±0.25°C Accurate, 16-Bit Digital I2C Temperature Sensor ADT7420 Data Sheet FEATURES GENERAL DESCRIPTION High performance Temperature accuracy ±0.20°C from −10°C to +85°C at 3.0 V ±0.25°C from −20°C to +105°C from 2.7 V to 3.3 V 16-bit resolution: 0.0078°C Ultralow temperature drift: 0.0073°C NIST traceable or equivalent Fast first temperature conversion on power-up of 6 ms Easy implementation No temperature calibration/correction required by user No linearity correction required Low power Power-saving 1 sample per second (SPS) mode 700 µW typical at 3.3 V in normal mode 7 µW typical at 3.3 V in shutdown mode Wide operating ranges Temperature range: −40°C to +150°C Voltage range: 2.7 V to 5.5 V Programmable interrupts Critical overtemperature interrupt Overtemperature/undertemperature interrupt I2C-compatible interface 16-lead, 4 mm × 4 mm LFCSP RoHS-compliant package The ADT7420 is a high accuracy digital temperature sensor offering breakthrough performance over a wide industrial range, housed in a 4 mm × 4 mm LFCSP package. It contains an internal band gap reference, a temperature sensor, and a 16-bit ADC to monitor and digitize the temperature to 0.0078°C resolution. The ADC resolution, by default, is set to 13 bits (0.0625°C). The ADC resolution is a user programmable mode that can be changed through the serial interface. The ADT7420 is guaranteed to operate over supply voltages from 2.7 V to 5.5 V. Operating at 3.3 V, the average supply current is typically 210 μA. The ADT7420 has a shutdown mode that powers down the device and offers a shutdown current of typically 2.0 μA at 3.3 V. The ADT7420 is rated for operation over the −40°C to +150°C temperature range. Pin A0 and Pin A1 are available for address selection, giving the ADT7420 four possible I2C addresses. The CT pin is an opendrain output that becomes active when the temperature exceeds a programmable critical temperature limit. The INT pin is also an open-drain output that becomes active when the temperature exceeds a programmable limit. The INT pin and CT pin can operate in comparator and interrupt event modes. PRODUCT HIGHLIGHTS APPLICATIONS 1. 2. 3. 4. RTD and thermistor replacement Thermocouple cold junction compensation Medical equipment Industrial control and test Food transportation and storage Environmental monitoring and HVAC Laser diode temperature control 5. Ease of use, no calibration or correction required by the user. Low power consumption. Excellent long-term stability and reliability. High accuracy for industrial, instrumentation, and medical applications. Packaged in a 16-lead, 4 mm × 4 mm LFCSP RoHScompliant package. FUNCTIONAL BLOCK DIAGRAM A0 3 A1 4 CONFIGURATION REGISTER TEMPERATURE VALUE REGISTER INTERNAL OSCILLATOR TLOW REGISTER TCRIT REGISTER INTERNAL REFERENCE THYST REGISTER THIGH REGISTER TEMPERATURE SENSOR ID REGISTER STATUS REGISTER SOFTWARE RESET REGISTER POINTER REGISTER Σ-Δ MODULATOR ADT7420 FILTER LOGIC I2C INTERFACE 10 CT 9 INT 1 SCL 2 SDA TCRIT THIGH TLOW 09013-001 VDD 12 11 GND Figure 1. Rev. 0 Document Feedback Information furnished by Analog Devices is believed to be accurate and reliable. However, no responsibility is assumed by Analog Devices for its use, nor for any infringements of patents or other rights of third parties that may result from its use. Specifications subject to change without notice. No license is granted by implication or otherwise under any patent or patent rights of Analog Devices. Trademarks and registered trademarks are the property of their respective owners. One Technology Way, P.O. Box 9106, Norwood, MA 02062-9106, U.S.A. Tel: 781.329.4700 ©2012 Analog Devices, Inc. All rights reserved. Technical Support www.analog.com ADT7420 Data Sheet TABLE OF CONTENTS Features .............................................................................................. 1 Temperature Value Registers .................................................... 13 Applications ....................................................................................... 1 Status Register ............................................................................. 14 General Description ......................................................................... 1 Configuration Register .............................................................. 14 Product Highlights ........................................................................... 1 THIGH Setpoint Registers ............................................................. 15 Functional Block Diagram .............................................................. 1 TLOW Setpoint Registers.............................................................. 15 Revision History ............................................................................... 2 TCRIT Setpoint Registers.............................................................. 15 Specifications..................................................................................... 3 THYST Setpoint Register............................................................... 16 I C Timing Specifications ............................................................ 5 ID Register................................................................................... 16 Absolute Maximum Ratings ............................................................ 6 Serial Interface ................................................................................ 17 ESD Caution .................................................................................. 6 Serial Bus Address ...................................................................... 17 Pin Configuration and Function Descriptions ............................. 7 Writing Data ............................................................................... 18 Typical Performance Characteristics ............................................. 8 Reading Data ............................................................................... 19 Theory of Operation ...................................................................... 10 Reset ............................................................................................. 20 Circuit Information .................................................................... 10 General Call ................................................................................ 20 Converter Details........................................................................ 10 INT and CT Outputs...................................................................... 21 Normal Mode .............................................................................. 10 Undertemperature and Overtemperature Detection ............ 21 One-Shot Mode .......................................................................... 10 Applications Information .............................................................. 23 1 SPS Mode .................................................................................. 11 Thermal Response Time ........................................................... 23 Shutdown ..................................................................................... 