASSIGNMENT MEMORY LOCATIONS 0x228 TO 0x22B CH11 0.01µF 4 3 CH12 0.01µF 4-WIRE PT-1000 2 RTD ASSIGNED TO CH13 (CHRTD=13) CHANNEL ASSIGNMENT MEMORY LOCATIONS 0x230 TO 0x233 RESULT MEMORY LOCATIONS 0x040 TO 0x043 CH13 1 0.01µF 2983 F15 Figure 15. Standard 4-Wire RTD Example Table 41. Channel Assignment Data for 4-Wire RTD (PT-1000, RSENSE on CH11, Standard 4-Wire, 25µA Excitation Current, α = 0.00385 Curve) CONFIGURATION DESCRIPTION # BITS FIELD (1) RTD TYPE BINARY DATA MEMORY ADDRESS 0x230 PT-1000 5 01111 0 1 1 1 1 CH11 5 01011 (3) Sensor Configuration 4-Wire, No Rotate, No Share 4 1000 (4) Excitation Current 25µA 4 0011 (5) Curve European, α=0.00385 2 00 (6) Custom RTD Data Pointer Not Custom 12 000000000000 (2) Sense Resistor Channel Pointer MEMORY ADDRESS 0x231 MEMORY ADDRESS 0x232 MEMORY ADDRESS 0x233 0 1 0 1 1 1 0 0 0 0 0 1 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 Table 42. Channel Assignment Data for Sense Resistor (Value = 5000.2Ω) CONFIGURATION DESCRIPTION # BITS FIELD (1) Sensor Type Sense Resistor 5 (2) Sense Resistor Value 5000.2Ω 27 BINARY DATA MEMORY ADDRESS 0x228 MEMORY ADDRESS 0x229 MEMORY ADDRESS 0x22A MEMORY ADDRESS 0x22B 11101 1 1 1 0 1 000010011100010000011001100 0 0 0 0 1 0 0 1 1 1 0 0 0 1 0 0 00 0 1 1 0 0 1 1 0 0 2983fc For more information www.linear.com/LTC2983 37 LTC2983 APPLICATIONS INFORMATION Example: 4-Wire RTD with Rotation One method to improve the accuracy of an RTD over the standard 4-wire implementation is by rotating the excitation current source. Parasitic thermocouple effects are automatically removed through autorotation. In order to perform autorotation, the 1st terminal of the RTD ties to CHRTD+1 instead of GND, as in the standard case. This allows the LTC2983 to automatically change the direction of the current source without the need for additional external components. 4-wire RTD with rotation channel assignments follow the general convention shown in Figure 16. Terminal 1 is tied to CHRTD+1, terminals 2 and 3 (Kelvin sensed signal) tie to CHRTD and CHRTD-1, and the 4th terminal ties to the sense resistor. Channel assignment data (see Table 25) is mapped to memory locations corresponding to CHRTD. Sense resistor channel assignments follow the general convention shown in Figure 17. The sense resistor is tied between CHRSENSE and CHRSENSE-1, where CHRSENSE is tied to the 4th terminal of the RTD. Channel assignment data is mapped into a memory location corresponding to CHRSENSE. CHRSENSE-1 EXCITATION CURRENT FLOW RSENSE CHRSENSE CHANNEL = CH RSENSE (2≤ RSENSE ≤ 20) ASSIGNMENT 2983 F17 Figure 17. Sense Resistor Channel Assignment Convention for 4-Wire RTDs with Rotation CHRSENSE 4TH TERMINAL TIES TO SENSE RESISTOR 4 EXCITATION CURRENT FLOW 3 CHRTD–1 2 CHRTD CHANNEL = CH RTD (2≤ RTD ≤ 19) ASSIGNMENT 1 CHRTD+1 2983 F16 Figure 16. 4-Wire RTD Channel Assignment Convention 38 2983fc For more information www.linear.com/LTC2983 LTC2983 APPLICATIONS INFORMATION Figure 18 shows a typical temperature measurement system using a rotating 4-wire RTD. In this example a 4-wire RTD’s terminals tie to CH17, CH16, CH15, and CH6. The sense resistor is tied to CH6 and CH5. The sense resistor and RTD connect together at CH6. The RTD sensor type and configuration data are assigned to CH16. 32 bits of binary configuration data are mapped directly into memory locations 0x23C to 0x23F (see Table 43). The sense resistor is assigned to CH6. The user programmable value of this resistor is 10.0102kΩ. 32 bits of binary configuration data are mapped directly into memory locations 0x214 to 0x217 (see Table 44). A conversion is initiated on CH16 by writing 10010000 into memory location 0x000. Once the conversion is complete, the INTERRUPT pin goes HIGH and memory location 0x000 becomes 01010000. The resulting temperature in °C can be read from memory locations 0x04C to 0x04F (corresponding to CH16). CH5 0.01µF RSENSE 10.0102k SENSE RESISTOR ASSIGNED TO CH6 (CHSENSE=6) CHANNEL ASSIGNMENT MEMORY LOCATIONS 0x214 TO 0x217 CH6 0.01µF 4 3 CH15 0.01µF PT-100 2 RTD ASSIGNED TO CH16 (CHRTD=16) CHANNEL ASSIGNMENT MEMORY LOCATIONS 0x23C TO 0x23F RESULT MEMORY LOCATIONS 0x04C TO 0x04F CH16 1 0.01µF CH17 0.01µF 2983 F18 Figure 18. Rotating 4-Wire RTD Example Table 43. Channel Assignment Data for Rotating 4-Wire RTD (PT-100, RSENSE on CH6, Rotating 4-Wire, 100µA Excitation Current, α = 0.003911 Curve) CONFIGURATION DESCRIPTION # BITS FIELD (1) RTD TYPE BINARY DATA MEMORY ADDRESS 0x23C PT-100 5 01100 0 1 1 0 0 CH6 5 00110 (3) Sensor Configuration 4-Wire with Rotation 4 1010 (4) Excitation Current 100µA 4 0101 (5) Curve American, α=0.003911 2 01 (6) Custom RTD Data Pointer Not Custom 12 000000000000 (2) Sense Resistor Channel Pointer MEMORY ADDRESS 0x23D MEMORY ADDRESS 0x23E MEMORY ADDRESS 0x23F 0 0 1 1 0 1 0 1 0 0 1 0 1 0 1 0 0 0 0 0 0 0 0 0 0 0 0 Table 44. Channel Assignment Data for Sense Resistor (Value = 10.0102kΩ) CONFIGURATION DESCRIPTION # BITS FIELD (1) Sensor Type Sense Resistor 5 (2) Sense Resistor Value 10.0102kΩ 27 BINARY DATA MEMORY ADDRESS 0x214 MEMORY ADDRESS 0x215 MEMORY ADDRESS 0x216 MEMORY ADDRESS 0x217 11101 1 1 1 0 1 000100111000110100011001100 0 0 0 1 0 0 1 1 1 0 0 0 1 1 0 1 0 0 0 1 1 0 0 1 1 0 0 2983fc For more information www.linear.com/LTC2983 39 LTC2983 APPLICATIONS INFORMATION Example: Multiple 4-Wire RTDs with Shared RSENSE topology supports both rotated and non-rotated RTD excitations. Channel assignment data for each sensor is shown in Tables 45 to 47. Figure 19 shows a typical temperature measurement system using two 4-wire RTDs with a shared RSENSE. The LTC2983 can support up to six 4-wire RTDs with a single sense resistor. In this example, the first 4-wire RTD’s terminals tie to CH17, CH16, CH15, and CH6 and the 2nd ties to CH20, CH19, CH18, and CH6. The sense resistor ties to CH5 and CH6. The sense resistor and both RTDs connect together at CH6. This channel assignment convention is identical to that of the rotating RTD. This A conversion is initiated on CH16 by writing 10010000 into memory location 0x000. Once the conversion is complete, the INTERRUPT pin goes HIGH and memory location 0x000 becomes 01010000. The resulting temperature in °C can be read from memory locations 0x04C to 0x04F (corresponding to CH16). A conversion can be initiated and read from CH19 in a similar fashion. CH5 0.01µF RSENSE 10k SENSE RESISTOR ASSIGNED TO CH6 (CHSENSE=6) CHANNEL ASSIGNMENT MEMORY LOCATIONS 0x214 TO 0x217 CH6 0.01µF 4 3 CH15 0.01µF 4-WIRE PT-100 2 RTD #1 ASSIGNED TO CH16 (CHRTD=16) CHANNEL ASSIGNMENT MEMORY LOCATIONS 0x23C TO 0x23F RESULT MEMORY LOCATIONS 0x04C TO 0x04F CH16 1 0.01µF CH17 0.01µF 4 3 CH18 0.01µF 4-WIRE PT-500 2 RTD #2 ASSIGNED TO CH19 (CHRTD=19) CHANNEL ASSIGNMENT MEMORY LOCATIONS 0x248 TO 0x24B RESULT MEMORY LOCATIONS 0x058 TO 0x05B CH19 1 0.01µF CH20 0.01µF 2983 F19 Figure 19. Shared RSENSE 4-Wire RTD Example Table 45. Channel Assignment Data for 4-Wire RTD #1 (PT-100, RSENSE on CH6, 4-Wire, Shared RSENSE, Rotated 100µA Excitation Current, α = 0.003926 Curve) CONFIGURATION DESCRIPTION # BITS FIELD (1) RTD TYPE BINARY DATA MEMORY ADDRESS 0x23C PT-100 5 01100 0 1 1 0 0 CH6 5 00110 (3) Sensor Configuration 4-Wire Rotated 4 1010 (4) Excitation Current 100µA 4 0101 (5) Curve ITS-90, α=0.003926 2 11 (6) Custom RTD Data Pointer Not Custom 12 000000000000 (2) Sense Resistor Channel Pointer 40 MEMORY ADDRESS 0x23D MEMORY ADDRESS 0x23E MEMORY ADDRESS 0x23F 0 0 1 1 0 1 0 1 0 0 1 0 1 1 1 0 0 0 0 0 0 0 0 0 0 0 0 2983fc For more information www.linear.com/LTC2983 LTC2983 APPLICATIONS INFORMATION Table 46. Channel Assignment Data for 4-Wire RTD #2 (PT-500, RSENSE on CH6, 4-Wire, Rotated 50µA Excitation Current, α = 0.003911 Curve) CONFIGURATION DESCRIPTION # BITS FIELD (1) RTD TYPE BINARY DATA MEMORY ADDRESS 0x248 PT-500 5 01110 0 1 1 1 0 CH6 5 00110 (3) Sensor Configuration 4-Wire Shared, No Rotation 4 1001 (4) Excitation Current 50µA 4 0100 (5) Curve American, α=0.003911 2 01 (6) Custom RTD Data Pointer Not Custom 12 000000000000 (2) Sense Resistor Channel Pointer MEMORY ADDRESS 0x249 MEMORY ADDRESS 0x24A MEMORY ADDRESS 0x24B 0 0 1 1 0 1 0 0 1 0 1 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 Table 47. Channel Assignment Data for Sense Resistor (Value = 10.000kΩ) CONFIGURATION DESCRIPTION # BITS FIELD (1) Sensor Type Sense Resistor 5 (2) Sense Resistor Value 10.000kΩ 27 BINARY DATA MEMORY ADDRESS 0x214 MEMORY ADDRESS 0x215 MEMORY ADDRESS 0x216 MEMORY ADDRESS 0x217 11101 1 1 1 0 1 000100111000100000000000000 Example: 4-Wire RTD with Kelvin RSENSE It is possible to cancel the parasitic lead resistance in the sense resistors by configuring the 4-wire RTD with a 4-wire (Kelvin connected) sense resistor. This is useful when using a PT-10 or PT-50 with a small valued RSENSE or when the sense resistor is remotely located or in applications requiring extreme precision. 