LTC2995 Temperature Sensor and Dual Voltage Monitor with Alert Outputs DESCRIPTION FEATURES n n n n n n n n n n n n n Monitors Temperature and Two Voltages Voltage Output Proportional to Temperature Adjustable Thresholds for Temperature and Voltage ±1°C Remote Temperature Accuracy ±2°C Internal Temperature Accuracy ±1.5% Voltage Threshold Accuracy 3.5ms Update Time 2.25V to 5.5V Supply Voltage Input Glitch Rejection Adjustable Reset Timeout 220μA Quiescent Current Open Drain Alert Outputs Available in 3mm × 3mm QFN Package APPLICATIONS n n n n The LTC®2995 is a high accuracy temperature sensor and dual supply monitor. It converts the temperature of an external diode sensor and/or its own die temperature to an analog output voltage while rejecting errors due to noise and series resistance. Two supply voltages and the measured temperature are compared against upper and lower limits set with resistive dividers. If a threshold is exceeded, the device communicates an alert by pulling low the correspondent open drain logic output. The LTC2995 gives ±1°C accurate temperature results using commonly available NPN or PNP transistors or temperature diodes built into modern digital devices. Voltages are monitored with 1.5% accuracy. A 1.8V reference output simplifies threshold programming and can be used as an ADC reference input. The LTC2995 provides an accurate, low power solution for temperature and voltage monitoring in a compact 3mm × 3mm QFN package. Network Servers Core, I/O Voltage Monitors Desktop and Notebook Computers Environmental Monitoring 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. TYPICAL APPLICATION Dual OV/UV Supply and Single OT/UT Remote Temperature Monitor VPTAT vs Remote Diode Temperature 2.5V 1.8 ASIC 1.2V 1.6 0.1μF PS 470pF 194k TEMPERATURE SENSOR D– DS VH1 LTC2995 VPTAT (V) D+ VCC 1.4 1.2 10.2k VL1 45.3k VPTAT 64.4k TO2 VH2 TO1 10.2k VL2 45.3k VREF 20k VT2 VT1 20k 4mV/K OT T > 125°C UT T < 75°C OV +10% UV –10% 1.0 SYSTEM MONITOR 0.8 25 50 75 100 125 150 –50 –25 0 REMOTE DIODE TEMPERATURE (°C) 2995 TA01b GND TMR 140k 5nF 2995 TA01a 2995f 1 LTC2995 ABSOLUTE MAXIMUM RATINGS PIN CONFIGURATION (Notes 1, 2) VCC .............................................................. –0.3V to 6V TMR, D+, D–, DS, PS, VPTAT, VREF........ –0.3V to VCC + 0.3V UV, OV, TO1, T02 .......................................... –0.3V to 6V VH1, VL1, VH2, VL2, VT1, VT2 ..................... –0.3V to 6V Operating Ambient Temperature Range LTC2995C ................................................ 0°C to 70°C LTC2995I .............................................–40°C to 85°C LTC 2995H ......................................... –40°C to 125°C Storage Temperature Range .................. –65°C to 150°C TMR GND DS PS VH1 TOP VIEW 20 19 18 17 16 15 UV VL1 1 14 OV VH2 2 13 TO2 21 VL2 3 12 T01 VT2 4 11 VREF 7 8 9 10 D– VPTAT VCC GND 6 D+ VT1 5 UD PACKAGE 20-LEAD (3mm × 3mm) PLASTIC QFN TJMAX = 150°C, θJA = 59°C/W EXPOSED PAD PCB GROUND CONNECTED OPTIONAL ORDER INFORMATION LEAD FREE FINISH TAPE AND REEL PART MARKING* PACKAGE DESCRIPTION TEMPERATURE RANGE LTC2995CUD#PBF LTC2995CUD#TRPBF LFQV 20-Lead (3mm × 3mm) Plastic QFN 0°C to 70°C LTC2995IUD#PBF LTC2995IUD#TRPBF LFQV 20-Lead (3mm × 3mm) Plastic QFN –40°C to 85°C LTC2995HUD#PBF LTC2995HUD#TRPBF LFQV –40°C to 125°C 20-Lead (3mm × 3mm) Plastic QFN 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/ For more information on tape and reel specifications, go to: http://www.linear.com/tapeandreel/ ELECTRICAL CHARACTERISTICS The l denotes the specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25°C, VCC = 3.3V, unless otherwise noted. SYMBOL PARAMETER