11 Supply Decoupling ..................................................................... 23 Fault Queue ................................................................................. 11 Powering from a Switching Regulator ..................................... 23 Temperature Data Format ......................................................... 12 Temperature Measurement ....................................................... 23 Temperature Conversion Formulas ......................................... 12 Quick Guide to Measuring Temperature ................................ 23 Registers ........................................................................................... 13 Outline Dimensions ....................................................................... 24 Address Pointer Register ........................................................... 13 Ordering Guide .......................................................................... 24 2 REVISION HISTORY 12/12—Revision 0: Initial Version Rev. 0 | Page 2 of 24 Data Sheet ADT7420 SPECIFICATIONS TA = −40°C to +125°C, VDD = 2.7 V to 5.5 V, unless otherwise noted. Table 1. Parameter TEMPERATURE SENSOR AND ADC Accuracy 1 Min Typ Max Unit Test Conditions/Comments 0.0017 ±0.20 2 ±0.25 ±0.31 ±0.35 ±0.50 ±0.50 3 ±0.66 −0.85 −1.0 13 °C °C °C °C °C °C °C °C °C Bits 16 Bits TA = −10°C to +85°C, VDD = 3.0 V TA = −20°C to +105°C, VDD = 2.7 V to 3.3 V TA = −40°C to +105°C, VDD = 3.0 V TA = −40°C to +105°C, VDD = 2.7 V to 3.3 V TA = −40°C to +125°C, VDD = 2.7 V to 3.3 V TA = −10°C to +105°C, VDD = 4.5 V to 5.5 V TA = −40°C to +125°C, VDD = 4.5 V to 5.5 V TA = +150°C, VDD = 4.5 V to 5.5 V TA = +150°C, VDD = 2.7 V to 3.3 V Twos complement temperature value of the sign bit plus 12 ADC bits (power-up default resolution) Twos complement temperature value of the sign bit plus 15 ADC bits (Bit 7 = 1 in the configuration register) Temperature Resolution 13-Bit 16-Bit Temperature Conversion Time 0.0625 0.0078 240 °C °C ms Fast Temperature Conversion Time 1 SPS Conversion Time Temperature Hysteresis 4 6 60 ±0.002 ms ms °C ±0.015 0.0073 0.1 °C °C °C/V ADC Resolution Repeatability 5 Drift 6 DC PSRR DIGITAL OUTPUTS (CT, INT, SDA—OPEN DRAIN) High Output Leakage Current, IOH Output Low Voltage, VOL Output High Voltage, VOH Output Capacitance, COUT DIGITAL INPUTS (SCL, SDA, A0, A1) Input Current Input Low Voltage, VIL 5 0.4 µA V V pF CT and INT pins pulled up to 5.5 V IOL = 3 mA at 5.5 V, IOL = 1 mA at 3.3 V ±1 0.3 × VDD 0.4 µA V V V V ns VIN = 0 V to VDD SCL and SDA only A0 and A1 only SCL and SDA only A0 and A1 only Input filtering suppresses noise spikes of less than 50 ns 10 pF 5.5 V 210 265 µA At 5.5 V 250 300 µA 1 SPS Current At 3.3 V At 5.5 V 46 65 Input High Voltage, VIH 0.1 13-bit resolution (sign + 12-bit) 16-bit resolution (sign + 15-bit) Continuous conversion and one-shot conversion modes First conversion on power-up only Conversion time for 1 SPS mode Temperature cycle = 25°C to 125°C and back to 25°C TA = 25°C 500 hour stress test at +150°C with VDD = 5.0 V TA = 25°C 0.7 × VDD 2 0.7 × VDD 2 SCL, SDA Glitch Rejection Pin Capacitance POWER REQUIREMENTS Supply Voltage Supply Current At 3.3 V 50 2 2.7 Rev. 0 | Page 3 of 24 µA µA Peak current while converting, I2C interface inactive Peak current while converting, I2C interface inactive VDD = 3.3 V, 1 SPS mode, TA = 25°C VDD = 5.5 V, 1 SPS mode, TA = 25°C ADT7420 Parameter Shutdown Current At 3.3 V At 5.5 V Power Dissipation Normal Mode Power Dissipation 1 SPS Data Sheet Min Typ Max Unit Test Conditions/Comments 2.0 5.2 700 150 15 25 µA µA µW µW Supply current in shutdown mode Supply current in shutdown mode VDD = 3.3 V, normal mode at 25°C Power dissipated for VDD = 3.3 V, TA = 25°C Accuracy specification includes repeatability. The equivalent 3 σ limits are ±0.15°C. This 3 σ specification is provided to enable comparison with other vendors who use these limits. For higher accuracy at 5 V operation, contact Analog Devices, Inc. 4 Temperature Hysteresis does not include repeatability. 5 Based on a floating average of 10 readings. 6 Drift includes solder heat resistance and life time test performed as per JEDEC Standard JESD22-A108. 1 2 3 Rev. 0 | Page 4 of 24 Data Sheet ADT7420 I2C TIMING SPECIFICATIONS TA = −40°C to +150°C, VDD = 2.7 V to 5.5 V, unless otherwise noted. All input signals are specified with rise time (tR) = fall time (tF) = 5 ns (10% to 90% of VDD) and timed from a voltage level of 1.6 V. Table 2. Parameter SERIAL INTERFACE1 SCL Frequency SCL High Pulse Width, tHIGH SCL Low Pulse Width, tLOW SCL, SDA Rise Time, tR SCL, SDA Fall Time, tF Hold Time (Start Condition), tHD:STA Setup Time (Start Condition), tSU:STA Data Setup Time, tSU:DAT Setup Time (Stop Condition), tSU:STO Data Hold Time, tHD:DAT (Master) Bus-Free Time (Between Stop and Start Condition), tBUF Capacitive Load for Each Bus Line, CB 1 Min 0 0.6 1.3 Typ Max Unit 400 kHz μs μs μs μs μs μs μs μs μs μs pF 0.3 0.3 0.6 0.6 0.02 0.6 0.03 1.3 400 Test Conditions/Comments See Figure 2 After this period, the first clock is generated Relevant for repeated start condition Sample tested during initial release to ensure compliance. Timing Diagram tLOW tR tF tHD:STA SCL tHD:STA tHD:DAT tHIGH tSU:STA tSU:DAT tSU:STO tBUF P S S Figure 2. Serial Interface Timing Diagram Rev. 0 | Page 5 of 24 P 09013-002 SDA ADT7420 Data Sheet ABSOLUTE MAXIMUM RATINGS Table 3. Parameter VDD to GND SDA Voltage to GND SCL Output Voltage to GND A0 Input Voltage to GND A1 Input Voltage to GND CT and INT Output Voltage to GND ESD Rating (Human Body Model) Operating Temperature Range1 Storage Temperature Range Maximum Junction Temperature, TJMAX 16-Lead LFCSP (CP-16-17) Power Dissipation2 Thermal Impedance4 θJA, Junction-to-Ambient (Still Air) θJC, Junction-to-Case IR Reflow Soldering Peak Temperature (RoHS-Compliant Package) Time at Peak Temperature Ramp-Up Rate Ramp-Down Rate Time from 25°C to Peak Temperature Rating −0.3 V to +7 V −0.3 V to VDD + 0.3 V −0.3 V to VDD + 0.3 V −0.3 V to VDD + 0.3 V −0.3 V to VDD + 0.3 V −0.3 V to VDD + 0.3 V 2.0 kV −40°C to +150°C −65°C to +160°C 150°C Stresses above those listed under Absolute Maximum Ratings may cause permanent damage to the device. This is a stress rating only; functional operation of the device at these or any other conditions above those indicated in the operational section of this specification is not implied. Exposure to absolute maximum rating conditions for extended periods may affect device reliability. ESD CAUTION WMAX = (TJMAX − TA3)/θJA 37°C/W 33°C/W 220°C 260°C (+0°C/−5°C) 20 sec to 40 sec 3°C/sec maximum −6°C/sec maximum 8 minutes maximum Sustained operation above 125°C results in a shorter product lifetime. For more information, contact Analog Devices. 2 Values relate to package being used on a standard 2-layer PCB. This gives a worst-case θJA and θJC. 3 TA = ambient temperature. 4 Junction-to-case resistance is applicable to components featuring a preferential flow direction, for example, components mounted on a heat sink. Junction-to-ambient is more useful for air-cooled, PCB-mounted components. 