0 0 0 10 0 1 1 1 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 00 The 4-wire RTD channel assignments follow the general conventions previously defined (Figures 14 and 16) for a standard 4-wire RTD. The sense resistor follows the convention shown in Figure 20. CHRSENSE–2 4 EXCITATION CURRENT FLOW 3 CHRSENSE–1 2 CHRSENSE RSENSE CHANNEL = CH RSENSE (3≤ RSENSE ≤ 20) ASSIGNMENT 1 TIES TO RTD TERMINAL 4 2983 F20 Figure 20. Sense Resistor with Kelvin Connections Channel Assignment Convention 2983fc For more information www.linear.com/LTC2983 41 LTC2983 APPLICATIONS INFORMATION Figure 21 shows a typical temperature measurement system using a 4-wire RTD with a Kelvin connected RSENSE. In this example, the 4-wire RTD’s terminals tie to CH17, CH16, CH15, and CH6. The sense resistor ties to CH6, CH5, and CH4 and excitation current is applied to CH4 and CH17. The sense resistor’s nominal value is 1kΩ in order to accommodate a 1mA excitation current. The sense resistor and RTD connect together at CH6. This topology supports both rotated, shared and standard 4-wire RTD topologies. If rotated or shared configuration are not used then terminal 1 of the RTD is tied to ground instead of CH17, freeing up one input channel. Channel assignment data is shown in Tables 48 and 49. A conversion is initiated on CH16 by writing 10010000 into memory location 0x000. Once the conversion is complete, the INTERRUPT pin goes HIGH and memory location 0x000 becomes 01010000 (see Table 6). The resulting temperature in °C can be read from memory locations 0x04C to 0x04F (corresponding to CH16). CH4 0.01µF 4 3 CH5 SENSE RESISTOR ASSIGNED TO CH6 (CHSENSE=6) CHANNEL ASSIGNMENT MEMORY LOCATIONS 0x214 TO 0x217 0.01µF RSENSE 1k 2 1 CH6 0.01µF 4 3 CH15 0.01µF 4-WIRE PT-10 2 1 RTD ASSIGNED TO CH16 (CHRTD=16) CHANNEL ASSIGNMENT MEMORY LOCATIONS 0x23C TO 0x23F RESULTS MEMORY LOCATIONS 0x04C TO 0x04F CH16 0.01µF CH17 0.01µF 2983 F21 Figure 21. Sense Resistor with Kelvin Connections Example Table 48. Channel Assignment Data for 4-Wire RTD with Kelvin Connected RSENSE (PT-10, RSENSE on CH6, 4-Wire, Kelvin RSENSE with Rotated 1mA Excitation Current, α = 0.003916 Curve) CONFIGURATION FIELD DESCRIPTION (1) RTD TYPE (6) Custom RTD Data Pointer MEMORY ADDRESS 0x23C 5 01010 0 1 0 1 0 CH6 5 00110 4-Wire Kelvin RSENSE and Rotation 4 1110 (4) Excitation Current (5) Curve BINARY DATA PT-10 (2) Sense Resistor Channel Pointer (3) Sensor Configuration # BITS 1mA 4 1000 Japanese, α=0.003916 2 10 Not Custom 12 000000000000 MEMORY ADDRESS 0x23D MEMORY ADDRESS 0x23E MEMORY ADDRESS 0x23F 0 0 1 1 0 1 1 1 0 1 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 Table 49. Channel Assignment Data for Sense Resistor (Value = 1000Ω) CONFIGURATION DESCRIPTION # BITS FIELD (1) Sensor Type Sense Resistor 5 (2) Sense Resistor Value 27 42 1000Ω BINARY DATA MEMORY ADDRESS 0x214 MEMORY ADDRESS 0x215 MEMORY ADDRESS 0x216 MEMORY ADDRESS 0x217 11101 1 1 1 0 1 000000011111010000000000000 0 0 0 0 0 0 0 1 1 1 1 1 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 2983fc For more information www.linear.com/LTC2983 LTC2983 APPLICATIONS INFORMATION THERMISTOR MEASUREMENTS (1) Thermistor Type Channel Assignment – Thermistor The thermistor type is determined by the first five input bits (B31 to B27) as shown in Table 51. Linearization coefficients based on Steinhart-Hart equation for commonly used Thermistor types 44004/44033, 44005/44030, 44006/44031, 44007/44034, 44008/44032 and YSI-400 are built into the device. If other custom thermistors are used, Thermistor Custom Steinhart-Hart or Thermistor Custom Table (temperature vs resistance) can be selected. In this case, user specific data can be stored in the on-chip RAM starting at the address defined in Thermistor Custom Steinhart-Hart or Thermistor Custom Table address pointers. For each thermistor tied to the LTC2983, a 32-bit channel assignment word is programmed into a memory location corresponding to the channel the sensor is tied to (see Table 50). This data includes (1) thermistor type, (2) sense resistor channel pointer, (3) sensor configuration, (4) excitation current, (5) Steinhart-Hart address pointer or custom table address pointer. Table 50. Thermistor Channel Assignment Word (1) THERMISTOR (2) SENSE RESISTOR TYPE CHANNEL POINTER TABLE 51 Type = 19 to 27 (4) EXCITATION CURRENT (5) CUSTOM THERMISTOR DATA POINTER TABLE 52 TABLE 53 TABLES 76, 77, 78, 80, 81 TABLE 27 Measurement Class 31 30 29 28 27 26 25 24 23 22 Thermistor (3) SENSOR CONFIGURATION RSENSE Channel Pointer [4:0] 21 SGL = 1 DIFF = 0 20 19 Excitation Mode 18 17 16 15 14 13 12 11 10 9 8 7 6 5 4 3 2 1 0 Excitation Current Not Used [3:0] 0 0 0 Custom Address Custom Length – 1 [5:0] [5:0] Table 51. Thermistor Type: 1/T = A + B • ln(R) + C • ln(R)2 + D • ln(R)3 + E • ln(R)4 + F •ln(R)5 B31 B30 B29 B28 B27 THERMISTOR TYPE A B C D E F 1 0 0 1 1 Thermistor 44004/44033 2.252kΩ at 25°C 1.46800E-03 2.38300E-04 0 1.00700E-07 0 0 1 0 1 0 0 Thermistor 44005/44030 3kΩ at 25°C 1.40300E-03 2.37300E-04 0 9.82700E-08 0 0 1 0 1 0 1 Thermistor 44007/44034 5kΩ at 25°C 1.28500E-03 2.36200E-04 0 9.28500E-08 0 0 1 0 1 1 0 Thermistor 44006/44031 10kΩ at 25°C 1.03200E-03 2.38700E-04 0 1.58000E-07 0 0 1 0 1 1 1 Thermistor 44008/44032 30kΩ at 25°C 9.37600E-04 2.20800E-04 0 1.27600E-07 0 0 1 1 0 0 0 Thermistor YSI-400 2.252kΩ at 25°C 1.47134E-03 2.37624E-04 0 1.05034E-07 0 0 1 1 0 0 1 Spectrum 1003k 1kΩ at 25°C 1.445904E-3 2.68399E-04 0 1.64066E-07 0 0 1 1 0 1 0 Thermistor Custom Steinhart-Hart user input user input user input user input user input user input 1 1 0 1 1 Thermistor Custom Table not used not used not used not used not used not used 2983fc For more information www.linear.com/LTC2983 43 LTC2983 APPLICATIONS INFORMATION (2) Sense Resistor Channel Pointer (4) Excitation Current Thermistor measurements are performed ratiometrically relative to a known RSENSE resistor. The sense resistor channel pointer field indicates the differential channel the sense resistor is tied to for the current thermistor (see Table 27). The next field in the channel assignment word (B18 to B15) controls the magnitude of the excitation current applied to the thermistor (see Table 53). In order to prevent hard or soft faults, select a current such that the maximum voltage drop across the sensor or sense resistor is nominally 1.0V. The LTC2983 has no special requirements related to the ratio between the voltage drop across the sense resistor and the sensor. Consequently, it is possible to have a sense resistor several orders of magnitude smaller than the maximum sensor value. For optimal performance over the full thermistor temperature range, auto ranged current can be selected. In this case, the LTC2983 conversion is performed in three cycles (instead of the standard two cycles) (see Table 64). The first cycle determines the optimal excitation current for the sensor resistance value and RSENSE value. The following two cycles use that current to measure the thermistor temperature. (3) Sensor Configuration The sensor configuration field is used to define various thermistor properties. Configuration bit B21 is set high for single-ended (measurement relative to COM) and low for differential (see Table 52). The next sensor configuration bits (B19 and B20) determine the excitation current mode. These bits are used to enable RSENSE sharing, where one sense resistor is used for multiple thermistors. In this case, the thermistor ground connection is internal and each thermistor points to the same RSENSE channel. Bits B19 and B20 are also used to enable excitation current rotation to automatically remove parasitic thermocouple effects. Parasitic thermocouple effects may arise from the physical connection between the thermistor and the measurement instrument. This mode is available for differential thermistor configurations using internal current source excitation. Table 52. Sensor Configuration Data (3) SENSOR CONFIGURATION SGL EXCITATION MODE B21 B20 B19 0 0 0 SINGLE-ENDED/ DIFFERENTIAL Differential Table 53. Excitation Current for Thermistors (4) EXCITATION CURRENT B18 B17 B16 B15 CURRENT 0 0 0 0 Reserved 0 0 0 1 250nA 0 0 1 0 500nA 0 0 1 1 1µA 0 1 0 0 5μA 0 1 0 1 10μA 0 1 1 0 25μA 0 1 1 1 50μA 1 0 0 0 100µA 1 0 0 1 250µA SHARE RSENSE ROTATE No No 1 0 1 0 500µA 0 1 1 1mA 0 0 1 Differential Yes Yes 1 0 1 0 Differential Yes No 1 1 0 0 Auto Range* 0 1 1 Reserved 1 1 0 1 Invalid No 1 1 1 0 Invalid 1 1 1 1 Reserved 1 0 0 1 0 1 Single-Ended No Reserved 1 1 0 Reserved *Auto Range not allowed for custom sensors 1 1 1 Reserved (5) Steinhart-Hart Address/Custom Table Address See Custom Thermistors section near the end of this data sheet for more information. 