VCC Supply Voltage UVLO Supply Undervoltage Lockout Threshold ICC Average Supply Current CONDITIONS VCC Falling MIN l 2.25 l 1.7 l TYP MAX UNITS 5.5 V 1.9 2.1 V 220 300 μA 1.8 1.8 1.8 1.8 1.803 1.804 1.807 1.808 V V V V ±1.5 mV –192 μA Temperature Measurement VREF Reference Voltage LTC2995 LTC2995C LTC2995I LTC2995H l l l VREF Load Regulation ILOAD = ±200μA l Remote Diode Sense Current 1.797 1.793 1.790 1.787 –8 2995f 2 LTC2995 ELECTRICAL CHARACTERISTICS The l denotes the specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25°C, VCC = 3.3V, unless otherwise noted. SYMBOL PARAMETER Tconv Temperature Update Interval KT VPTAT Slope Ideality Factor η = 1.004 VPTAT Load Regulation ILOAD = ±200μA Tint TRMT CONDITIONS MIN l Temperature Error vs Supply TRS Series Resistance Cancellation Error 5 UNITS ms mV/K ±1.5 mV ±0.5 ±2 ±1 TAMB = –40°C to 125°C °C °C 0°C to 85°C (Notes 3, 4) –40°C to 0°C (Notes 3, 4) 85°C to 125°C (Notes 3, 4) ±0.25 ±0.25 ±0.25 ±1 ±1.5 ±1.5 °C °C °C Temperature Noise TVCC MAX 3.5 4 Internal Temperature Accuracy Remote Temperature Error, η = 1.004 TYP 0.15 0.01 l ±0.5 l RSERIES = 100Ω °CRMS °CRMS/√Hz °C/V ±0.25 ±1 °C Temperature and Voltage Monitoring VUOT Undervoltage/Overvoltage Threshold l 492 500 508 mV TOFF VT1, VT2 Offset l –3 –1 1 °C ΔTHYST VT1, VT2 Temperature Hysteresis l 2 5 10 °C tUOD UV, OV 0.5 2 ms IIN VH1, VL1, VH2, VL2, VT1, VT2, Input Current tUOTO UV/OV Time-Out-Period ITMR Input 5mV Above/Below Threshold l l CTMR = TMR Open CTMR = 1nF l 5 l TMR Current 0.5 10 ±20 nA 20 ms ms ±2.5 μA Three State Pins DS, PS VDS,PS(H,TH) PS, DS Input High Threshold l VCC – 0.4 VCC – 0.1 V VDS,PS(H,TL) PS, DS Input Low Threshold l 0.1 0.4 V l ±4 μA l ±1 μA IDS,PS(IN,HL) PS, DS High, Low Input Current IDS,PS(IN,Z) DS, PS at 0V or VCC Allowable Leakage Current Digital Outputs VOH High Level Output Voltage, TO1, TO2, UV, OV I = –0.5μA l VOL Low Level Output Voltage, TO1, TO2, UV, OV I = 3mA l 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 currents into pins are positive; all voltages are referenced to GND unless otherwise noted. VCC – 1.2 V 0.4 V Note 3: Remote diode temperature, not LTC2995 temperature. Note 4: Guaranteed by design and test correlation. 2995f 3 LTC2995 TIMING DIAGRAMS VLn Monitor Timing VHn Monitor Timing VHn VUOT VLn tUOD UV VUOT tUOTO tUOD OV 1V tUOTO 1V 2995 TD01 VHn Monitor Timing (TMR Pin Strapped to VCC) VHn VUOT VLn Monitor Timing (TMR Pin Strapped to VCC) VLn tUOD UV 2995 TD02 VUOT tUOD tUOD OV 1V 2995 TD03 tUOD 1V 2995 TD04 2995f 4 LTC2995 TYPICAL PERFORMANCE CHARACTERISTICS Remote Temperature Error vs Ambient Temperature Temperature Error with LTC2995 at Same Temperature as Remote Diode 3 TINTERNAL = TREMOTE TRMT ERROR (°C) TRMT ERROR (°C) 2 1 0 –1 –2 Internal Temperature Error vs Ambient Temperature 3 TREMOTE = 25°C 2 2 1 1 TINT ERROR (°C) 3 TA = 25°C, VCC = 3.3V unless otherwise noted. 0 –1 –2 –3 –50 –25 0 25 50 75 TA (°C) 0 25 50 75 TA (°C) 0.4 4 4 0.2 2 2 ERROR (°C) 6 ERROR (°C) 6 0 –2 –2 –0.4 –4 –4 3 4 VCC (V) –6 6 5 100 125 150 0 –0.2 2 50 75 TA (°C) Remote Temperature Error vs CDECOUPLE (Between D+ and D–) 0.6 –0.6 25 2995 G03 Remote Temperature Error vs Series Resistance 0 0 2995 G02 Temperature Error vs Supply Voltage ERROR (°C) –3 –50 –25 100 125 150 2995 G01 0 200 400 600 800 1000 SERIES RESISTANCE (Ω) 2995 G04 –6 1200 0 6 8 2 4 DECOUPLE CAPACITOR (nF) 2995 G05 0.20 10 2995 G06 UVLO vs Temperature VCC Rising, Falling VPTAT Noise vs Averaging Time Buffered Reference Voltage vs Temperature 2.2 1.810 VCC RISING VCC FALLING 0.15 1.805 2.0 0.10 VREF (V) UVLO (V) VPTAT NOISE (°C RMS) –1 –2 –3 –50 –25 100 125 150 0 1.800 1.8 