1 Rev. 0 | Page 6 of 24 Data Sheet ADT7420 14 NC 13 NC 16 NC 15 NC PIN CONFIGURATION AND FUNCTION DESCRIPTIONS 17 EP SCL 1 A0 3 ADT7420 TOP VIEW (Not to Scale) 11 GND 10 CT 9 INT NC 7 NC 8 NC 5 NC 6 A1 4 NOTES 1. NC = NO CONNECT. THE NC PIN IS NOT BONDED TO THE DIE INTERNALLY. 2. TO ENSURE CORRECT OPERATION, THE EXPOSED PAD SHOULD EITHER BE LEFT FLOATING OR CONNECTED TO GROUND. 09013-004 SDA 2 12 VDD Figure 3. Pin Configuration Table 4. Pin Function Descriptions Pin No. 1 Mnemonic SCL 2 SDA 3 4 5 6 7 8 9 A0 A1 NC NC NC NC INT 10 CT 11 12 13 14 15 16 17 GND VDD NC NC NC NC EP Description I2C Serial Clock Input. The serial clock is used to clock in and clock out data to and from any register of the ADT7420. Open-drain configuration. A pull-up resistor is required, typically 10 kΩ. I2C Serial Data Input/Output. Serial data to and from the part is provided on this pin. Open-drain configuration. A pull-up resistor is required, typically 10 kΩ. I2C Serial Bus Address Selection Pin. Logic input. Connect to GND or VDD to set an I2C address. I2C Serial Bus Address Selection Pin. Logic input. Connect to GND or VDD to set an I2C address. No Connect. The NC pin is not bonded to the die internally. No Connect. The NC pin is not bonded to the die internally. No Connect. The NC pin is not bonded to the die internally. No Connect. The NC pin is not bonded to the die internally. Overtemperature and Undertemperature Indicator. Logic output. Power-up default setting is as an active low comparator interrupt. Open-drain configuration. A pull-up resistor is required, typically 10 kΩ. Critical Overtemperature Indicator. Logic output. Power-up default polarity is active low. Open-drain configuration. A pull-up resistor is required, typically 10 kΩ. Analog and Digital Ground. Positive Supply Voltage (2.7 V to 5.5 V). The supply should be decoupled with a 0.1 μF ceramic capacitor to ground. No Connect. The NC pin is not bonded to the die internally. No Connect. The NC pin is not bonded to the die internally. No Connect. The NC pin is not bonded to the die internally. No Connect. The NC pin is not bonded to the die internally. Exposed Pad. To ensure correct operation, the exposed pad should either be left floating or connected to ground. Rev. 0 | Page 7 of 24 ADT7420 Data Sheet TYPICAL PERFORMANCE CHARACTERISTICS 30 1.00 25 0.50 SHUTDOWN IDD (µA) MAX ACCURACY LIMITS 0.25 0 –0.25 MAX ACCURACY LIMITS 20 15 10 5.5V 5.0V –0.50 5 4.5V –40 –20 80 60 20 40 TEMPERATURE (°C) 0 100 120 140 0 –100 09013-027 –1.00 –60 –50 0 50 100 150 200 TEMPERATURE (°C) Figure 7. Shutdown Current vs. Temperature Figure 4. Temperature Accuracy at 3 V 300 1.00 0.75 IDD CONTINUOUS CONVERSION 250 MAX ACCURACY LIMITS 0.50 200 0.25 IDD (µA) TEMPERATURE ERROR (°C) 3.3V 3.0V 2.7V 3.6V –0.75 09013-032 TEMPERATURE ERROR (°C) 0.75 0 –0.25 150 100 –0.50 IDD 1SPS MAX ACCURACY LIMITS 50 –40 –20 60 80 20 40 TEMPERATURE (°C) 0 100 120 140 0 2.5 09013-026 –1.00 –60 3.0 3.5 4.0 4.5 5.0 5.5 6.0 SUPPLY VOLTAGE (V) Figure 5. Temperature Accuracy at 5 V 09013-029 –0.75 Figure 8. Average Operating Supply Current vs. Supply Voltage 8 300 5.5V CONTINUOUS CONVERSION 250 7 6 100 –50 0 4 3 5.5V 1SPS 2 3.0V 1SPS 1 50 0 –100 5 50 100 150 TEMPERATURE (°C) 200 0 2.5 3.0 3.5 4.0 4.5 5.0 5.5 SUPPLY VOLTAGE (V) Figure 9. Shutdown Current vs. Supply Voltage Figure 6. Operating Supply Current vs. Temperature Rev. 0 | Page 8 of 24 6.0 09013-210 150 09013-028 IDD (µA) SHUTDOWN IDD (µA) 3.0V CONTINUOUS CONVERSION 200 Data Sheet ADT7420 140 125°C 120 85°C 80 IT TAKES LESS THAN 2 SECONDS TO REACH 63.2% OF ITS TEMPERATURE SPAN 60 40 20 0 0 5 10 15 TIME (s) 20 25 09013-110 DUT TEMPERATURE (°C) 105°C 100 Figure 10. Thermal Response Time Rev. 0 | Page 9 of 24 ADT7420 Data Sheet THEORY OF OPERATION CIRCUIT INFORMATION NORMAL MODE The ADT7420 is a high accuracy digital temperature sensor that uses a 16-bit ADC to monitor and digitize the temperature to 0.0078°C of resolution. The ADC resolution, by default, is set to 13 bits (0.0625°C). An internal temperature sensor generates a voltage proportional to absolute temperature, which is compared to an internal voltage reference and input into a precision digital modulator. In normal mode (default power-up mode) the ADT7420 runs an automatic conversion sequence. During this automatic conversion sequence, a conversion typically takes 240 ms to complete and the ADT7420 is continuously converting. This means that as soon as one temperature conversion is completed, another temperature conversion begins. Each temperature conversion result is stored in the temperature value registers and is available through the I2C interface. In continuous conversion mode, the read operation provides the most recent converted result. The internal temperature sensor has high accuracy and linearity over the entire rated temperature range without needing correction or calibration by the user. The sensor output is digitized by a sigma-delta (Σ-Δ) modulator, also known as the charge balance type analog-to-digital converter. This type of converter utilizes time-domain oversampling and a high accuracy comparator to deliver 16 bits of resolution in an extremely compact circuit. CONVERTER DETAILS The Σ-Δ modulator consists of an input sampler, a summing network, an integrator, a comparator, and a 1-bit DAC. This architecture creates a negative feedback loop and minimizes the integrator output by changing the duty cycle of the comparator output in response to input voltage changes. The comparator samples the output of the integrator at a much higher rate than the input sampling frequency. This oversampling spreads the quantization noise over a much wider band than that of the input signal, improving overall noise performance and increasing accuracy. The measured temperature value is compared with a critical temperature limit (stored in the 16-bit TCRIT setpoint read/write register), a high temperature limit (stored in the 16-bit THIGH setpoint read/write register), and a low temperature limit (stored in the 16-bit TLOW setpoint read/write register). If the measured value exceeds these limits, the INT pin is activated; and if it exceeds the TCRIT limit, the CT pin is activated. The INT and CT pins are programmable for polarity via the configuration register, and the INT and CT pins are also programmable for interrupt mode via the configuration register. Setting Bit 6 to 0 and Bit 5 to 1 of the configuration register (Register Address 0x03) enables the one-shot mode. When this mode is enabled, the ADT7420 immediately completes a conversion and then goes into shutdown mode. INTEGRATOR COMPARATOR VOLTAGE REF AND VPTAT Wait for a minimum of 240 ms after writing to the operation mode bits before reading back the temperature from the temperature value register. This time ensures that the ADT7420 has time to power up and complete a conversion. 1-BIT DAC 13-BIT/ 16-BIT TEMPERATURE VALUE REGISTER Figure 11. Σ-Δ Modulator The ADT7420 can be configured to operate in any one of the following four operating modes: normal, one-shot, 1 SPS, and shutdown. 