44 2983fc For more information www.linear.com/LTC2983 LTC2983 APPLICATIONS INFORMATION Fault Reporting – Thermistor Each sensor type has unique fault reporting mechanism indicated in the upper byte of the data output word. Table 54 shows faults reported during the measurement of thermistors. Bit D31 indicates the thermistor or RSENSE is open, shorted, or not plugged in. This is a hard fault and –999°C is reported. Bit D30 indicates a bad ADC reading. This could be a result of either a broken (open) sensor or an excessive noise event (ESD or static discharge into the sensor path). This is a hard error and –999°C is output. In the case of an excessive noise event, the device should recover and the following conversions will be valid if the noise event was a random infrequent event. Bits D29 and D28 are not used for thermistors. Bits D27 and D26 indicate the reading is over or under temperature limits (see Table 55). The calculated temperature is reported, but the accuracy may be compromised. Bit D25 indicates the absolute voltage measured by the ADC is beyond its normal operating range. If a thermistor is used as the cold junction element, any hard or soft error is flagged in the thermocouple result. Table 54. Thermistor Fault Reporting BIT FAULT D31 Sensor Hard Fault ERROR TYPE Hard DESCRIPTION Open or Short Thermistor or RSENSE OUTPUT RESULT –999°C D30 Hard ADC-Out-of-Range Hard Bad ADC Reading (Could Be Large External Noise Event) D29 Not Used for Thermistors N/A Always 0 Valid Reading –999°C D28 Not Used for Thermistors N/A Always 0 Valid Reading D27 Sensor Over Range* Soft T > High Temp Limit Suspect Reading D26 Sensor Under Range* Soft T < Low Temp Limit Suspect Reading D25 ADC Out-of-Range Soft ADC Absolute Input Voltage Is Beyond ±1.125 • VREF/2 Suspect Reading D24 Valid N/A Result Valid (Should Be 1) Discard Results if 0 Valid Reading *Do not apply to custom Steinhart-Hart sensor type. Custom table thermistor over/under range is determined by the resistor table values, see custom thermistor table example for details. 2983fc For more information www.linear.com/LTC2983 45 LTC2983 APPLICATIONS INFORMATION Table 55. Thermistor Temperature/Resistance Range THERMISTOR TYPE MIN (Ω) MAX (Ω) LOW Temp Limit (°C) HIGH Temp Limit (°C) Thermistor 44004/44033 2.252kΩ at 25°C 41.9 75.79k –40 150 Thermistor 44005/44030 3kΩ at 25°C 55.6 101.0k –40 150 Thermistor 44007/44034 5kΩ at 25°C 92.7 168.3k –40 150 Thermistor 44006/44031 10kΩ at 25°C 237.0 239.8k –40 150 Thermistor 44008/44032 30kΩ at 25°C 550.2 884.6k –40 150 Thermistor YSI 400 2.252kΩ at 25°C 6.4 1.66M –80 250 Spectrum 1003K 1kΩ at 25°C 51.1 39.51k –50 125 Thermistor Custom Steinhart-Hart N/A N/A N/A N/A Second Table Entry Last Table Entry Thermistor Custom Table Example: Single-Ended Thermistor The simplest thermistor configuration is the single-ended configuration. Thermistors using this configuration share a common ground (COM) between all sensors and are each tied to a unique sense resistor (RSENSE sharing is not allowed for single-ended thermistors). Single-ended thermistors follow the convention shown in Figure 22. Terminal 1 ties to ground (COM) and terminal 2 ties to CHTHERM and the sense resistor. Channel assignment data (see Table 50) is mapped to memory locations corresponding to CHTHERM. 2 1 CHTHERM CHRSENSE-1 EXCITATION CURRENT FLOW RSENSE CHRSENSE CHANNEL = CH RSENSE (2≤ RSENSE ≤ 20) ASSIGNMENT 2983 F23 Figure 23. Sense Resistor Channel Assignment Convention 2ND TERMINAL TIES TO SENSE RESISTOR (CHRSENSE) EXCITATION CURRENT FLOW Sense resistor channel assignments follow the general convention shown in Figure 23. The sense resistor is tied between CHRSENSE and CHRSENSE-1, where CHRSENSE is tied to the 2nd terminal of the thermistor. Channel assignment data (see Table 33) is mapped into the memory location corresponding to CHRSENSE. CHANNEL = CH THERM (1 ≤ THERM ≤ 20) ASSIGNMENT COM 2983 F22 Figure 22. Single-Ended Thermistor Channel Assignment Convention 46 2983fc For more information www.linear.com/LTC2983 LTC2983 APPLICATIONS INFORMATION Figure 24 shows a typical temperature measurement system using a single-ended thermistor. In this example a 10kΩ (44031 type) thermistor is tied to a 10.1kΩ sense resistor. The thermistor is assigned channel CH5 (memory locations 0x210 to 0x213) and the sense resistor to CH4 (memory locations 0x20C to 0x20F). Channel assignment data are shown in Tables 56 and 57. A conversion is initiated on CH5 by writing 10000101 into memory location 0x000. Once the conversion is complete, the INTERRUPT pin goes HIGH and memory location 0x000 becomes 01000101. The resulting temperature in °C can be read from memory locations 0x020 to 0x023 (corresponding to CH5). CH3 100pF RSENSE 10.1k SENSE RESISTOR ASSIGNED TO CH4 (CHSENSE=4) CHANNEL ASSIGNMENT MEMORY LOCATIONS 0x20C TO 0x20F CH4 100pF 2 THERMISTOR ASSIGNED TO CH5 (CHTHERM=5) CHANNEL ASSIGNMENT MEMORY LOCATIONS 0x210 TO 0x213 RESULT MEMORY LOCATIONS 0x020 TO 0x023 CH5 100pF TYPE 44031 1 COM 2983 F24 Figure 24. Single-Ended Thermistor Example Table 56. Channel Assignment Data for Single-Ended Thermistor (44006/44031 10kΩ at 25°C Type Thermistor, Single-Ended Configuration, RSENSE on CH4, 1µA Excitation Current) CONFIGURATION DESCRIPTION # BITS FIELD (1) Thermistor Type BINARY DATA MEMORY ADDRESS 0x210 44006/44031 10kΩ at 25°C 5 10110 1 0 1 1 0 CH4 5 00100 (3) Sensor Configuration Single-Ended 3 100 (4) Excitation Current 1µA 4 0011 Set These Bits to 0 3 000 Not Custom 12 000000000000 (2) Sense Resistor Channel Pointer Not Used (5) Custom RTD Data Pointer MEMORY ADDRESS 0x211 MEMORY ADDRESS 0x212 MEMORY ADDRESS 0x213 0 0 1 0 0 1 0 0 0 0 1 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 Table 57. Channel Assignment Data for Sense Resistor (Value = 10.1kΩ) CONFIGURATION DESCRIPTION # BITS FIELD (1) Sensor Type Sense Resistor 5 (2) Sense Resistor Value 10.1kΩ 27 BINARY DATA MEMORY ADDRESS 0x20C MEMORY ADDRESS 0x20D MEMORY ADDRESS 0x20E MEMORY ADDRESS 0x20F 11101 1 1 1 0 1 000100111011101000000000000 0 0 0 1 0 0 1 1 1 0 1 1 1 0 1 0 0 0 0 0 0 0 0 0 0 00 2983fc For more information www.linear.com/LTC2983 47 LTC2983 APPLICATIONS INFORMATION Example: Differential Thermistor The differential thermistor configuration allows separate ground sensing for each sensor. In this standard differential configuration, one sense resistor is used for each thermistor. Differential thermistors follow the convention shown in Figure 25. Terminal 1 ties to CHTHERM and is shorted to ground and terminal 2 ties CHTHERM-1 to and the sense resistor. Channel assignment data (see Table 50) is mapped to memory locations corresponding to CHTHERM. Sense resistor channel assignments follow the general convention shown in Figure 26. The sense resistor is tied between CHRSENSE and CHRSENSE-1, where CHRSENSE is tied to the 2nd terminal of the thermistor. Channel assignment data (see Table 33) is mapped into a memory location corresponding to CHRSENSE. CHRSENSE-1 EXCITATION CURRENT FLOW RSENSE CHRSENSE CHANNEL = CH RSENSE (2 ≤ RSENSE ≤ 20) ASSIGNMENT 2983 F26 2ND TERMINAL TIES TO SENSE RESISTOR EXCITATION CURRENT FLOW 2 CHTHERM–1 1 CHTHERM Figure 26. Sense Resistor Channel Assignment Convention CHANNEL = CH THERM (2 ≤ THERM ≤ 20) ASSIGNMENT 1ST TERMINAL TIES TO GND 2983 F25 Figure 25. Differential Thermistor Channel Assignment Convention 48 2983fc For more information www.linear.com/LTC2983 LTC2983 APPLICATIONS INFORMATION Figure 27 shows a typical temperature measurement system using a differential thermistor. In this example a 30kΩ (44032 type) thermistor is tied to a 9.99kΩ sense resistor. The thermistor is assigned channel CH13 (memory locations 0x230 to 0x233) and the sense resistor to CH11 (memory locations 0x228 to 0x22B). Channel assignment data is shown in Tables 58 and 59). A conversion is initiated on CH13 by writing 10001101 into memory location 0x000. Once the conversion is complete, the INTERRUPT pin goes HIGH and memory location 0x000 becomes 01001101. The resulting temperature in °C can be read from memory locations 0x040 to 0x043 (Corresponding to CH13). CH10 RSENSE 9.99k 100pF SENSE RESISTOR ASSIGNED TO CH11 (CHSENSE=11) CHANNEL ASSIGNMENT MEMORY LOCATIONS 0x228 TO 0x22B CH11 100pF 2 CH12 100pF TYPE 44032 THERMISTOR ASSIGNED TO CH5 (CHTHERM=13) CHANNEL ASSIGNMENT MEMORY LOCATIONS 0x230 TO 0x233 RESULT MEMORY LOCATIONS 0x040 TO 0x043 CH13 1 2983 F27 Figure 27. Differential Thermistor Example Table 58. Channel Assignment Data for Differential Thermistor (44008/44032 30kΩ at 25°C Type Thermistor, Differential Configuration, RSENSE on CH11, Auto Range Excitation) CONFIGURATION DESCRIPTION # BITS FIELD (1) Thermistor Type BINARY DATA MEMORY ADDRESS 0x230 44008/44032 30kΩ at 25°C 5 10111 1 0 1 1 1 CH11 5 01011 (3) Sensor Configuration Differential, No Share, No Rotate 3 000 (4) Excitation Current Auto Range 4 1100 Set These Bits to 0 2 000 Not Custom 12 000000000000 (2) Sense Resistor Channel Pointer Not Used (5) Custom RTD Data Pointer MEMORY ADDRESS 0x231 MEMORY ADDRESS 0x232 MEMORY ADDRESS 0x233 0 1 0 1 1 0 0 0 1 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 Table 59. Channel Assignment Data for Sense Resistor (Value = 9.99kΩ) CONFIGURATION DESCRIPTION # BITS FIELD (1) Sensor Type Sense Resistor 5 (2) Sense Resistor Value 9.99kΩ 27 BINARY DATA MEMORY ADDRESS 0x228 MEMORY ADDRESS 0x229 MEMORY ADDRESS 0x22A MEMORY ADDRESS 0x22B 11101 1 1 1 0 1 000100111000001100000000000 0 0 0 1 0 0 1 1 1 0 0 0 0 0 1 1 0 0 0 0 0 0 0 0 0 0 0 2983fc For more information www.linear.com/LTC2983 49 LTC2983 APPLICATIONS INFORMATION Example: Shared/Rotated Differential Thermistor The differential thermistor configuration allows separate internal ground sensing for each sensor. In this configuration, one sense resistor can be used for multiple thermistors. Differential thermistors follow the convention shown in Figure 28. Terminal 1 ties to CHTHERM and terminal 2 ties to CHTHERM-1 and the sense resistor. Channel assignment data (see Table 50) is mapped to memory locations corresponding to CHTHERM. Sense resistor channel assignments follow the general convention shown in Figure 29. The sense resistor is tied between CHRSENSE and CHRSENSE-1, where CHSENSE is tied to the 2nd terminal of the thermistor. Channel assignment data (see Table 33) is mapped into a memory location corresponding to CHTHERM. Figure 30 shows a typical temperature measurement system using a shared sense resistor and one rotated/ one non-rotated differential thermistors. In this example 2ND TERMINAL TIES TO SENSE RESISTOR 2 EXCITATION CURRENT FLOW 1 CHRSENSE-1 EXCITATION CURRENT FLOW CHTHERM–1 CHTHERM RSENSE CHRSENSE CHANNEL = CH RSENSE (2 ≤ RSENSE ≤ 20) ASSIGNMENT CHANNEL = CH THERM (2 ≤ THERM ≤ 20) ASSIGNMENT 2983 F28 2983 F29 Figure 29. Sense Resistor Channel Assignment Convention for Thermistors Figure 28. Thermistor with Shared RSENSE Channel Assignment Convention 50 2983fc For more information www.linear.com/LTC2983 LTC2983 APPLICATIONS INFORMATION a 30kΩ (44032 Type) thermistor is tied to a 10.0kΩ sense resistor and configured as rotated/shared. The second thermistor a 2.25kΩ (44004 Type) is configured as a non-rotated/shared. Channel assignment data are shown in Tables 60 to 62. A conversion is initiated on CH18 by writing 10010010 into memory location 0x000. Once the conversion is complete, the INTERRUPT pin goes HIGH and memory location 0x000 becomes 01010010. The resulting temperature in °C can be read from memory locations 0x054 to 0x057 (corresponding to CH16). A conversion can be initiated and read from CH20 in a similar fashion. CH15 RSENSE 10k SENSE RESISTOR ASSIGNED TO CH16 (CHSENSE=16) CHANNEL ASSIGNMENT MEMORY LOCATIONS 0x23C TO 0x23F 100pF CH16 100pF 2 CH17 THERMISTOR #1 ASSIGNED TO CH18 (CHTHERM=18) CHANNEL ASSIGNMENT MEMORY LOCATIONS 0x244 TO 0x247 RESULT MEMORY LOCATIONS 0x054 TO 0x057 100pF TYPE 44032 1 CH18 100pF 2 CH19 100pF TYPE 44033 1 THERMISTOR #2 ASSIGNED TO CH20 (CHTHERM=20) CHANNEL ASSIGNMENT MEMORY LOCATIONS 0x24C TO 0x24F RESULT MEMORY LOCATIONS 0x05C TO 0x05F CH20 100pF 2983 F30 Figure 30. Rotated and Shared Thermistor Example Table 60. Channel Assignment Data Differential Thermistor (44008/44032 30kΩ at 25°C Type Thermistor, Differential Configuration with Sharing and Rotation, RSENSE on CH16, 250nA Excitation Current) CONFIGURATION DESCRIPTION # BITS FIELD (1) Thermistor Type BINARY DATA MEMORY ADDRESS 0x244 44008/44032 30kΩ at 25°C 5 10111 1 0 1 1 1 CH16 5 10000 (3) Sensor Configuration Differential, Rotate and Shared 3 001 (4) Excitation Current 250nA Excitation Current 4 0001 Set These Bits to 0 3 000 Not Custom 12 000000000000 (2) Sense Resistor Channel Pointer Not Used (5) Custom RTD Data Pointer MEMORY ADDRESS 0x245 MEMORY ADDRESS 0x246 MEMORY ADDRESS 0x247 1 0 0 0 0 0 0 1 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 2983fc For more information www.linear.com/LTC2983 51 LTC2983 APPLICATIONS INFORMATION Table 61. Channel Assignment Data Differential Thermistor (44004/44033 2.252kΩ at 25°C Type Thermistor, Differential Configuration with Sharing and No Rotation, RSENSE on CH16, 10µA Excitation Current) Configuration Field (1) Thermistor Type Description # Bits Binary Data MEMORY ADDRESS 0x24C 44004/44033 2.252kΩ at 25°C 5 10011 1 0 0 1 1 CH16 5 10000 (3) Sensor Configuration Differential, No Rotate and Shared 3 010 (4) Excitation Current 10µA Excitation Current 4 0101 Not Used Set These Bits to 0 3 000 Not Custom 12 000000000000 (2) Sense Resistor Channel Pointer (5) Custom RTD Data Pointer MEMORY ADDRESS 0x24D MEMORY ADDRESS 0x24E MEMORY ADDRESS 0x24F 1 0 0 0 0 0 1 0 0 1 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 Table 62. Channel Assignment Data for Sense Resistor (Value = 10.0kΩ) Configuration Field Description # Bits (1) Sensor Type Sense Resistor 5 (2) Sense Resistor Value 27 52 10.0kΩ Binary Data MEMORY ADDRESS 0x23C MEMORY ADDRESS 0x23D MEMORY ADDRESS 0x23E MEMORY ADDRESS 0x23F 11101 1 1 1 0 1 000100111000100000000000000 0 0 0 1 0 0 1 1 1 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 2983fc For more information www.linear.com/LTC2983 LTC2983 APPLICATIONS INFORMATION Typical Application Thermocouple Measurements The LTC2983 includes 20 fully configurable analog input channels. Each input channel can be configured to accept any sensor type. Figure 31 shows a typical application digitizing multiple thermocouples. Each thermocouple requires a cold junction sensor and each cold junction sensor can be shared amongst multiple thermocouples. For example, the thermocouple tied to CH1 can use the diode tied to CH2 as a cold junction sensor. However, any thermocouple (CH1, CH3, CH5, CH6, CH9, CH10, or CH16) can use any diode (CH2, CH4, or CH7), RTD (CH13, CH14), or Thermistor (CH19, CH20) as its cold junction compensation. The LTC2983 simultaneously measures both the thermocouple and cold junction sensor and outputs the results in °C or °F. 2.85V TO 5.25V 16 CH1 VDD CH2 Q1 2, 4, 6, 8, 45 0.1µF 17 Q2 18 19 20 21 22 CH3 CH4 Q3 VREFOUT VREFP 48 47 46 10µF 13 14 1µF CH5 CH6 CH7 10µF VREF_BYP 11 1µF LDO 43 10µF 23 24 25 CH8 CH9 CH10 RESET CS 26 CH11 RSENSE 27 28 4-WIRE RTD 29 30 31 32 RSENSE 33 34 35 36 CH12 CH13 CH14 SDI SDO SCK INTERRUPT CH15 CH16 GND 42 (OPTIONAL, DRIVE LOW TO RESET) 41 40 39 SPI INTERFACE 38 37 1, 3, 5, 7, 9, 12, 15, 44 CH17 CH18 CH19 CH20 COM 2983 F31 Figure 31. Typical Thermocouple Application 2983fc For more information www.linear.com/LTC2983 53 LTC2983 APPLICATIONS INFORMATION Typical Application RTD and Thermistor Measurements The LTC2983 includes 20 fully configurable analog input channels. Each input channel can be configured to accept any sensor type. Figure 32 shows a typical application digitizing multiple RTDs and thermistors. Each RTD/ thermistor requires a sense resistor which can be shared with multiple sensors. RTDs can be configured as 2, 3, or 4-wire topologies. For example, a single sense resistor (CH1, CH2) is shared between a 4-wire RTD (CH4, CH3), a 2-wire RTD (CH7, CH6), two 3-wire RTDs (CH9, CH8 and CH11, CH10) and a thermistor (CH13, CH12). This can be mixed with diode sensors (CH15) and thermocouples (CH14). Sense resistors (CH17, CH16) can also be dedicated to specific sensors, in this case a 4-wire RTD (CH19, CH18). Current is applied through both the sense resistor and RTD/Thermistor, the resulting voltages are simultaneously measured and the results are output in °C or °F. 2.85V TO 5.25V 16 RSENSE CH1 VDD CH2 Q1 0.1µF 17 Q2 18 4-WIRE RTD 19 20 21 2-WIRE RTD 22 23 3-WIRE RTD 24 25 3-WIRE RTD CH3 CH4 Q3 VREFOUT VREFP CH6 CH7 CH9 CH10 CH14 32 33 4-WIRE RTD 34 35 36 10µF 13 14 1µF 1µF LDO 43 10µF RESET SDI SDO SCK INTERRUPT CH15 GND 31 10µF 46 CH8 26 CH11 27 CH12 30 47 VREF_BYP 11 CS 29 48 CH5 28 CH13 RSENSE 2, 4, 6, 8, 45 42 (OPTIONAL, DRIVE LOW TO RESET) 41 40 39 SPI INTERFACE 38 37 1, 3, 5, 7, 9, 12, 15, 44 CH16 CH17 CH18 CH19 CH20 COM 2983 F32 Figure 32. Typical RTD/Thermistor Application 54 2983fc For more information www.linear.com/LTC2983 LTC2983 SUPPLEMENTAL INFORMATION + CHADC SINGLE-ENDED COM – CHADC + DIFFERENTIAL 24-BIT ∆∑ ADC CHANNEL = CHADC (1 ≤ ADC ≤ 20) ASSIGNMENT 24-BIT ∆∑ ADC CHANNEL = CHADC (2 ≤ ADC ≤ 20) ASSIGNMENT – CHADC-1 2983 F33 Figure 33. Direct ADC Channel Assignment Conventions Direct ADC Measurements ential readings and 0xF400 0000 for single-ended. The positive input channel ties to CHADC for both single-ended and differential modes. For single-ended measurements the ADC negative input is COM while for differential measurements it is CHADC-1. For single ended measurements, COM can be driven with any voltage above GND – 50mV and below VDD – 0.3V. In addition to measuring temperature sensors, the LTC2983 can perform direct voltage measurements. Any channel can be configured to perform direct single-ended or differential measurements. Direct ADC channel assignments follow the general convention shown in Figure 33. The 32-bit channel assignment word is programmed into a memory location corresponding to the input channel. The channel assignment word is 0xF000 0000 for differ- The direct ADC results are available in memory at a location corresponding to the conversion channel. Table 63. Direct ADC Output Format START ADDRESS D31 D30 D29 D28 D27 START ADDRESS + 1 D26 D25 D24 Fault Data LSB ± 2V 1V 0.5V 0.25V ... Integer >VREF 1 1 0 0 1 0 1 START ADDRESS + 3 (END ADDRESS) D23 D22 D21 D20 D19 D18 D17 D16 D15 D14 D13 D12 D11 D10 D9 D8 D7 D6 D5 D4 D3 D2 D1 D0 SIGN MSB Sensor Range NA NA Soft Soft Soft Valid Above Below Range Always Hard Hard 1 Fault Fault Volts START ADDRESS + 2 Fraction CLAMPED to Factory Programmed Value of VREF 1.75 • VREF/2 1 1 0 0 1 0 1 1 0 1 0 0 0 1 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1.125 • VREF/2 0 0 0 0 1 0 1 1 0 0 1 0 1 1 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 VREF/2 0 0 0 0 0 0 0 1 0 0 1 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 VREF/222 0 0 0 0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 0 0 0 0 0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 –VREF/222 0 0 0 0 0 0 0 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 –VREF/2 0 0 0 0 0 0 0 1 1 1 0 1 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 –1.125 • VREF 0 0 0 0 0 1 1 1 1 1 0 1 0 0 1 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 –1.75 • VREF 1 1 0 0 0 1 1 1 1 0 1 1 1 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 < –VREF 1 1 0 0 0 1 1 1 CLAMPED to Factory Programmed Value of –VREF 2983fc For more information www.linear.com/LTC2983 55 LTC2983 SUPPLEMENTAL INFORMATION VREF/2 exceed the usable range of the LTC2983; these result in a hard fault and should be discarded. Figures 34 to 36 show typical integral nonlinearity variation at various supply voltages and temperatures for a differential input voltage (±VREF/2) and VREF/2 common mode input voltage. 