0.05 0 0.01 1.795 0.1 10 100 1 AVERAGING TIME (ms) 1000 2995 G07 1.6 –50 –25 0 25 50 75 TA (°C) 100 125 150 2995 G08 1.790 –50 –25 0 25 50 75 TA (°C) 100 125 150 2995 G09 2995f 5 LTC2995 TYPICAL PERFORMANCE CHARACTERISTICS Load Regulation of VREF – Voltage vs Current 1.80 10 VCC = 2.25V VCC = 3.5V VCC = 4.5V VCC = 5.5V 1.20 VPTAT (V) VREF (V) 1.22 VCC = 2.25V VCC = 3.5V VCC = 4.5V VCC = 5.5V 1.81 Single Wire Remote Temperature Error vs Ground Noise Load Regulation of VPTAT – Voltage vs Current ABSOLUTE TEMPERATURE ERROR (°C) 1.82 TA = 25°C, VCC = 3.3V unless otherwise noted. 1.18 1.16 1.79 1.78 1.14 –4 –2 2 0 LOAD CURRENT (mA) 4 –4 2 –2 0 LOAD CURRENT (mA) 0.1 100 10 FREQUENCY (kHz) 1000 2995 G12 UV, OV, TO1, TO2 vs Output Sink Current 1 1200 1000 VUV/OV/TO1/TO2 (V) 0.8 800 600 400 0.6 0.4 0.2 200 0 1 10 OVERDRIVE (mV) 0 100 0 5 10 15 20 I (mA) Reset Timeout Period vs Capacitance 30 35 Supply Current vs Temperature 10000 250 240 SUPPLY CURRENT (μA) 1000 100 10 1 0.1 25 2995 G14 2995 G13 RESET TIMEOUT tUOTO (ms) 1 2995 G11 Delay vs Comparator Overdrive DELAY (μs) 1 0.01 0.1 4 2995 G10 VAC = 50mVP-P 230 220 210 1 10 100 TMR PIN CAPACITANCE (nF) 1000 2995 G15 200 –50 –25 0 25 50 75 TA (°C) 100 125 150 2995 G16 2995f 6 LTC2995 PIN FUNCTIONS D+: Diode Sense Current Source. D+ sources the remote diode sensing current. Connect D+ to the anode of the remote sensor device. It is recommended to connect a 470pF bypass capacitor between D+ and D –. Larger capacitors may cause settling time errors (see Typical Performance Characteristics). If D+ is tied to VCC, the LTC2995 measures the internal sensor temperature. Tie D+ to VCC if unused. D –: Diode Sense Current Sink. Connect D – to the cathode of the remote sensor device. Tie D – to GND for single wire remote temperature measurement (see Applications Information) or internal temperature sensing. DS: Diode Select Input. Three state pin that selects temperature sensor location. Tie DS to VCC to monitor the temperature of the internal diode or to GND to monitor the temperature of the external diode. When DS is left unconnected, the LTC2995 monitors both sensors alternately. If D+ is tied to VCC, the LTC2995 measures the internal sensor temperature regardless of the state of DS. Exposed Pad: Exposed pad may be left open or soldered to GND for better thermal coupling. GND: Device Ground OV: Overvoltage Logic Output. Open drain logic output that pulls to GND when either the voltage at VL1 or VL2 is above 0.5V. Held low for a programmable delay time set by the capacitor connected to pin TMR. OV has a weak 400kΩ pull-up to VCC and may be pulled above VCC using an external pull-up. Leave OV open if unused. PS: Polarity Select Input. Selects the polarity of temperature thresholds VT1 and VT2. Connect PS to VCC to configure VT1 as undertemperature and VT2 as overtemperature threshold. Leave PS unconnected to configure both VT1 and VT2 as overtemperature thresholds. Connect PS to GND to configure both VT1 and VT2 as undertemperature thresholds. Tie to VCC if temperature thresholds are unused. TMR: Reset Delay Timer. Attach an external capacitor (CTMR) to GND to set the delay time until alerts on TO1, TO2, UV and OV are reset. Leaving the pin open generates a minimum delay of 500μs. Capacitance on this pin adds an additional 8ms/nF reset delay time. Tie TMR to VCC to bypass the timer. TO1: Temperature Logic Output 1. Open drain logic output that pulls to GND when VPTAT crosses the threshold voltage on pin VT1 with a polarity set by the PS pin (see Table 3 in Applications Information). When VPTAT crosses the threshold voltage on pin VT1 with opposite