09013-012 1-BIT LPF DIGITAL FILTER The conversion clock for the part is generated internally. No external clock is required except when reading from and writing to the serial port. ONE-SHOT MODE Σ-∆ MODULATOR CLOCK GENERATOR On power-up, the first conversion is a fast conversion, taking typically 6 ms. If the temperature exceeds 147°C, the CT pin asserts low. If the temperature exceeds 64°C, the INT pin asserts low. Fast conversion temperature accuracy is typically within ±5°C. To obtain an updated temperature conversion, reset Bit 6 to 0 and Bit 5 to 1 in the configuration register (0x03). The one-shot mode is useful when one of the circuit design priorities is to reduce power consumption. Rev. 0 | Page 10 of 24 Data Sheet ADT7420 CT and INT Operation in One-Shot Mode See Figure 12 for more information on one-shot CT pin operation for TCRIT overtemperature events when one of the limits is exceeded. Note that in interrupt mode, a read from any register resets the INT and CT pins. For the INT pin in the comparator mode, if the temperature drops below the THIGH – THYST value or goes above the TLOW + THYST value, a write to the operation mode bits (Bit 5 and Bit 6 of the configuration register, Register Address 0x03) resets the INT pin. For the CT pin in the comparator mode, if the temperature drops below the TCRIT – THYST value, a write to the operation mode bits (Bit 6 = 0 and Bit 5 = 1 of the configuration register, Register Address 0x03) resets the CT pin (see Figure 12). Note that when using one-shot mode, ensure that the refresh rate is appropriate to the application being used. 1 SPS MODE In this mode, the part performs one measurement per second. A conversion takes only 60 ms typically, and it remains in the idle state for the remaining 940 ms period. This mode is enabled by writing 1 to Bit 6 and 0 to Bit 5 of the configuration register (Register Address 0x03). SHUTDOWN The ADT7420 can be placed in shutdown mode by writing 1 to Bit 6 and 1 to Bit 5 of the configuration register (Register Address 0x03), in which case the entire IC is shut down and no further conversions are initiated until the ADT7420 is taken out of shutdown mode. The ADT7420 can be taken out of shutdown mode by writing 0 to Bit 6 and 0 to Bit 5 in the configuration register (Register Address 0x03). The ADT7420 typically takes 1 ms (with a 0.1 µF decoupling capacitor) to come out of shutdown mode. The conversion result from the last conversion prior to shutdown can still be read from the ADT7420 even when it is in shutdown mode. When the part is taken out of shutdown mode, the internal clock is started and a conversion is initiated. FAULT QUEUE Bit 0 and Bit 1 of the configuration register (Register Address 0x03) are used to set up a fault queue. The queue can facilitate up to four fault events to prevent false tripping of the INT and CT pins when the ADT7420 is used in a noisy temperature environment. The number of faults set in the queue must occur consecutively to set the INT and CT outputs. For example, if the number of faults set in the queue is four, then four consecutive temperature conversions must occur with each result exceeding a temperature limit in any of the limit registers before the INT and CT pins are activated. If two consecutive temperature conversions exceed a temperature limit and the third conversion does not, the fault count is reset back to zero. TEMPERATURE 149°C 148°C TCRIT 147°C 146°C 145°C 144°C 143°C TCRIT – THYST 142°C 141°C 140°C CT PIN POLARITY = ACTIVE LOW CT PIN POLARITY = ACTIVE HIGH TIME WRITE TO BIT 5 AND BIT 6 OF CONFIGURATION REGISTER.* WRITE TO BIT 5 AND BIT 6 OF CONFIGURATION REGISTER.* *THERE IS A 240ms DELAY BETWEEN WRITING TO THE CONFIGURATION REGISTER TO START A STANDARD ONE-SHOT CONVERSION AND THE CT PIN GOING ACTIVE. THIS IS DUE TO THE CONVERSION TIME. THE DELAY IS 60ms IN THE CASE OF A ONE-SHOT CONVERSION. Figure 12. One-Shot CT Pin Rev. 0 | Page 11 of 24 09013-013 WRITE TO BIT 5 AND BIT 6 OF CONFIGURATION REGISTER.* ADT7420 Data Sheet TEMPERATURE DATA FORMAT TEMPERATURE CONVERSION FORMULAS One LSB of the ADC corresponds to 0.0625°C in 13-bit mode or 0.0078°C in 16-bit mode. The ADC can theoretically measure a temperature range of 255°C, but the ADT7420 is guaranteed to measure a low value temperature limit of −40°C to a high value temperature limit of +150°C. The temperature measurement result is stored in the 16-bit temperature value register and is compared with the high temperature limits stored in the TCRIT setpoint register and the THIGH setpoint register. It is also compared with the low temperature limit stored in the TLOW setpoint register. 16-Bit Temperature Data Format Positive Temperature = ADC Code (dec)/128 Temperature data in the temperature value register, the TCRIT setpoint register, the THIGH setpoint register, and the TLOW setpoint register are represented by a 13-bit twos complement word. The MSB is the temperature sign bit. The three LSBs, Bit 0 to Bit 2, on power-up, are not part of the temperature conversion result and are flag bits for TCRIT, THIGH, and TLOW. Table 5 shows the 13-bit temperature data format without Bit 0 to Bit 2. The number of bits in the temperature data-word can be extended to 16 bits, twos complement, by setting Bit 7 to 1 in the configuration register (Register Address 0x03). When using a 16-bit temperature data value, Bit 0 to Bit 2 are not used as flag bits and are, instead, the LSB bits of the temperature value. The poweron default setting has a 13-bit temperature data value. Reading back the temperature from the temperature value register requires a 2-byte read. Designers that use a 9-bit temperature data format can still use the ADT7420 by ignoring the last four LSBs of the 13-bit temperature value. These four LSBs are Bit 6 to Bit 3 in Table 5. Table 5. 13-Bit Temperature Data Format Temperature −40°C −25°C −0.0625°C 0°C +0.0625°C +25°C +105°C +125°C +150°C Digital Output (Binary) Bits[15:3] 1 1101 1000 0000 1 1110 0111 0000 1 1111 1111 1111 0 0000 0000 0000 0 0000 0000 0001 0 0001 1001 0000 0 0110 1001 0000 0 0111 1101 0000 0 1001 0110 0000 Digital Output (Hex) 0x1D80 0x1E70 0x1FFF 0x000 0x001 0x190 0x690 0x7D0 0x960 Negative Temperature = (ADC Code (dec) – 65,536)/128 where ADC Code uses all 16 bits of the data byte, including the sign bit. Negative Temperature = (ADC Code (dec) – 32,768)/128 where Bit 15 (sign bit) is removed from the ADC code. 13-Bit Temperature Data Format Positive Temperature = ADC Code (dec)/16 Negative Temperature = (ADC Code (dec) − 8192)/16 where ADC Code uses the first 13 MSBs of the data byte, including the sign bit. Negative Temperature = (ADC Code (dec) – 4096)/16 where Bit 15 (sign bit) is removed from the ADC code. 10-Bit Temperature Data Format Positive Temperature = ADC Code (dec)/2 Negative Temperature = (ADC Code (dec) − 1024)/2 where ADC Code uses all 10 bits of the data byte, including the sign bit. Negative Temperature = (ADC Code (dec) − 512)/2 where Bit 9 (sign bit) is removed from the ADC code. 9-Bit Temperature Data Format Positive Temperature = ADC Code (dec) Negative Temperature = ADC Code (dec) − 512 where ADC Code uses all nine bits of the data byte, including the sign bit. Negative Temperature = ADC Code (dec) − 256 where Bit 8 (sign bit) is removed from