20 20 15 15 10 10 INL ERROR (ppm) INL ERROR (ppm) The data is represented as a 32-bit word (see Table 63) where the eight most significant bits are fault bits and the bottom 24 are the ADC reading in volts. For direct ADC readings hard fault errors do not clamp the digital output. Readings beyond ±1.125 • VREF/2 exceed the normal accuracy range of the LTC2983 and flag a soft error; these results should be discarded. Readings beyond ±1.75 • 5 0 –5 –10 –15 –20 –1.5 5 0 –5 –10 90°C 25°C –45°C –1 –0.5 0 0.5 1 DIFFERENTIAL INPUT VOLTAGE (V) 90°C 25°C –45°C –15 –20 –1.5 1.5 –1 –0.5 0 0.5 1 DIFFERENTIAL INPUT VOLTAGE (V) 2983 F34 1.5 2983 F35 Figure 34. Integral Nonlinearity as a Function of Temperature at VDD = 5.25V Figure 35. Integral Nonlinearity as a Function of Temperature at VDD = 3.3V 20 15 INL ERROR (ppm) 10 5 0 –5 –10 –15 –20 –1.5 90°C 25°C –45°C –1 –0.5 0 0.5 1 DIFFERENTIAL INPUT VOLTAGE (V) 1.5 2983 F36 Figure 36. Integral Nonlinearity as a Function of Temperature at VDD = 2.85V 56 2983fc For more information www.linear.com/LTC2983 LTC2983 SUPPLEMENTAL INFORMATION Fault Protection and Anti-Aliasing The LTC2983 analog input channels draw a maximum of 1nA DC. As a result, it is possible to add anti-aliasing and fault protection circuitry directly to the input of the LTC2983. The most common input circuitry is a low pass filter with 1k to 10k resistance (limited by excitation current for RTDs and thermistors) and a capacitor with 100pF-0.1µf capacitance. This circuit can be placed directly between the thermocouples and 4-wire RTDs and the LTC2983. In the case of 3-wire RTDs, mismatch errors between the protection resistors can degrade the performance. Thermistors requiring input projection should be tied to the LTC2983 through a Kelvin type connection in order to avoid errors due to the fault protection resistors. 2- and 3-Cycle Conversion Modes The LTC2983 performs multiple internal conversions in order to determine the sensor temperature. Normally, two internal conversion cycles are required for each temperature result providing a maximum output time of 167.2ms. The LTC2983 uses these two cycles to automatically remove offset/offset drift errors, reduce 1/f noise, autocalibrate matched internal current sources, and provide simultaneous 50/60Hz noise rejection. In addition to performing two conversion cycles per result, the LTC2983 also offers several unique features by utilizing a 3rd conversion cycle. In this case, the maximum output time is 251ms and all the benefits of the 2-cycle modes are present (see Table 64). One feature utilizing the three conversion cycle mode is the internal open circuit detect mode. Typically, thermocouple open circuit detection is performed by adding a high resistance pull-up between the thermocouple and VDD. This method can be used with the LTC2983 while operating in the two conversion cycle mode (OC=0). This external pull-up can interact with the input protection circuitry and lead to temperature measurement errors and increased noise. These problems are eliminated by selecting the internal open circuit detection mode (OC=1). In this case, a current is pulsed for 8ms and allowed to settle during one conversion cycle. This is followed by the normal two conversion cycle measurement of the thermocouple. If the thermocouple is broken, the current pulse will result in an open circuit fault. A second feature taking advantage of the 3rd conversion cycle is thermistor excitation current auto ranging. Since a thermistor’s resistance varies many orders of magnitude, the performance in the low resistance regions are compromised by the small currents required by the high resistance regions of operation. The auto ranging mode applies a test current during the first conversion cycle in order to determine the optimum current for the resistance state of the thermistor. It then uses that current to perform the thermistor measurement using the normal 2-cycle measurement. If a 3-cycle thermistor measurement is used as the cold junction sensor for a 2-cycle thermocouple measurement, the thermocouple conversion result is ready after three cycles. A third feature requiring a 3rd conversion cycle is the three current diode measurement. In this mode, three ratioed currents are applied to the external diode in order to cancel parasitic lead resistance effects. This is useful in applications where the diode is remotely located and significant, unknown parasitic lead resistance requires cancellation. If a 3-cycle diode or thermistor measurement is used as the cold junction sensor for a 2-cycle thermocouple measurement, the thermocouple conversion result is ready after three cycles. Table 64. 2- and 3-Cycles Conversion Modes TYPE OF SENSOR CONFIGURATION NUMBER OF MAXIMUM OUTPUT CONVERSION TIME CYCLES Thermocouple OC = 0 2 167.2ms All 2 167.2ms Thermistor Non-Autorange Current 2 167.2ms Diode RTD Two Readings 2 167.2ms Thermocouple OC = 1 3 251ms Thermocouple OC = 0, 3-Cycle Cold Junction 3 251ms Autorange Current 3 251ms Three Readings 3 251ms Thermistor Diode 2983fc For more information www.linear.com/LTC2983 57 LTC2983 SUPPLEMENTAL INFORMATION Entering/Exiting Sleep Mode Running Conversions Consecutively on Multiple Channels Generally, during the Initiate Conversion state, a conversion measurement is started on a single input channel determined by the channel number (bits B[4:0] = 00001 to 10100) written into memory location 0x000. Multiple consecutive conversions can be initiated by writing bits B[4:0]=00000 into memory location 0. Conversions will be initiated on each channel selected in the mask register (see Table 65). For example, using the mask data shown in Table 66, after 1000000 is written into memory location 0, conversions are initiated consecutively on CH20, CH19, CH16, and CH1. Once the conversions begin, the INTERRUPT pin goes LOW and remains LOW until all conversions are complete. If the mask register is set for a channel that has no assignment data, that conversion step is skipped. All the results are stored in the conversion result memory locations and can be read at the conclusion of the measurement cycle. The LTC2983 can be placed into sleep mode by writing 0x97 to memory location 0x000. On the rising edge of CS following the memory write (see Figure 2) the device enters the low power sleep state. It remains in this state until CS is brought low or RESET is asserted. Once one of these two signals is asserted, the LTC2983 begins its start-up cycle as described in State 1: Start-Up section of this data sheet. MUX Configuration Delay The LTC2983 performs 2 or 3 internal conversion cycles per temperature result. Each conversion cycle is performed with different excitation and input multiplexer configurations. Prior to each conversion, these excitation circuits and input switch configurations are changed and an internal 1ms (typical) delay ensures settling prior to the conversion cycle in most cases. Table 65. Multiple Conversion Mask Register MEMORY LOCATION B7 0x0F4 B6 B5 B4 B3 B2 B1 B0 CH20 CH19 CH18 CH17 Reserved 0x0F5 0x0F6 CH16 CH15 CH14 CH13 CH12 CH11 CH10 CH9 0x0F7 CH8 CH7 CH6 CH5 CH4 CH3 CH2 CH1 B5 B4 B3 B2 B1 B0 Table 66. Example Mask Register Select CH20, CH19, CH16, and CH1 MEMORY LOCATION B7 0x0F4 B6 Reserved 0x0F5 58 1 1 0 0 0x0F6 1 0 0 0 0 0 0 0 0x0F7 0 0 0 0 0 0 0 1 2983fc For more information www.linear.com/LTC2983 LTC2983 SUPPLEMENTAL INFORMATION The default temperature units reported by the LTC2983 are °C. The reported temperature can also be output in °F by setting bit 3 of memory location 0x0F0 to 1. All other global configuration bits should be set to 0. MEMORY LOCATION 0x0F0 0 0 0 0 0 } If excessive RC time constants are present in external sensor circuits (large bypass capacitors used for thermistors or RTDs) it is possible to increase the settling time between current source excitation and MUX switching. The extra delay is determined by the value written into the MUX configuration delay register (memory location 0x0FF). The value written into this memory location is multiplied by 100µs; therefore the maximum extra MUX delay is 25.5ms (i.e. 0x0FF = 255 • 100µs). 