polarity, an additional hysteresis of 20mV is required to release TO1 high after a delay adjustable by the capacitor on TMR. TO1 has a weak 400kΩ pull-up to VCC and may be pulled above VCC using an external pull-up. Leave TO1 open if unused. TO2: Temperature Logic Output 2. Open drain logic output that pulls to GND when VPTAT crosses the threshold voltage on pin VT2 with a polarity set by the PS pin (see Table 3 in Applications Information). When VPTAT crosses the threshold voltage on pin VT2 with opposite polarity, an additional hysteresis of 20mV is required to release TO2 high after a delay adjustable by the capacitor on TMR. TO2 has a weak 400kΩ pull-up to VCC and may be pulled above VCC using an external pull-up. Leave TO2 open if unused. UV: Undervoltage Logic Output. Open drain logic output that pulls to GND when either the voltage at VH1 or VH2 is below 0.5V. Held low for an adjustable delay time set by the capacitor connected to pin TMR. UV has a weak 400kΩ pull-up to VCC and may be pulled above VCC using an external pull-up. Leave pin open if unused. VCC: Supply Voltage. Bypass this pin to GND with a 0.1μF (or greater) capacitor. VCC operating range is 2.25V to 5.5V. VH1, VH2: Voltage High Inputs 1 and 2. When the voltage on either pin is below 0.5V, an undervoltage condition is triggered. Tie pin to VCC if unused. VL1, VL2: Voltage Low Inputs 1 and 2. When the voltage on either pin is above 0.5V, an overvoltage condition is triggered. Tie pin to GND if unused. VPTAT: Proportional to Absolute Temperature Voltage Output. The voltage on this pin is proportional to the selected sensor’s absolute temperature. An internal or external sensor is chosen with the DS pin. VPTAT can drive up to ±200μA of load current and up to 1000pF of capacitive load. For larger load capacitances insert a 1k 2995f 7 LTC2995 PIN FUNCTIONS resistor between VPTAT and the load to ensure stability. VPTAT is pulled low when the supply voltage goes below the under voltage lockout threshold. VT1: Temperature Threshold 1. When VPTAT crosses the voltage on VT1 with a polarity set by the PS pin, TO1 is pulled low. Tie VT1 to GND if unused. VREF: Voltage Reference Output. VREF provides a 1.8V reference voltage. VREF can drive up to ±200μA of load current and up to 1000pF of capacitive load. For larger load capacitances insert 1kΩ between VREF and the load to ensure stability. Leave VREF open if unused. VT2: Temperature Threshold 2. When VPTAT crosses the voltage on VT2 with a polarity set by the PS pin, TO2 is pulled low. Tie VT2 to VCC if unused. BLOCK DIAGRAM 16 9 TMR VCC VCC 400k 20 – VH1 CH1 UV + – 15 UV PULSE GENERATOR CL1 OSCILLATOR 1 2 VL1 + – VH2 + 2V – VCC UVLO CH2 VCC 400k + – OV CL2 200kΩ 3 VL2 + + 11 14 OV PULSE GENERATOR VREF 1.2V 1.8V 1.3MΩ 200k – 0.5V VCC 500k 400k 4 VT2 – 400k TO2 CT2 + UVLO – VCC 400k CT1 TO1 5 8 VT1 VPTAT 13 TO1/TO2 PULSE GENERATOR + 3 STATE DECODE T TO V CONVERTER 1 12 3 STATE DECODE 18 DS 7 D– 6 D+ 19 PS 17 GND 2995 BD 8 2995f LTC2995 OPERATION Overview The LTC2995 combines the functionality of a temperature measurement and monitor device with a dual voltage supervisor. It provides a buffered voltage proportional to the absolute temperature of either an internal or a remote diode (VPTAT) and compares this voltage to thresholds that can be set by external resistor dividers from the on-board reference (VREF). The LTC2995 also provides four voltage threshold inputs that are continuously compared to an internal 0.5V reference allowing two systems voltages to be monitored for undervoltage and overvoltage conditions. Diode Temperature Sensor Temperature measurements are conducted by