the ADC code. Rev. 0 | Page 12 of 24 Data Sheet ADT7420 REGISTERS The ADT7420 contains 14 registers: ADDRESS POINTER REGISTER • • • • • • This register is always the first register written to during a write to the ADT7420. It should be set to the address of the register to which the write or read transaction is intended. Table 7 shows the register address of each register on the ADT7420. The default value of the address pointer register is 0x00. Nine temperature registers A status register An ID register A configuration register An address pointer register A software reset Table 7. Address Pointer Register All registers are eight bits wide. The temperature value registers, the status register, and the ID register are read-only. The software reset is a write-only register. On power-up, the address pointer register is loaded with 0x00 and points to the temperature value most significant byte register (Register Address 0x00). Table 6. ADT7420 Registers Register Address 0x00 0x01 0x02 0x03 0x04 0x05 0x06 0x07 0x08 0x09 0x0A 0x0B 0x2F Description Temperature value most significant byte Temperature value least significant byte Status Configuration THIGH setpoint most significant byte THIGH setpoint least significant byte TLOW setpoint most significant byte TLOW setpoint least significant byte TCRIT setpoint most significant byte TCRIT setpoint least significant byte THYST setpoint ID Software reset Power-On Default 0x00 0x00 0x00 0x00 0x20 (64°C) 0x00 (64°C) 0x05 (10°C) 0x00 (10°C) 0x49 (147°C) 0x80 (147°C) 0x05 (5°C) 0xCB 0xXX P7 ADD7 P6 ADD6 P5 ADD5 P4 ADD4 P3 ADD3 P2 ADD2 P1 ADD1 P0 ADD0 TEMPERATURE VALUE REGISTERS The temperature value consists of two bytes, one most significant byte and one least significant byte. These values can be read in two separate 1-byte reads or in a single 2-byte read. For a 2-byte read, only the address of the most significant byte must be loaded into the address pointer register. After the most significant byte is read, the address pointer is auto-incremented so that the least significant byte can read within the same transaction. Bit 0 to Bit 2 are event alarm flags for TLOW, THIGH, and TCRIT. When the ADC is configured to convert the temperature to a 16-bit digital value, then Bit 0 to Bit 2 are no longer used as flag bits and are instead used as the LSBs for the extended digital value. Table 8. Temperature Value MSB Register (Register Address 0x00) Bit [14:8] 15 Default Value 0000000 0 Type R R Name Temp Sign Description Temperature value in twos complement format Sign bit, indicates if the temperature value is negative or positive Table 9. Temperature Value LSB Register (Register Address 0x01) Bit 0 Default Value 0 Type R Name TLOW flag/LSB0 1 0 R THIGH flag/LSB1 2 0 R TCRIT flag/LSB2 [7:3] 00000 R Temp Description Flags a TLOW event if the configuration register, Register Address 0x03[7] = 0 (13-bit resolution). When the temperature value is below TLOW, this bit it set to 1. Contains the Least Significant Bit 0 of the 15-bit temperature value if the configuration register, Register Address 0x03[7] = 1 (16-bit resolution). Flags a THIGH event if the configuration register, Register Address 0x03[7] = 0 (13-bit resolution). When the temperature value is above THIGH, this bit it set to 1. Contains the Least Significant Bit 1 of the 15-bit temperature value if the configuration register, Register Address 0x03[7] = 1 (16-bit resolution). Flags a TCRIT event if the configuration register, Register Address 0x03[7] = 0 (13-bit resolution). When the temperature value exceeds TCRIT, this bit it set to 1. Contains the Least Significant Bit 2 of the 15-bit temperature value if the configuration register, Register Address 0x03[7] = 1 (16-bit resolution). Temperature value in twos complement format. Rev. 0 | Page 13 of 24 ADT7420 Data Sheet STATUS REGISTER CONFIGURATION REGISTER This 8-bit read-only register reflects the status of the overtemperature and undertemperature interrupts that can cause the CT and INT pins to go active. It also reflects the status of a temperature conversion operation. The interrupt flags in this register are reset by a read operation to the status register and/or when the temperature value returns within the temperature limits, including hysteresis. The RDY bit is reset after a read from the temperature value register. In one-shot and 1 SPS modes, the RDY bit is reset after a write to the operation mode bits. This 8-bit read/write register stores various configuration modes for the ADT7420, including shutdown, overtemperature and undertemperature interrupts, one-shot, continuous conversion, interrupt pins polarity, and overtemperature fault queues. Table 10. Status Register (Register Address 0x02) Bit [3:0] 4 Default Value 0000 0 Type R R Name Unused TLOW 5 0 R THIGH 6 0 R TCRIT 7 1 R RDY Description Reads back 0. This bit is set to 1 when the temperature goes below the TLOW temperature limit. The bit clears to 0 when the status register is read and/or when the temperature measured goes back above the limit set in the setpoint TLOW + THYST registers. This bit is set to 1 when the temperature goes above the THIGH temperature limit. The bit clears to 0 when the status register is read and/or when the temperature measured goes back below the limit set in the setpoint THIGH − THYST registers. This bit is set to 1 when the temperature goes above the TCRIT temperature limit. This bit clears to 0 when the status register is read and/or when the temperature measured goes back below the limit set in the setpoint TCRIT − THYST registers. This bit goes low when the temperature conversion result is written into the temperature value register. It is reset to 1 when the temperature value register is read. In one-shot and 1 SPS modes, this bit is reset after a write to the operation mode bits. Table 11. Configuration Register (Register Address 0x03) Bit [1:0] Default Value 00 Type R/W Name Fault queue 2 0 R/W CT pin polarity 3 0 R/W INT pin polarity 4 0 R/W INT/CT mode [6:5] 00 R/W Operation mode 7 0 R/W Resolution Description These two bits set the number of undertemperature/overtemperature faults that can occur before setting the INT and CT pins. This helps to avoid false triggering due to temperature noise. 00 = 1 fault (default). 01 = 2 faults. 10 = 3 faults. 11 = 4 faults. This bit selects the output polarity of the CT pin. 0 = active low. 1 = active high. This bit selects the output polarity of the INT pin. 0 = active low. 1 = active high. This bit selects between comparator mode and interrupt mode. 0 = interrupt mode 1 = comparator mode These two bits set the operational mode for the ADT7420. 00 = continuous conversion (default). When one conversion is finished, the ADT7420 starts another. 01 = one shot. Conversion time is typically 240 ms. 10 = 1 SPS mode. Conversion time is typically 60 ms. This operational mode reduces the average current consumption. 11 = shutdown. All circuitry except interface circuitry is powered down. This bit sets up the resolution of the ADC when converting. 