0 = °C 1 = °F 00 01 10 11 50/60Hz REJECTION 60Hz REJECTION 50Hz REJECTION RESERVED 2983 F37 Global Configuration Register Figure 37. Global Configuration Register The LTC2983 includes a global configuration register (memory location 0x0F0, see Figure 37). This register is used to set the notch frequency of the digital filter and temperature results format (°C or °F). The default setting is simultaneous 50/60Hz rejection (75dB rejection with 1ms MUX delay). If higher 60Hz rejection is required (120dB rejection), write 0x01 into memory location 0x0F0; if higher 50Hz rejection is required (120dB rejection) write 0x02 into memory location 0x0F0. Reference Considerations The mechanical stress of soldering the LTC2983 to a PC board can cause the output voltage reference to shift and temperature coefficient to change. These two changes are not correlated. For example, the voltage may shift but the temperature coefficient may not. To reduce the effects of stress-related shifts, mount the reference near the short edge of the PC board or in a corner. CUSTOM THERMOCOUPLES In addition to digitizing standard thermocouples, the LTC2983 can also digitize user-programmable, custom thermocouples (thermocouple type=0b01001, see Table 12). Custom sensor data (minimum of three, maximum of 64 pairs) reside sequentially in memory and are arranged in blocks of six bytes of monotonically increasing tabular data as mV vs temperature (see Table 67). Table 67. Custom Thermocouple Tabular Data Format ADDRESS BYTE 0 BYTE 1 BYTE 2 BYTE 3 BYTE 4 BYTE 5 0x250 + 6* Start Address Custom Thermocouple Example In this example, a simplified thermocouple curve is implemented (see Figure 38). Points P1 to P9 represent the normal operating range of the custom thermocouple. Voltage readings above point P9 result in a soft fault and the reported temperature is a linear extrapolation using TEMPERATURE (K) VOLTAGE < p1 SOFT FAULT CONDITION VOLTAGE > p9 SOFT FAULT CONDITION (0mV, 273.15K) Table Entry #1 (mV) Table Entry #1 (Kelvin) 0x250 + 6* Start Address + 6 Table Entry #2 (mV) Table Entry #2 (Kelvin) p7 • • • • • • • • p5 NOTE: P0 SHOULD BE THE EXTRAPOLATION POINT TO 0K p4 p1 p0 Max Address = 0x3CA Table Entry #64 (mV) Table Entry #64 (Kelvin) p9 p6 0x250 + 6* Start Address + 12 Table Entry #3 (mV) Table Entry #3 (Kelvin) • p8 p2 p3 (0mV, 0K) VOLTAGE (mV) 2983 F38 Figure 38. Custom Thermocouple Example (mV vs Kelvin) 2983fc For more information www.linear.com/LTC2983 59 LTC2983 CUSTOM THERMOCOUPLES a slope determined by points P8 and P9 (the final two table entries). Voltage readings below point P1 are also reported as soft faults. The temperature reported is the extrapolation between point P1 and P0, where P0 is typically the sensor output voltage at 0 Kelvin. If P0 is above 0 Kelvin, then all sensor output voltages below P0 (in mV) will report 0 Kelvin. In order to program the LTC2983 with the custom thermocouple table, both the mV data and the Kelvin data are converted to 24-bit binary values (represented as two 3-byte table entries). Since most thermocouples generate negative output voltages, the mV values input to the LTC2983 are 2’s compliment. The sensor output voltage (units=mV), follows the convention shown in Table 69, where the first bit is the sign, the next nine are the integer part and the remaining 14 bits are the fractional part. Table 68. Thermocouple Example mV vs Kelvin (K) Data Memory Map POINT SENSOR OUTPUT TEMPERATURE START VOLTAGE (mV) KELVIN ADDRESS P0 –50.22 P1 –30.2 P2 –5.3 0 STOP ADDRESS 0x250 0x255 99.1 0x256 0x25B 135.4 0x25C 0x261 BYTE 0 BYTE 1 BYTE 2 BYTE 3 BYTE 4 BYTE 5 P3 0 273.15 0x262 0x267 P4 40.2 361.2 0x268 0x26D mV Data Temperature Data P5 55.3 522.1 0x26E 0x273 (see Table 69) (see Table 70) P6 88.3 720.3 0x274 0x279 P7 132.2 811.2 0x27A 0x27F P8 188.7 922.5 0x280 0x285 P9 460.4 1000 0x286 0x28B Table 69. Example Thermocouple Output Voltage Values (mV) BYTE 0 BYTE 1 BYTE 2 B23 B22 B21 B20 B19 B18 B17 B16 B15 B14 B13 B12 B11 B10 B9 mV Sign B8 B7 B6 B5 B4 B3 B2 B1 B0 2–7 2–8 2–9 2–10 2–11 2–12 2–13 2–14 28 27 26 25 24 23 22 21 20 2–1 2–2 2–3 2–4 2–5 2–6 –50.22 1 1 1 1 0 0 1 1 0 1 1 1 0 0 0 1 1 1 1 0 1 1 0 0 –30.2 1 1 1 1 1 0 0 0 0 1 1 1 0 0 1 1 0 0 1 1 0 1 0 0 –5.3 1 1 1 1 1 1 1 0 1 0 1 0 1 1 0 0 1 1 0 0 1 1 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 40.2 0 0 0 0 1 0 1 0 0 0 0 0 1 1 0 0 1 1 0 0 1 1 0 0 55.3 0 0 0 0 1 1 0 1 1 1 0 1 0 0 1 1 0 0 1 1 0 0 1 1 88.3 0 0 0 1 0 1 1 0 0 0 0 1 0 0 1 1 0 0 1 1 0 0 1 1 132.2 0 0 1 0 0 0 0 1 0 0 0 0 1 1 0 0 1 1 0 0 1 1 0 0 188.7 0 0 1 0 1 1 1 1 0 0 1 0 1 1 0 0 1 1 0 0 1 1 0 0 460.4 0 1 1 1 0 0 1 1 0 0 0 1 1 0 0 1 1 0 0 1 1 0 0 1 60 2983fc For more information www.linear.com/LTC2983 LTC2983 CUSTOM THERMOCOUPLES channel assignment data shown in Table 71 (refer to Figure 6 for similar format). In this case the custom data begins at memory location 0x250 (starting address is 0). The starting address (offset from 0x250) is entered in the custom thermocouple data pointer field of the channel assignment data. The table data length –1 (9 in this example) is entered into the custom thermocouple data length field of the thermocouple channel assignment word. Refer to Table 68 where the number of six byte entries is 10. In order to simplify the temperature field, temperature values are input in Kelvin as an unsigned value, but the final temperatures reported by the LTC2983 are reported in °C or °F. The sensor temperature (Kelvin), follows the convention shown in Table 70, where the first 14 bits are the integer part and the remaining 10 bits are the fractional part. In this example, a custom thermocouple tied to CH1, with a cold junction sensor on CH2, is programmed with the Table 70. Example Thermocouple Temperature Values BYTE 3 BYTE 4 BYTE 5 B23 B22 B21 B20 B19 B18 B17 B16 B15 B14 B13 B12 B11 B10 B9 B8 B7 B6 B5 B4 B3 B2 B1 B0 213 212 211 210 29 28 27 26 25 24 23 22 21 20 2–1 2–2 2–3 2–4 2–5 2–6 2–7 2–8 2–9 2–10 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 99.1 0 0 0 0 0 0 0 1 1 0 0 0 1 1 0 0 0 1 1 0 0 1 1 0 Temperature 135.4 0 0 0 0 0 0 1 0 0 0 0 1 1 1 0 1 1 0 0 1 1 0 0 1 273.15 0 0 0 0 0 1 0 0 0 1 0 0 0 1 0 0 1 0 0 1 1 0 0 1 361.2 0 0 0 0 0 1 0 1 1 0 1 0 0 1 0 0 1 1 0 0 1 1 0 0 522.1 0 0 0 0 1 0 0 0 0 0 1 0 1 0 0 0 0 1 1 0 0 1 1 0 720.3 0 0 0 0 1 0 1 1 0 1 0 0 0 0 0 1 0 0 1 1 0 0 1 1 811.2 0 0 0 0 1 1 0 0 1 0 1 0 1 1 0 0 1 1 0 0 1 1 0 0 922.5 0 0 0 0 1 1 1 0 0 1 1 0 1 0 1 0 0 0 0 0 0 0 0 0 1000 0 0 0 0 1 1 1 1 1 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 Table 71. Custom Thermocouple Channel Assignment Data CONFIGURATION FIELD DESCRIPTION # BITS BINARY DATA MEMORY ADDRESS 200 (1) Thermocouple Type Type Custom 5 01001 0 1 0 0 1 (2) Cold Junction Channel Pointer CH2 5 00010 (3) Sensor Configuration Single-Ended, 10µA Open Circuit 4 1100 Not Used Set These Bits to 0 6 000000 (4) Custom Thermocouple Data Pointer Start Address = 0 (Start at 0x250) 6 000000 Custom Data Length –1 Thermocouple Data =9 Length-1 (10 Paired Entries) 6 001010 MEMORY ADDRESS 201 MEMORY ADDRESS 202 MEMORY ADDRESS 203 0 0 0 1 0 1 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 0 0 1 2983fc For more information www.linear.com/LTC2983 61 LTC2983 CUSTOM RTDS Table 72. Custom RTD/Thermistor Tabular Data Format ADDRESS BYTE 0 BYTE 1 BYTE 2 BYTE 3 BYTE 4 BYTE 5 0x250 + 6* Start Address Table Entry #1 (Ω) Table Entry #1 (Kelvin) 0x250 + 6* Start Address + 6 Table Entry #2 (Ω) Table Entry #2 (Kelvin) 0x250 + 6* Start Address + 12 Table Entry #3 (Ω) Table Entry #3 (Kelvin) • • • • • • • • • Table Entry #64 (Ω) Table Entry #64 (Kelvin) Max Address = 0x3CA Custom RTD Example In this example, a simplified RTD curve is implemented (see Figure 39). Points P1 to P9 represent the normal operating range of the custom RTD. Resistance readings above point P9 result in a soft fault and the reported temperature is a linear extrapolation using a slope determined by points P8 and P9 (the final two table entries). Resistance readings below point P1 are also reported as soft faults. The temperature reported is the extrapolation between point P1 and P0, where P0 is the sensor output temperature at 0Ω (This point should be 0Ω for proper interpolation below point p1). RESISTANCE < p1 SOFT FAULT CONDITION TEMPERATURE (K) In addition to digitizing standard RTDs, the LTC2983 can also digitize custom RTDs (RTD type=0b10010, see Table 26). Custom sensor data (minimum of three, maximum of 64 pairs) reside sequentially in memory and are arranged in blocks of six bytes of monotonically increasing tabular data Ω vs temperature (see Table 72). RESISTANCE > p9 SOFT FAULT CONDITION p7 p9 p6 p5 NOTE: P0 SHOULD BE THE EXTRAPOLATION POINT TO 0Ω 0 p8 p4 p3 p1 p0 0 p2 RESISTANCE (Ω) 2983 F39 Figure 39. Custom RTD Example (Ω vs Kelvin ) 62 2983fc For more information www.linear.com/LTC2983 LTC2983 CUSTOM RTDS Custom RTD table data is formatted in Ω (sensor output resistance) vs Kelvin (see Table 73). Each table entry pair spans six bytes. The first set of data can begin at any memory location greater than or equal to 0x250 and end at or below 0x3CF. In order to program the LTC2983 with the custom RTD table, both the resistance data and the Kelvin data are converted to 24-bit binary values. The sensor output resistance (units=Ω) follows the convention shown in Table 74, where the first 13 bits are the integer part and the remaining 11 bits are the fractional part. In order to simplify the temperature field, temperature values are input in Kelvin as an unsigned value, but the final