measuring the voltage of either an internal or an external diode with multiple test currents. The relationship between diode voltage VD and diode current ID can be solved for absolute Temperature in degrees Kelvin T: T= q VD t η t k ln ⎛ ID⎞ ⎜⎝ I ⎟⎠ S where IS is a process dependent factor on the order of 10 –13A, η is the diode ideality factor, k is the Boltzmann constant and q is the electron charge. This equation shows a relationship between temperature and voltage dependent on the process depended variable IS. Measuring the same diode (with the same value IS) at two different currents (ID1 and ID2) yields an expression independent of IS: T= q V – VD1 t D2 η tk ⎛ ID2 ⎞ ln ⎜ ⎟ ⎝ ID1⎠ Series Resistance Cancellation Resistance in series with the remote diode causes a positive temperature error by increasing the measured voltage at each test current. The composite voltage equals: VD + VERROR = η kT ⎛I ⎞ t ln ⎜ D⎟ + RS t ID ⎝ I S⎠ q The LTC2995 removes this error term from the sensor signal by subtracting a cancellation voltage VCANCEL. A resistance extraction circuit uses one additional current measurement to determine the series resistance in the measurement path. Once the correct value of the resistor is determined, VCANCEL equals VERROR. Now the temperature to voltage converter input signal is free from errors due to series resistance. LTC2995 can cancel series resistances up several hundred ohms (see Typical Performance Characteristics curves). Higher series resistances cause the cancelation voltage to saturate. 2995f 9 LTC2995 APPLICATIONS INFORMATION Temperature Measurements Choosing an External Sensor The LTC2995 continuously measures the sensor diode at different test currents and generates a voltage proportional to the absolute temperature of the sensor at the VPTAT pin. The voltage at VPTAT is updated every 3.5ms. The LTC2995 is factory calibrated for an ideality factor of 1.004, which is typical of the popular MMBT3904 NPN transistor. Semiconductor purity and wafer level processing intrinsically limit device-to-device variation, making these devices interchangeable between manufacturers with a temperature error of typically less than 0.5°C. Some recommended sources are listed in Table 2: The gain of VPTAT is calibrated to 4mV/K for the measurement of the internal diode as well as for remote diodes with an ideality factor of 1.004. TKELVIN V = PTAT 4mV/K Table 2 Recommended Transistors for Use As Temperature Sensors (η = 1.004) MANUFACTURER If an external sensor with an ideality factor different from 1.004 is used, the gain of VPTAT will be scaled by the ratio of the actual ideality factor (ηACT) to 1.004. In these cases, the temperature of the external sensor can be calculated from VPAT by: TKELVIN V 1.004 = PTAT • 4mV/K ηACT PART NUMBER PACKAGE Fairchild Semiconductor MMBT3904 SOT-23 Central Semiconductor CMBT3904 SOT-23 Diodes Inc. MMBT3904 SOT-23 MMBT3904LT1 SOT-23 NXP MMBT3904 SOT-23 Infineon MMBT3904 SOT-23 UMT3904 SC-70 On Semiconductor Rohm Temperature in degrees Celsius can be deduced from degrees Kelvin by: TCELSIUS = TKELVIN – 273.15 The three-state diode select pin (DS) determines whether the temperature of the external or the internal diode is measured and displayed at VPTAT as described in Table 1. Discrete two terminal diodes are not recommended as remote sensing devices as their ideality factor is typically much higher than 1.004. Also MOS transistors are not suitable as they don’t exhibit the required current to temperature relationship. Furthermore gold doped transistors (low beta), high frequency and high voltage transistors should be avoided as remote