0 = 13-bit resolution. Sign bit + 12 bits gives a temperature resolution of 0.0625°C. 1 = 16-bit resolution. Sign bit + 15 bits gives a temperature resolution of 0.0078°C. Rev. 0 | Page 14 of 24 Data Sheet ADT7420 THIGH SETPOINT REGISTERS The THIGH setpoint MSB and THIGH setpoint LSB registers store the overtemperature limit value. An overtemperature event occurs when the temperature value stored in the temperature value register exceeds the value stored in this register. The INT pin is activated if an overtemperature event occurs. The temperature is stored in twos complement format with the MSB being the temperature sign bit. When reading from this register, the eight most significant bits (Bit 15 to Bit 8) are read first from Register Address 0x04 and then the eight least significant bits (Bit 7 to Bit 0) are read from Register Address 0x05 (THIGH setpoint LSB). Only Register Address 0x04 (THIGH setpoint MSB) needs to be loaded into the address pointer register because the address pointer autoincrements to Register Address 0x05 (THIGH setpoint LSB). The default setting for the THIGH setpoint is 64°C. TLOW SETPOINT REGISTERS The TLOW setpoint MSB and TLOW setpoint LSB registers store the undertemperature limit value. An undertemperature event occurs when the temperature value stored in the temperature value register is less than the value stored in this register. The INT pin is activated if an undertemperature event occurs. The temperature is stored in twos complement format with the MSB being the temperature sign bit. When reading from this register, the eight most significant bits (Bit 15 to Bit 8) are read first from Register Address 0x06 and then the eight least significant bits (Bit 7 to Bit 0) are read from Register Address 0x07. Only Register Address 0x06 (TLOW setpoint MSB) needs to be loaded into the address pointer register because the address pointer auto-increments to Register Address 0x07 (TLOW setpoint LSB). The default setting for the TLOW setpoint is 10°C. TCRIT SETPOINT REGISTERS The TCRIT setpoint MSB and TCRIT setpoint LSB registers store the critical overtemperature limit value. A critical overtemperature event occurs when the temperature value stored in the temperature value register exceeds the value stored in this register. The CT pin is activated if a critical overtemperature event occurs. The temperature is stored in twos complement format with the MSB being the temperature sign bit. When reading from this register, the eight most significant bits (Bit 15 to Bit 8) are read first from Register Address 0x08 (TCRIT setpoint MSB) and then the eight least significant bits (Bit 7 to Bit 0) are read from Register Address 0x09 (TCRIT setpoint LSB). Only Register Address 0x08 (TCRIT setpoint MSB) needs to be loaded into the address pointer register because the address pointer auto-increments to Register Address 0x09 (TCRIT setpoint LSB). The default setting for the TCRIT limit is 147°C. Table 12. THIGH Setpoint MSB Register (Register Address 0x04) Bit Default Value Type Name Description [15:8] 0x20 R/W THIGH MSB MSBs of the overtemperature limit, stored in twos complement format. Table 13. THIGH Setpoint LSB Register (Register Address 0x05) Bit Default Value [7:0] 0x00 Type Name Description R/W THIGH LSB LSBs of the overtemperature limit, stored in twos complement format. Table 14. TLOW Setpoint MSB Register (Register Address 0x06) Bit Default Value Type Name Description [15:8] 0x05 R/W TLOW MSB MSBs of the undertemperature limit, stored in twos complement format. Table 15. TLOW Setpoint LSB Register (Register Address 0x07) Bit Default Value Type Name Description [7:0] 0x00 R/W TLOW LSB LSBs of the undertemperature limit, stored in twos complement format. Table 16. TCRIT Setpoint MSB Register (Register Address 0x08) Bit Default Value Type Name Description [15:8] 0x49 R/W TCRIT MSB MSBs of the critical overtemperature limit, stored in twos complement format. Table 17. TCRIT Setpoint LSB Register (Register Address 0x09) Bit Default Value Type Name Description [7:0] 0x80 R/W TCRIT LSB LSBs of the critical overtemperature limit, stored in twos complement format. Rev. 0 | Page 15 of 24 ADT7420 Data Sheet THYST SETPOINT REGISTER ID REGISTER This 8-bit read/write register stores the temperature hysteresis value for the THIGH, TLOW, and TCRIT temperature limits. The temperature hysteresis value is stored in straight binary format using four LSBs. Increments are possible in steps of 1°C from 0°C to 15°C. The value in this register is subtracted from the THIGH and TCRIT values and added to the TLOW value to implement hysteresis. This 8-bit read-only register stores the manufacture ID in Bit 3 to Bit 7 and the silicon revision in Bit 0 to Bit 2. The default setting for the ID register is 0xCB. Table 18. THYST Setpoint Register (Register Address 0x0A) Bit Default Value Type Name Description [3:0] 0101 R/W THYST Hysteresis value, from 0°C to 15°C. Stored in straight binary format. The default setting is 5°C. [7:4] 0000 R/W N/A Not used. Table 19. ID Register (Register Address 0x0B) Bit [2:0] [7:3] Default Value 011 11001 Type R R Name Revision ID Manufacture ID Description Contains the silicon revision identification number Contains the manufacture identification number Rev. 0 | Page 16 of 24 Data Sheet ADT7420 SERIAL INTERFACE PULL-UP VDD VDD VDD 10kΩ 10kΩ ADT7420 CT INT TO INTERRUPT PIN ON MICROCONTROLLER A0 A1 PULL-UP VDD 10kΩ 10kΩ 0.1µF SCL SDA 09013-014 PULL-UP VDD GND Figure 13. Typical I2C Interface Connection Control of the ADT7420 is carried out via the I2C-compatible serial interface. The ADT7420 is connected to this bus as a slave and is under the control of a master device. 2. Figure 13 shows a typical I2C interface connection. SERIAL BUS ADDRESS Like most I2C-compatible devices, the ADT7420 has a 7-bit serial address. The five MSBs of this address for the ADT7420 are hardwired internally to 10010. Pin A1 and Pin A0 set the two LSBs. These pins can be configured two ways, low and high, to give four different address options. Table 20 shows the different bus address options available. The recommended pull-up resistor value on the SDA and SCL lines is 10 kΩ. Table 20. I2C Bus Address Options A6 1 1 1 1 A5 0 0 0 0 A4 0 0 0 0 Binary A3 1 1 1 1 A2 0 0 0 0 3. 