temperatures reported by the LTC2983 are reported in °C or °F. The sensor temperature (Kelvin) follows the Table 73. RTD Example Resistance vs Kelvin Data Memory Map POINT SENSOR OUTPUT TEMPERATURE START RESISTANCE (Ω) (K) ADDRESS STOP ADDRESS P0 0 112.3 0x28C 0x291 P1 80 200.56 0x292 0x297 P2 150 273.16 0x298 0x29D P3 257.36 377.25 0x29E 0x2A3 P4 339.22 489.66 0x2A4 0x2A9 P5 388.26 595.22 0x2AA 0x2AF P6 512.99 697.87 0x2B0 0x2B5 P7 662.3 765.14 0x2B6 0x2BB P8 743.5 801.22 0x2BC 0x2C1 P9 2001.89 900.5 0x2C2 0x2C7 BYTE 1 BYTE 2 BYTE 3 BYTE 1 Resistance Data BYTE 2 BYTE 3 Temperature Data Table 74. Example RTD Resistance Values BYTE 1 BYTE 2 BYTE 3 B23 B22 B21 B20 B19 B18 B17 B16 B15 B14 B13 B12 B11 B10 B9 Resistance 212 211 210 29 28 27 26 25 24 23 22 21 20 B5 B4 B3 B2 2–1 2–2 2–3 2–4 2–5 2–6 B8 B7 B6 2–7 2–8 2–9 2–10 2–11 B1 B0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 80 0 0 0 0 0 0 1 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 150 0 0 0 0 0 1 0 0 1 0 1 1 0 0 0 0 0 0 0 0 0 0 0 0 257.36 0 0 0 0 1 0 0 0 0 0 0 0 1 0 1 0 1 1 1 0 0 0 0 1 339.22 0 0 0 0 1 0 1 0 1 0 0 1 1 0 0 1 1 1 0 0 0 0 1 0 388.26 0 0 0 0 1 1 0 0 0 0 1 0 0 0 1 0 0 0 0 1 0 1 0 0 512.99 0 0 0 1 0 0 0 0 0 0 0 0 0 1 1 1 1 1 1 0 1 0 1 1 662.3 0 0 0 1 0 1 0 0 1 0 1 1 0 0 1 0 0 1 1 0 0 1 1 0 743.5 0 0 0 1 0 1 1 1 0 0 1 1 1 1 0 0 0 0 0 0 0 0 0 0 2001.89 0 0 1 1 1 1 1 0 1 0 0 0 1 1 1 1 0 0 0 1 1 1 1 0 2983fc For more information www.linear.com/LTC2983 63 LTC2983 CUSTOM RTDS convention shown in Table 75, where the first 14 bits are the integer part and the remaining 10 bits are the fractional part. at memory location 0x28C (starting address is 10). The starting address (offset from 0x250) is entered in the custom RTD data pointer field of the channel assignment data. The table data length –1 (9 in this case) is entered into the custom RTD data length field of the channel assignment word. Refer to Table 72 where the total number of paired entries is 10. In this example, a custom RTD tied to CH12/13, with a sense resistor on CH10/11, is programmed with the channel assignment data shown in Table 76 (refer to Figure 15 for a similar format). In this case, the custom data begins Table 75. Example RTD Temperature Values BYTE 1 BYTE 2 BYTE 3 B23 B22 B21 B20 B19 B18 B17 B16 B15 B14 B13 B12 B11 B10 B9 B8 B7 B6 B5 B4 B3 B2 B1 B0 213 212 211 210 29 28 27 26 25 24 23 22 21 20 2–1 2–2 2–3 2–4 2–5 2–6 2–7 2–8 2–9 2–10 112.3 0 0 0 0 0 0 0 1 1 1 0 0 0 0 0 1 0 0 1 1 0 0 1 1 200.56 0 0 0 0 0 0 1 1 0 0 1 0 0 0 1 0 0 0 1 1 1 1 0 1 273.16 0 0 0 0 0 0 1 0 0 1 0 0 0 1 0 0 1 0 1 0 0 0 1 1 377.25 0 0 0 0 0 0 1 1 1 1 1 0 0 1 0 1 0 0 0 0 0 0 0 0 489.66 0 0 0 0 0 0 0 1 1 0 1 0 0 1 1 0 1 0 1 0 0 0 1 1 595.22 0 0 0 0 1 0 0 1 0 1 0 0 1 1 0 0 1 1 1 0 0 0 0 1 697.87 0 0 0 0 1 0 1 0 1 1 1 0 0 1 1 1 0 1 1 1 1 0 1 0 Temperature 765.14 0 0 0 0 1 1 0 1 1 1 1 1 0 1 0 0 1 0 0 0 1 1 1 1 801.22 0 0 0 0 1 0 1 0 1 0 0 0 0 1 0 0 1 1 1 0 0 0 0 1 900.5 0 0 0 0 1 1 1 0 0 0 0 1 0 0 1 0 0 0 0 0 0 0 0 0 Table 76. Custom RTD Channel Assignment Data CONFIGURATION FIELD (1) RTD Type DESCRIPTION # BITS BINARY DATA MEMORY ADDRESS 230 Custom 5 10010 1 0 0 1 0 CH11 5 01011 4-Wire, No Rotate, No Share 4 1000 25µA 4 0011 (5) Curve Not Used for Custom 2 00 (6) Custom RTD Data Pointer Start Address = 10 6 001010 6 001001 (2) Sense Resistor Channel Pointer (3) Sensor Configuration (4) Excitation Current (6) Custom RTD Data Data Length –1 Length-1 =9 10 Paired Entries 64 MEMORY ADDRESS 231 MEMORY ADDRESS 232 MEMORY ADDRESS 233 0 1 0 1 1 1 0 0 0 0 0 1 1 0 0 0 0 1 0 1 0 0 0 1 0 0 1 2983fc For more information www.linear.com/LTC2983 LTC2983 CUSTOM THERMISTORS In addition to digitizing standard thermistors, the LTC2983 can also digitize custom thermistors (thermistor type=0b11011, see Table 51). Custom sensor data (minimum of three, maximum of 64 pairs) reside sequentially in memory and are arranged in blocks of six bytes of monotonically increasing tabular data Ω vs temperature (see Table 72). Custom Thermistor Table Example In this example, a simplified thermistor NTC (negative temperature coefficient) curve is implemented (see Figure 40). Points P1 to P9 represent the normal operating range of the custom thermistor. Resistance readings above point In addition to NTC type thermistors, it is also possible to implement PTC (positive temperature coefficient) type thermistors (see Figure 41). In both cases, table entries start at the minimum resistance and end at the maximum resistance value. RESISTANCE > p9 SENSOR OVER-RANGE SOFT FAULT CONDITION TEMPERATURE (K) RESISTANCE < p1 SENSOR UNDER-RANGE SOFT FAULT CONDITION TEMPERATURE (K) P9 result in a soft fault and the reported temperature is a linear extrapolation using a slope determined by points P8 and P9 (the final two table entries). Resistance readings below point P1 are also reported as soft faults. The temperature reported is the extrapolation between point P1 and P0, where P0 is the sensor output temperature at 0Ω (This point must be 0Ω for proper interpolation below point p1). p0 NOTE: P0 SHOULD BE THE EXTRAPOLATION POINT TO 0Ω p9 RESISTANCE < p1 SENSOR UNDER-RANGE SOFT FAULT CONDITION p8 p1 p3 p4 0 0 p7 NOTE: P0 SHOULD BE THE EXTRAPOLATION POINT TO 0Ω p2 p5 p1 p6 p7 p8 p9 0 p0 0 p2 p3 p6 p4 p5 RESISTANCE > p9 SENSOR OVER-RANGE SOFT FAULT CONDITION RESISTANCE (Ω) 2983 F41 RESISTANCE (Ω) 2983 F40 Figure 41. Custom PTC Thermistor Example (Ω vs Kelvin) Figure 40. Custom NTC Thermistor Example (Ω vs Kelvin) 2983fc For more information www.linear.com/LTC2983 65 LTC2983 CUSTOM THERMISTORS Custom thermistor table data is formatted in Ω (sensor output resistance) vs Kelvin (see Table 77). Each table entry pair spans six bytes. The first set of data can begin at any memory location greater than or equal to 0x250 and end below 0x3CF. In order to program the LTC2983 with the custom thermistor table, both the resistance data and the Kelvin data are converted to 24-bit binary values. The sensor output resistance (units=Ω) follows the convention shown in Table 78, where the first 20 bits are the integer part and the remaining four bits are the fractional part. In order to simplify the temperature field, temperature values are input in Kelvin as an unsigned value, but the final temperatures reported by the LTC2983 are reported in °C or °F. The sensor temperature (Kelvin) follows the convention shown in Table 79, where the first 14 bits are the integer part and the remaining 10 bits are the fractional part. Table 77. NTC Thermistor Example Resistance vs Kelvin Data Memory Map POINT SENSOR OUTPUT TEMPERATURE START RESISTANCE(Ω) (K) ADDRESS STOP ADDRESS P0 0 457.5 0x2C8 0x2CD P1 80 400.2 0x2CE 0x2D3 P2 184 372.3 0x2D4 0x2D9 P3 423.2 320.1 0x2DA 0x2DF P4 973.36 290.55 0x2E0 0x2E5 P5 2238.728 249.32 0x2E6 0x2EB P6 5149.0744 240.3 0x2EC 0x2F1 P7 26775.18688 230 0x2F2 0x2F7 P8 139230.9718 215.3 0x2F8 0x2FD P9 724001.0532 200 0x2FE 0x303 BYTE 1 BYTE 2 BYTE 3 BYTE 1 Resistance Data BYTE 2 BYTE 3 Temperature Data Table 78. Example Thermistor Resistance Values BYTE 1 BYTE 2 BYTE 3 B23 B22 B21 B20 B19 B18 B17 B16 B15 B14 B13 B12 B11 B10 B9 Resistance 219 218 217 0 0 0 0 216 0 215 214 213 212 211 210 0 0 0 0 0 0 B8 B7 B6 B5 B4 B3 B2 29 28 27 26 25 24 23 22 21 20 2–1 2–2 2–3 2–4 0 0 0 0 0 0 0 0 0 0 0 0 B1 0 B0 0 80 0 0 0 0 0 0 0 0 0 0 0 0 0 1 0 1 0 0 0 0 0 0 0 0 184 0 0 0 0 0 0 0 0 0 0 0 0 1 0 1 1 1 0 0 0 0 0 0 0 423.2 0 0 0 0 0 0 0 0 0 0 0 1 1 0 1 0 0 1 1 1 0 0 1 1 973.36 0 0 0 0 0 0 0 0 0 0 1 1 1 1 0 0 1 1 0 1 0 1 0 1 2238.728 0 0 0 0 0 0 0 0 1 0 0 0 1 0 1 1 1 1 1 0 1 0 1 1 5149.074 0 0 0 0 0 0 0 1 0 1 0 0 0 0 0 1 1 1 0 1 0 0 0 1 26775.19 0 0 0 0 0 1 1 0 1 0 0 0 1 0 0 1 0 1 1 1 0 0 1 1 139231 0 0 1 0 0 0 0 1 1 1 1 1 1 1 0 1 1 1 1 1 0 0 0 0 724001.1 1 0 1 1 0 0 0 0 1 1 0 0 0 0 1 0 0 0 0 1 0 0 0 1 66 2983fc For more information www.linear.com/LTC2983 LTC2983 CUSTOM THERMISTORS starting address (offset from 0x250) is entered in the custom thermistor data pointer field of the channel assignment data. The table data length –1 (9 in this case) is entered into the custom thermistor data length field of the thermistor channel assignment word. In this example, a custom thermistor tied to CH5, with a sense resistor on CH3/4, is programmed with the channel assignment data shown in Table 80 (refer to Figure 24 for similar format). In this case the custom data begins at memory location 0x2C8 (starting address is 20). The Table 79. Example Thermistor Temperature Values BYTE 1 Temperature 457.5 BYTE 2 BYTE 3 B23 B22 B21 B20 B19 B18 B17 B16 B15 B14 B13 B12 B11 B10 B9 B8 B7 B6 B5 B4 B3 B2 B1 B0 213 212 211 210 29 28 27 26 25 24 23 22 21 20 2–1 2–2 2–3 2–4 2–5 2–6 2–7 2–8 2–9 2–10 0 0 0 0 0 1 1 1 0 0 1 0 0 1 1 0 0 0 0 0 0 0 0 0 400.2 0 0 0 0 0 1 1 0 0 1 0 0 0 0 0 0 1 1 0 0 1 1 0 0 372.3 0 0 0 0 0 1 0 1 1 1 0 1 0 0 0 1 0 0 1 1 0 0 1 1 320.1 0 0 0 0 0 1 0 1 0 0 0 0 0 0 0 0 0 1 1 0 0 1 1 0 290.55 0 0 0 0 0 1 0 0 1 0 0 0 1 0 1 0 0 0 1 1 0 0 1 1 249.32 0 0 0 0 0 0 1 1 1 1 1 0 0 1 0 1 0 1 0 0 0 1 1 1 240.3 0 0 0 0 0 0 1 1 1 1 0 0 0 0 0 1 0 0 1 1 0 0 1 1 230 0 0 0 0 0 0 1 1 1 0 0 1 1 0 0 0 0 0 0 0 0 0 0 0 215.3 0 0 0 0 0 0 1 1 0 1 0 1 1 1 0 1 0 0 1 1 0 0 1 1 200 0 0 0 0 0 0 1 1 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 Table 80. Custom Thermistor Channel Assignment Data CONFIGURATION FIELD DESCRIPTION # BITS BINARY DATA (1) Thermistor Type Custom Table 5 11011 1 1 0 1 1 (2) Sense Resistor Channel Pointer CH4 5 00100 Single-Ended 3 100 1µA 4 0011 Set These Bits to 0 3 00 (5) Custom Thermistor Start Address Data Pointer = 20 6 010100 (5) Custom Thermistor Length –1 = 9 Length-1 6 001001 (3) Sensor Configuration (4) Excitation Current Not Used MEMORY ADDRESS 210 MEMORY ADDRESS 211 MEMORY ADDRESS 212 MEMORY ADDRESS 213 0 0 1 0 0 1 0 0 0 0 1 1 0 0 0 0 1 0 1 0 0 0 0 1 0 0 1 2983fc For more information www.linear.com/LTC2983 67 LTC2983 CUSTOM THERMISTORS In addition to custom table driven thermistors, it is also possible to directly input Steinhart-Hart coefficients into the LTC2983 (thermistor type 11010, see Table 51). Steinhart-Hart coefficients are commonly specified parameters provided by thermistor manufacturers. The Steinhart-Hart equation is: Steinhart-Hart data is stored sequentially in any memory location greater than or equal to 0x250 and below 0x3CF. Each coefficient is represented by a standard, singleprecision, IEEE754 32-bit value (see Table 81). 