sensing devices. Connecting an External Sensor Table 1. Diode Selection DIODE LOCATION DS PIN Internal VCC External GND Both Open If the DS pin is left open, the LTC2995 measures both diodes alternately and VPTAT changes every 30ms from the voltage corresponding to the temperature of the internal sensor to the voltage corresponding to the temperature of the external sensor. If D+ is tied to VCC, the LTC2995 measures the internal diode regardless of the state of the DS pin. The change in sensor voltage per °C is hundreds of microvolts, so electrical noise must be kept to a minimum. Bypass D+ and D – with a 470pF capacitor close to the LTC2995 to suppress external noise. Recommended shielding and PCB trace considerations for best noise immunity are illustrated in Figure 1. GND SHIELD TRACE 470pF D+ D– LTC2995 GND NPN SENSOR 2995 F01 Figure 1. Recommended PCB Layout 2995f 10 LTC2995 APPLICATIONS INFORMATION Leakage currents at D+ affect the precision of the remote temperature measurements. 100nA leakage current leads to an additional error of 2°C (see Typical Performance Characteristics). components. Noise around odd multiples of 6kHz (±20%)is amplified by the measurement algorithm and converted at a DC offset in the temperature measurement (see Typical Performance Characteristics). Note that bypass capacitors greater than 1nF will cause settling time errors in the different measurement currents and therefore introduce an error in the temperature measurement (see Typical Performance Characteristics). The LTC2995 can withstand up to ±4kV of electrostatic discharge (ESD, human body). ESD beyond this voltage can damage or degrade the device including lowering the remote sensor measurement accuracy due to increased leakage currents on D+ or D –. The LTC2995 compensates series resistance in the measurement path and thereby allows accurate remote temperature measurements even with several meters of distance between the sensor and the device. The cable length between the sensor and the LTC2995 is only limited by the mutual capacitance introduced between D+ and D – which degrades measurement accuracy (see Typical Performance Characteristics). For example an AT6 cable with 50pF/m should be kept shorter than ~20m to keep the capacitance less than 1nF. To save wiring, the cathode of the remote sensor can also be connected to remote GND and D – to local GND as shown below. D+ 2N3904 LTC2995 470pF D– GND 2995 F02 Figure 2. Single Wire Remote Temperature Sensing The temperature measurement of the LTC2995 relies only on differences between the diode voltage at multiple test circuits. Therefore DC offsets smaller than 300mV between remote and local GND do not impact the precision of the temperature measurement. The cathode of the sensor can accommodate modest ground shifts across a system which is beneficial in applications where a good thermal connectivity of the sensor to a device whose temperature is to be monitored (shunt resistor, coil, etc.) is required. Care must be taken if the potential difference between the cathode and D – does not only content DC but also AC To protect the sensing inputs against larger ESD strikes, external protection can be added using TVS diodes to ground (Figure 3). Care must be taken to choose diodes with low capacitance and low leakage currents in order not to degrade the external sensor measurement accuracy (see Typical Performance Characteristics curves). 