4. A1 0 0 1 1 A0 0 1 0 1 Hex 0x48 0x49 0x4A 0x4B The serial bus protocol operates as follows: 1. The master initiates data transfer by establishing a start condition, defined as a high-to-low transition on the serial data line, SDA, while the serial clock line, SCL, remains high. This indicates that an address/data stream is going to follow. All slave peripherals connected to the serial bus respond to the start condition and shift in the next eight bits, consisting of a 7-bit address (MSB first) plus a read/ write (R/W) bit. The R/W bit determines whether data is written to, or read from, the slave device. The peripheral with the address corresponding to the transmitted address responds by pulling the data line low during the low period before the ninth clock pulse, known as the acknowledge bit. All other devices on the bus then remain idle while the selected device waits for data to be read from or written to it. If the R/W bit is a 0, the master writes to the slave device. If the R/W bit is a 1, the master reads from the slave device. Data is sent over the serial bus in sequences of nine clock pulses, eight bits of data followed by an acknowledge bit from the receiver of data. Transitions on the data line must occur during the low period of the clock signal and remain stable during the high period as a low-to-high transition when the clock is high, which can be interpreted as a stop signal. When all data bytes have been read or written, stop conditions are established. In write mode, the master pulls the data line high during the 10th clock pulse to assert a stop condition. In read mode, the master device pulls the data line high during the low period before the ninth clock pulse. This is known as a no acknowledge. The master takes the data line low during the low period before the 10th clock pulse, then high during the 10th clock pulse to assert a stop condition. It is not possible to mix read and write in one operation because the type of operation is determined at the beginning and cannot subsequently be changed without starting a new operation. Rev. 0 | Page 17 of 24 ADT7420 Data Sheet For the THIGH setpoint, TLOW setpoint, and TCRIT setpoint registers, it is possible to write to both the MSB and the LSB registers in the same write transaction. Writing two bytes of data to these registers requires the serial bus address, the data register address of the MSB register written to the address pointer register, followed by the two data bytes written to the selected data register. This is shown in Figure 15. WRITING DATA It is possible to write either a single byte of data or two bytes to the ADT7420, depending on which registers are to be written. Writing a single byte of data requires the serial bus address, the data register address written to the address pointer register, followed by the data byte written to the selected data register. This is shown in Figure 14. If more than the required number of data bytes is written to a register, the register ignores these extra data bytes. To write to a different register, a start or repeated start is required. 1 9 1 9 SCL 1 SDA 0 0 1 0 A1 A0 P7 R/W START BY MASTER P6 P5 P4 P3 P2 P1 P0 ACK. BY ADT7420 ACK. BY ADT7420 FRAME 1 SERIAL BUS ADDRESS BYTE FRAME 2 ADDRESS POINTER REGISTER BYTE 1 9 SCL (CONTINUED) D7 D6 D5 D4 D3 D2 D1 D0 ACK. BY ADT7420 STOP BY MASTER FRAME 3 DATA BYTE 09013-016 SDA (CONTINUED) Figure 14. Writing to a Register Followed by a Single Byte of Data 1 9 1 9 SCL SDA 1 0 0 1 0 A1 A0 P7 R/W START BY MASTER P6 P5 P4 P3 P2 P1 P0 ACK. BY ADT7420 ACK. BY ADT7420 FRAME 1 SERIAL BUS ADDRESS BYTE FRAME 2 ADDRESS POINTER REGISTER BYTE 1 9 1 9 SCL (CONTINUED) D15 D14 D13 D12 D11 D10 D9 D8 D7 D6 D5 D4 D3 D2 FRAME 4 DATA BYTE FRAME 3 DATA BYTE Figure 15. Writing to a Register Followed by Two Bytes of Data Rev. 0 | Page 18 of 24 D1 D0 ACK. BY ADT7420 ACK. BY ADT7420 STOP BY MASTER 09013-017 SDA (CONTINUED) Data Sheet ADT7420 the register that is going to be read from. In the case of reading back from the 2-byte registers, the address pointer automatically increments from the MSB register address to the LSB register address. READING DATA Reading data from the ADT7420 is done in a single data byte operation for the configuration register, the status register, the THYST setpoint register, and the ID register. A two data byte read operation is needed for the temperature value register, THIGH setpoint register, TLOW setpoint register, and the TCRIT setpoint register. Reading back the contents of an 8-bit register similar to the configuration register is shown in Figure 16. Reading back the contents of the temperature value register is shown in Figure 17. To read from another register, execute another write to the address pointer register to set up the relevant register address. Thus, block reads are not possible, that is, there is no I2C address pointer auto-increment except when reading back from a 16-bit register. If the address pointer register has previously been set up with the address of the register that is going to receive a read command, there is no need to repeat a write operation to set up the register address again. Reading back from any register first requires a single-byte write operation to the address pointer register to set up the address of 9 1 1 9 SCL 1 SDA 0 0 0 1 A1 A0 R/W P7 P6 P5 P4 P3 P2 P1 P0 ACK. BY ADT7420 START BY MASTER ACK. BY ADT7420 FRAME 2 ADDRESS POINTER REGISTER BYTE FRAME 1 SERIAL BUS ADDRESS BYTE 9 1 1 9 SCL 0 0 1 0 A1 A0 R/W D7 D6 ACK. BY ADT7420 FRAME 3 SERIAL BUS ADDRESS BYTE D5 D4 D3 D2 D1 FRAME 4 DATA BYTE FROM CONFIGURATION REGISTER D0 NO ACK. BY STOP BY MASTER MASTER 09013-018 1 SDA REPEAT START BY MASTER Figure 16. Reading Back Data from the Configuration Register 9 1 9 1 SCL SDA 1 0 START 0 0 1 A1 A0 ADT7410 DEVICE ADDRESS ACK. BY ADT7420 1 SR A7 R/W A6 A1 A0 ACK. BY ADT7420 REGISTER ADDRESS[A7:A0] 9 1 9 SCL 1 REPEAT START 0 A1 A0 ADT7410 DEVICE ADDRESS R/W ACK. BY ADT7420 D7 D6 D1 TEMPERATURE VALUE REGISTER MSB DATA D0 D7 ACK. BY MASTER D6 D1 TEMPERATURE VALUE REGISTER LSB DATA D0 NO ACK. BY MASTER NOTES 1. A START CONDITION AT THE BEGINNING IS DEFINED AS A HIGH-TO-LOW TRANSITION ON SDA WHILE SCL REMAINS HIGH. 2. A STOP CONDITION AT THE END IS DEFINED AS A LOW-TO-HIGH TRANSITION ON SDA WHILE SCL REMAINS HIGH. 3. THE MASTER GENERATES THE NO ACKNOWLEDGE AT THE END OF THE READBACK TO SIGNAL THAT IT DOES NOT WANT ADDITIONAL DATA. 4. TEMPERATURE VALUE REGISTER MSB DATA AND TEMPERATURE VALIUE REGISTER LSB DATA ARE ALWAYS SEPARATED BY A LOW ACK BIT. 5. THE R/W BIT IS SET TO A1 TO INDICATE A READBACK OPERATION. Figure 17. Reading Back Data from the Temperature Value Register Rev. 0 | Page 19 of 24 09013-023 SDA ADT7420 Data Sheet RESET GENERAL CALL To reset the ADT7420 without having to reset the entire I C bus, an explicit reset command is provided. This uses a particular address pointer word as a command word to reset the part and upload all default settings. The ADT7420 does not respond to (does not acknowledge) I2C bus commands while the default values upload for approximately 200 µs. Use the following sequence to perform a reset: 2 1. 2. 3. 4. 5. 