1 = A +B •ln(R)+C •ln(R)2 +D•ln(R)3 +E •ln(R)4 T 5 +F •ln(R) In this example a Steinhart-Hart equation is entered into memory starting at location 0x300 (see Table 82). Example Custom Steinhart-Hart Thermistor Table 81. Steinhart-Hart Custom Thermistor Data Format ADDRESS COEFFICIENT VALUE 0x250 + 4 *Start Address A 32-Bit Single-Precision Floating Point Format 0x250 + 4 *Start Address + 4 B 32-Bit Single-Precision Floating Point Format 0x250 + 4 *Start Address + 8 C 32-Bit Single-Precision Floating Point Format 0x250 + 4 *Start Address + 12 D 32-Bit Single-Precision Floating Point Format 0x250 + 4 *Start Address + 16 E 32-Bit Single-Precision Floating Point Format 0x250 + 4 *Start Address + 20 F 32-Bit Single-Precision Floating Point Format Table 82. Custom Steinhart-Hart Data Example COEFFICIENT VALUE START SIGN ADDRESS MSB EXPONENT MANTISSA LSB MSB LSB A 1.45E-03 0x300 0 0 1 1 1 0 1 0 1 0 1 1 1 1 1 0 0 0 0 0 1 1 0 1 1 1 1 0 1 1 0 1 B 2.68E-04 0x304 0 0 1 1 1 0 0 1 1 0 0 0 1 1 0 0 1 0 0 0 0 0 1 0 0 1 0 1 1 0 1 0 C 0 0x308 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 D 1.64E-07 0x30C 0 0 1 1 0 1 0 0 0 0 1 1 0 0 0 0 0 0 0 1 0 1 1 1 1 1 1 1 1 0 1 0 E 0 0x310 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 F 0 0x314 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 68 2983fc For more information www.linear.com/LTC2983 LTC2983 CUSTOM THERMISTORS Table 83. Custom Steinhart-Hart Channel Assignment Data CONFIGURATION FIELD DESCRIPTION # BITS BINARY DATA (1) Thermistor Type Custom Steinhart-Hart 5 11010 1 1 0 1 0 (2) Sense Resistor Channel Pointer CH4 5 00100 Single-Ended 3 100 1µA 4 0011 Set These Bits to 0 3 00 (5) Custom Thermistor Start Address Data Pointer = 30 6 011110 (5) Custom SteinhartHart Length Always Set to 0 6 000000 (3) Sensor Configuration (4) Excitation Current Not Used Fixed at Six 32-Bit Words MEMORY ADDRESS 210 MEMORY ADDRESS 211 MEMORY ADDRESS 212 MEMORY ADDRESS 213 0 0 1 0 0 A custom thermistor tied to CH5, with a sense resistor on CH3/4, is programmed with the channel assignment data shown in Table 83 (refer to Figure 24 for a similar format). In this case the custom data begins at memory location 0x26E (starting address is 30). The starting address (offset from 0x250) is entered in the custom thermistor data pointer field of the channel assignment data. The data length (set to 0) is always six 32-bit floating point words. Universal Sensor Hardware The LTC2983 can be configured as a universal temperature measurement device. Up to four sets of universal inputs can be applied to a single LTC2983. Each of these sets can directly digitize a 3-wire RTD, 4-Wire RTD, Thermistor, or thermocouple without changing any on board hardware (see Figure 42). Each sensor can share the same four ADC inputs and protection/filtering circuitry are configured using software changes (new channel assignment data) only. One sense resistor and cold junction sensor are shared among all four banks of sensors. 1 0 0 0 0 1 1 0 0 0 0 1 1 1 1 0 0 0 0 0 0 0 The LTC2983 includes many flexible, software configurable input modes. In order to share four common inputs among all four sensor types each sensor requires specific configuration bits (see Table 84). 3-Wire RTDs are configured with shared RSENSE, 4-Wire RTDs and thermistors are configured as shared and/or rotated, thermocouples are configured differential with internal ground, and diodes are configured as single-ended. Table 84. Sensor Configuration for Universal Hookup SENSOR TYPE CONFIGURATION OPTIONS CONFIGURATION BITS SEE TABLE 3-WIRE RTD Share B18 = 1, B19 = 0 Table 28 4-WIRE RTD Share B18 = 1, B19 = 0 Table 28 4-WIRE RTD Rotate B18 = 0, B19 = 1 Table 28 Thermistor Share B19 = 0, B20 = 1 Table 52 Thermistor Rotate B19 = 1, B20 = 0 Table 52 Thermocouple Single-Ended B21 = 1 Table 14 Diode Single-Ended B26 = 1 Table 17 2983fc For more information www.linear.com/LTC2983 69 LTC2983 PACKAGE DESCRIPTION Please refer to http://www.linear.com/product/LTC2938#packaging for the most recent package drawings. LX Package 48-Lead Plastic LQFP (7mm × 7mm) (Reference LTC DWG # 05-08-1760 Rev A) 7.15 – 7.25 9.00 BSC 5.50 REF 7.00 BSC 48 0.50 BSC 1 2 48 SEE NOTE: 4 1 2 9.00 BSC 5.50 REF 7.00 BSC 7.15 – 7.25 0.20 – 0.30 A A PACKAGE OUTLINE C0.30 – 0.50 1.30 MIN RECOMMENDED SOLDER PAD LAYOUT APPLY SOLDER MASK TO AREAS THAT ARE NOT SOLDERED 1.60 1.35 – 1.45 MAX 11° – 13° R0.08 – 0.20 GAUGE PLANE 0.25 0° – 7° 11° – 13° 0.09 – 0.20 1.00 REF 0.50 BSC 0.17 – 0.27 0.05 – 0.15 0.45 – 0.75 SECTION A – A COMPONENT PIN “A1” TRAY PIN 1 BEVEL 70 XXYY LTCXXXX LX-ES Q_ _ _ _ _ _ e3 NOTE: 1. PACKAGE DIMENSIONS CONFORM TO JEDEC #MS-026 PACKAGE OUTLINE 2. DIMENSIONS ARE IN MILLIMETERS 3. DIMENSIONS OF PACKAGE DO NOT INCLUDE MOLD FLASH. MOLD FLASH SHALL NOT EXCEED 0.25mm ON ANY SIDE, IF PRESENT 4. PIN-1 INDENTIFIER IS A MOLDED INDENTATION, 0.50mm DIAMETER 5. DRAWING IS NOT TO SCALE LX48 LQFP 0113 REV A PACKAGE IN TRAY LOADING ORIENTATION 2983fc Information furnished by Linear Technology Corporation is believed to be accurate and reliable. However, no responsibility is assumed for its use. Linear Technology Corporation makes no representaFor more information www.linear.com/LTC2983 tion that the interconnection of its circuits as described herein will not infringe on existing patent rights. LTC2983 REVISION HISTORY REV DATE DESCRIPTION A 07/15 Removed Tape and Reel options PAGE NUMBER 3 Added Absolute Maximum Ratings for Q1, Q2, Q3, LDO, VREFOUT, VREF_BYP 3 Changed reference Output Voltage Temperature Coefficient 4 Changed Error Contribution for thermocouples 13 Changed filter capacitor values in Figures 9, 12, 15, 18, 19, 21 B 09/15 Revised Table 2A. Memory Map 14 Revised the following tables so that all bytes contain eight bits: Table 69, 70, 74, 75, 78, 79 C 01/16 33, 35, 37, 39, 40, 42 Added H-Grade option 60, 61, 63, 64, 66, 67 3, 4 2983fc For more information www.linear.com/LTC2983 71 LTC2983 TYPICAL APPLICATION 2.85V TO 5.25V SHARE WITH ALL FOUR SETS OF SENSORS THERMOCOUPLE THERMISTOR 3-WIRE RTD 3 2 4-WIRE RTD 16 RSENSE 17 CH1 2, 4, 6, 8, 45 VDD CH2 0.1µF 48 Q1 47 Q2 4 3 18 2 46 Q3 CH3 10µF 10µF LTC2983 1 19 2 1 1 CH4 13 VREFOUT 14 VREFP 20 21 1µF CH5 CH6 11 VREF_BYP 1µF THREE MORE SETS OF UNIVERSAL SENSOR INPUTS 22 TO 35 CH7 TO CH20 36 (OPTIONAL DRIVE LOW TO RESET) 42 41 40 SPI INTERFACE 39 38 43 LDO 10µF COM RESET CS 37 INTERRUPT 1, 3, 5, 7, 9, 12, 15, 44 GND SDI SDO SCK 2983 F42 Figure 42. Universal Inputs Allow Common Hardware Sharing for Thermocouples, Diodes, Thermistors, 3-Wire RTDs, and 4-Wire RTDs RELATED PARTS PART NUMBER DESCRIPTION LTC2984 Multi-Sensor High Accuracy Digital Pin/Software Compatible Version of LTC2983 with Integrated EEPROM Temperature Measurement System with EEPROM COMMENTS LTC2990 Quad I2C Temperature, Voltage and Current Monitor Remote and Internal Temperatures, 14-Bit Voltages and Current, Internal 10ppm/°C Reference LTC2991 Octal I2C Voltage, Current, Temperature Monitor Remote and Internal Temperatures, 14-Bit Voltages and Current, Internal 10ppm/°C Reference LTC2995 Temperature Sensor and Voltage Monitor with Alert Outputs Monitors Temperature and Two Voltages, Adjustable Thresholds, Open Drain Alert Outputs, Temperature to Voltage Output with Integrated 1.8V Reference, ±1°C (Max) Accuracy LTC2996 Temperature Sensor with Alert Outputs Monitors Temperature, Adjustable Thresholds, Open Drain Alert Outputs, Temperature to Voltage Output with Integrated 1.8V Reference, ±1°C (Max) Accuracy LTC2997 Remote/Internal Temperature Sensor Temperature to Voltage Output with Integrated 1.8V Reference, ±1°C (Max) Accuracy LTC2943 20V I2C Coulomb Counter Monitors Charge, Current, Voltage and Temperature with 1% Accuracy. Works with Any Battery Chemistry and Capacity 72 Linear Technology Corporation 1630 McCarthy Blvd., Milpitas, CA 95035-7417 For more information www.linear.com/LTC2983 (408) 432-1900 ● FAX: (408) 434-0507 ● www.linear.com/LTC2983 2983fc LT 0116 REV C• PRINTED IN USA LINEAR TECHNOLOGY CORPORATION 2014