10Ω D+ MMBT3904 LTC2995 220pF 10Ω D– GND 2995 F03 PESD5Z6.0 Figure 3. Increasing ESD Robustness with TVS Diodes To make the connection of the cable to the IC polarity insensitive during installation, two sensor transistors with opposite polarity at the end of a two wire cable can be used as shown on Figure 4. D+ MMBT3904 LTC2995 470pF D– GND 2995 F04 Figure 4. Polarity Insensitive Remote Diode Sensor Again, care must be taken that the leakage current of the second transistor does not degrade the measurement accuracy. 2995f 11 LTC2995 APPLICATIONS INFORMATION Output Noise Filtering The VPTAT output typically exhibits 0.6mV RMS (0.25°C RMS) noise. For applications which require lower noise digital or analog averaging can be applied to the output. Choose the averaging time according to: t AVG 2 ⎛ [°C Hz ]⎞ 0.01 ⎟ =⎜ ⎠ ⎝ TNOISE where t AVG is the averaging time and TNOISE the desired temperature noise in °C RMS. For example, if the desired noise performance is 0.015°C RMS, set the averaging time to one second. See Typical Performance Characteristics. Temperature Monitoring Temperature Monitor Design Example The LTC2995 continuously compares the voltage at VPTAT to the voltages at the pins VT1 and VT2 to detect either an overtemperature (OT) or undertemperature (UT) condition. The VT1 comparator output drives the open-drain logic output pin TO1 and the VT2 comparator output drives the open-drain logic output pin TO2. The polarity of these comparisons is configured via the three-state polarity select pin (PS) (Table 3). VCC Open GND The LTC2995 can be configured to give an early warning if the temperature of the internal sensor rises above 60°C and an alarm if the temperature passes 90°C. Tie the DS pin to VCC to select the internal sensor and leave the pin PS unconnected to configure both input voltages VT1 and VT2 as overtemperature thresholds. The voltages at VT1 and VT2 are set to: VT1 =(60K + 273.15K) • 4 Table 3. Temperature Polarity Selection PS PIN pulled low if the voltage VPTAT falls during five consecutive conversions below the undertemperature threshold VT1. Once pulled low, TO1 is released high again if VPTAT rises above VT1 plus an additional hysteresis of about 20mV. Accordingly, T02 is pulled low if the voltage VPTAT rises above the overtemperature threshold VT2 and –once pulled low– TO2 is released high if VPTAT falls below VT2 minus an additional hysteresis of about 20mV. Leaving PS unconnected configures both VT1 and VT2 as overtemperature thresholds and connecting PS to GND configures them both as undertemperature thresholds. If the internal and external sensors are monitored alternately by leaving DS unconnected, VT1 becomes a dedicated threshold for the internal sensor and VT2 becomes a dedicated threshold for the external sensor. FUNCTION CONDITION OUTPUT VT1 Undertemperature Threshold VPTAT < VT1 TO1 Pulled Low VT2 Overtemperature Threshold VPTAT > VT2 TO2 Pulled Low VT1 Overtemperature Threshold VPTAT > VT1 TO1 Pulled Low VT2 Overtemperature Threshold VPTAT > VT2 TO2 Pulled Low VT1 Undertemperature Threshold VPTAT < VT1 TO1 Pulled Low VT2 Undertemperature Threshold VPTAT < VT2 TO2 Pulled Low mV = 1. 332V K VT2 =(90K + 273.15K) • 4 mV = 1.452V K When VPTAT reaches the threshold voltage on pin VT1, TO1 is pulled low indicating an overtemperature early warning. If the temperature reaches 90°C TO2 is also pulled low, indicating an overtemperature alarm. Once the temperature drops below each threshold, the corresponding TO pins will return high after a time-outperiod (tUOTO) set by the capacitor connected to TMR. If pin PS is connected to VCC, the voltage on VT1 becomes an undertemperature threshold and the voltage on VT2 an overtemperature threshold. In this configuration TO1 is 2995f 12 LTC2995 APPLICATIONS INFORMATION Temperature Thresholds The threshold voltages at VT1 and VT2 can be set with the 1.8V reference voltage (VREF) and a resistive divider as shown in Figure 5. VREF = 1.8V RTC η VPTAT SLOPE = ACT t mV K The following design procedure can be used to size the resistive divider. 