6. Write to the ADT7420 using the appropriate address. Get acknowledge. Set the register address to 0x2F. Get acknowledge. Apply stop condition. Wait 200 µs for the part to reset its registers to the default power-up settings. When a master issues a slave address consisting of seven 0s with the eighth bit (R/W bit) set to 0, this is known as the general call address. The general call address is for addressing every device connected to the I2C bus. The ADT7420 acknowledges this address and reads in the following data byte. If the second byte is 0x06, the ADT7420 is reset, completely uploading all default values. The ADT7420 does not respond to the I2C bus commands (do not acknowledge) while the default values upload for approximately 200 µs. The ADT7420 does not acknowledge any other general call commands. Rev. 0 | Page 20 of 24 Data Sheet ADT7420 INT AND CT OUTPUTS Comparator Mode The INT and CT pins are open-drain outputs, and both pins require a 10 kΩ pull-up resistor to VDD. The ADT7420 must be fully powered up to VDD before reading INT and CT data. In comparator mode, the INT pin returns to its inactive status when the temperature drops below the THIGH − THYST limit or rises above the TLOW + THYST limit. UNDERTEMPERATURE AND OVERTEMPERATURE DETECTION Putting the ADT7420 into shutdown mode does not reset the INT state in comparator mode. The INT and CT pins have two undertemperature/overtemperature modes: comparator mode and interrupt mode. The interrupt mode is the default power-up overtemperature mode. The INT output pin becomes active when the temperature is greater than the temperature stored in the THIGH setpoint register or less than the temperature stored in the TLOW setpoint register. How this pin reacts after this event depends on the overtemperature mode selected. Interrupt Mode In interrupt mode, the INT pin goes inactive when any ADT7420 register is read. Once the INT pin is reset, it goes active again only when the temperature is greater than the temperature stored in the THIGH setpoint register or less than the temperature stored in the TLOW setpoint register. Placing the ADT7420 into shutdown mode resets the INT pin in the interrupt mode. Figure 18 illustrates the comparator and interrupt modes for events exceeding the THIGH limit with both pin polarity settings. Figure 19 illustrates the comparator and interrupt modes for events exceeding the TLOW limit with both pin polarity settings. TEMPERATURE 82°C 81°C THIGH 80°C 79°C 78°C 77°C 76°C THIGH – THYST 75°C 74°C 73°C INT PIN (COMPARATOR MODE) POLARITY = ACTIVE LOW INT PIN (INTERRUPT MODE) POLARITY = ACTIVE LOW INT PIN (COMPARATOR MODE) POLARITY = ACTIVE HIGH TIME READ READ READ 09013-020 INT PIN (INTERRUPT MODE) POLARITY = ACTIVE HIGH Figure 18. INT Output Temperature Response Diagram for THIGH Overtemperature Events Rev. 0 | Page 21 of 24 ADT7420 Data Sheet TEMPERATURE –13°C –14°C TLOW + THYST –15°C –16°C –17°C –18°C –19°C TLOW –20°C –21°C –22°C INT PIN (COMPARATOR MODE) POLARITY = ACTIVE LOW INT PIN (INTERRUPT MODE) POLARITY = ACTIVE LOW INT PIN (COMPARATOR MODE) POLARITY = ACTIVE HIGH TIME READ READ READ 09013-021 INT PIN (INTERRUPT MODE) POLARITY = ACTIVE HIGH Figure 19. INT Output Temperature Response Diagram for TLOW Undertemperature Events Rev. 0 | Page 22 of 24 Data Sheet ADT7420 APPLICATIONS INFORMATION THERMAL RESPONSE TIME POWERING FROM A SWITCHING REGULATOR Thermal response is a function of the thermal mass of the temperature sensor, but it is also heavily influenced by the mass of the object the IC is mounted to. For example, a large PCB containing large amounts of copper tracking can act as a large heat sink and slow the thermal response. For a faster thermal response, it is recommended to mount the sensor on as small a PCB as possible. Precision analog devices, such as the ADT7420 require a wellfiltered power source. If the ADT7420 is powered from a switching regulator, noise may be generated above 50 kHz that may affect the temperature accuracy specifications. To prevent this, an RC filter should be used between the power supply and ADT7420 VDD. The value of the components used should be carefully considered to ensure that the peak value of the supply noise is less than 1 mV. The RC filter should be mounted as far away as possible from the ADT7420 to ensure that the thermal mass is kept as low as possible. Figure 10 shows the typical response time of less than two seconds to reach 63.2% of its temperature span. The temperature value is read back as a 16-bit value through the digital interface. The response time includes all delays incurred on chip during signal processing. TEMPERATURE MEASUREMENT SUPPLY DECOUPLING The ADT7420 must have a decoupling capacitor connected between VDD and GND; otherwise, incorrect temperature readings will be obtained. A 0.1 µF decoupling capacitor such as a high frequency ceramic type must be used and mounted as close as possible to the VDD pin of the ADT7420. If possible, the ADT7420 should be powered directly from the system power supply. This arrangement, shown in Figure 20, isolates the analog section from the logic-switching transients. Even if a separate power supply trace is not available, generous supply bypassing reduces supply-line induced errors. Local supply bypassing consisting of a 0.1 µF ceramic capacitor is critical for the temperature accuracy specifications to be achieved. 0.1µF For air or surface temperature measurements, take care to isolate the package, leads, and exposed pad from ambient air temperature. Use of a thermally conductive adhesive can help to achieve a more accurate surface temperature measurement. QUICK GUIDE TO MEASURING TEMPERATURE The following is a quick guide for measuring temperature in continuous conversion mode (default power-up mode). Execute each step sequentially. ADT7420 POWER SUPPLY 1. After powering up the ADT7420, verify the setup by reading the device ID (Register Address 0x0B). It should read 0xCB. 2. After consistent consecutive readings are obtained from Step 1, proceed to read the configuration register (0x03), TCRIT (0x08, 0x09), THIGH (0x04, 0x05), and TLOW (0x06, 0x07) registers. Compare to the specified defaults in Table 6. If all the readings match, the interface is operational. 3. Write to the configuration register to set the ADT7420 to the desired configuration. 4. Read the temperature value MSB register, followed by the temperature value LSB register. Both registers should produce a valid temperature measurement. 09013-022 TTL/CMOS LOGIC CIRCUITS The ADT7420 accurately measures and converts the temperature at the surface of its own semiconductor chip. Thermal paths run through the leads, the exposed pad, as well as the plastic package. When the ADT7420 is used to measure the temperature of a nearby heat source, the thermal impedance between the heat source and the ADT7420 must be considered because this impacts the accuracy and thermal response of the measurement. Figure 20. Use of Separate Traces to Reduce Power Supply Noise Rev. 0 | Page 23 of 24 ADT7420 Data Sheet OUTLINE DIMENSIONS PIN 1 INDICATOR 4.10 4.00 SQ 3.90 0.35 0.30 0.25 0.65 BSC 16 13 PIN 1 INDICATOR 12 1 EXPOSED PAD 4 2.70 2.60 SQ 2.50 9 0.80 0.75 0.70 0.25 MIN BOTTOM VIEW 0.05 MAX 0.02 NOM COPLANARITY 0.08 0.20 REF SEATING PLANE 5 FOR PROPER CONNECTION OF THE EXPOSED PAD, REFER TO THE PIN CONFIGURATION AND FUNCTION DESCRIPTIONS SECTION OF THIS DATA SHEET. COMPLIANT TO JEDEC STANDARDS MO-220-WGGC. 012909-B 0.45 0.40 0.35 TOP VIEW 8 Figure 21. 16-Lead Lead Frame Chip Scale Package [LFCSP_WQ] 4 mm × 4 mm Body, Very Thin Quad (CP-16-17) Dimensions shown in millimeters ORDERING GUIDE Model1 ADT7420UCPZ-R2 ADT7420UCPZ-RL7 EVAL-ADT7X20EBZ 1 Operating Temperature Range −40°C to +150°C −40°C to +150°C Package Description 16-lead LFCSP_WQ 16-lead LFCSP_WQ Evaluation Board Z = RoHS Compliant Part. I2C refers to a communications protocol originally developed by Philips Semiconductors (now NXP Semiconductors). ©2012 Analog Devices, Inc. All rights reserved. Trademarks and registered trademarks are the property of their respective owners. D09013-0-12/12(0) Rev. 0 | Page 24 of 24 Package Option CP-16-17 CP-16-17