1. Calculate Threshold Voltages: VT1 = T1 • 4 mV ηACT • K 1.004 VT2 = T2 • 4 1.8V VT2 mV ηACT • K 1.004 where ηACT denotes the actual ideality factor if an external sensor is used and T1 and T2 are the desired threshold temperatures in degrees Kelvin. RTB VT1 O.8V RTA O 200k T1 L T2 T 2995 F05 Figure 5. Temperature Thresholds 2. Choose RTA to obtain the desired VT1 threshold for a desired current through the resistive divider (IREF): R TA = VT1 IREF 3. Choose RTB to obtain the desired VT2 threshold: R TB = VT2 – VT1 IREF 3.3V D+ DS PS VCC LTC2995 VCC VCC + VREF 1.8V 400k 1.2V TO2 – 200k OT ALARM RTC 400k VCC VT2 – 400k + RTB – VT1 RTA UVLO TO1/TO2 PULSE GENERATOR TO1 OT WARNING + VPTAT T/V D– GND 2995 F06 Figure 6. Monitoring Internal Temperature with Two Overtemperature Thresholds 2995f 13 LTC2995 APPLICATIONS INFORMATION 4. Finally RTC is determined by: R TC = 1.8V – VT2 IREF In the Temperature Monitor example discussed earlier with thresholds at VT1 = 60°C and VT2 = 90°C and a desired reference current of 10μA, the required values for RTA, RTB and RTC can be calculated as: 1.332V R TA = = 133.2k 10μA Vn RC LTC2995 VHn – + + – RB UVn 0.5V – VLn + OVn RA 2995 F07 R TB = R TC = 1.452V – 1.332V = 12k 10μA 1.8V – 1.452V = 34.8k 10μA Voltage Monitoring In addition to temperature measurement, the LTC2995 features a low power dual voltage monitoring circuit. Each voltage monitor has two inputs (VH1/VL1 and VH2/VL2) for detecting undervoltage and overvoltage conditions. If either VH1 or VH2 falls below 0.5V (typical), the LTC2995 communicates an undervoltage condition by pulling UV low. Similar, an overvoltage condition is flagged by pulling OV low if either VL1 or VL2 rises above 0.5V. When configured to monitor a positive voltage Vn using the 3-resistor circuit configuration shown in Figure 5, VHn will be connected to the high side tap of the resistive divider and VLn will be connected to the low side tap of the resistive divider. Figure 7. 3-Resistor Positive UV/OV Monitoring For supply monitoring, Vn is the desired nominal operating voltage, In is the desired nominal current through the resistive divider, VOV is the desired overvoltage trip point, and VUV is the desired undervoltage trip point. 1. RA is chosen to set the desired trip point for the overvoltage monitor: RA = 0.5V VN • IN VOV (1) 2. Once RA is known, RB is chosen to set the desired trip point for the undervoltage monitor: RB = 0.5V VN • – RA IN VUV (2) 3. Once, RA and RB are known, RC is determined by: RC = VN – R A – RB IN (3) Voltage Monitor Design Procedure The following 3-step design procedure selects appropriate resistances to obtain the desired UV and OV trip points for the voltage monitor circuit in Figure 7. Voltage Monitor Example A typical voltage monitor application is shown in Figure 2. The monitored voltage is a 5V ±10% supply. Nominal current in the resistive divider is 10μA. 1. Find RA to set the OV trip point of the monitor: RA = 0.5V 5V • ≈ 45.3k 10μA 5.5V 2995f 14 LTC2995 APPLICATIONS INFORMATION 2. Find RB to set the UV trip point of the monitor: RB = 0.5V 5V • – 453 ≅ 10k 10μA 4.5V 3. Determine RC to complete the design: RC = 5V – 453Ω – 100Ω ≈ 442k 10μA The two extreme conditions, with a relative accuracy of 1.5% and resistance accuracy of 1%, result in: ⎛ RC t 0.99 ⎞ VUV(MIN) = 0.5V t 0.985 t ⎜1+ ⎟ ⎝ (RA + RB) t 1.01⎠ and ⎛ RC t 1.01 ⎞ VUV(MAX) = 0.5V t 1.015 t ⎜1+ ⎟ ⎝ (RA + RB) t 0.99 ⎠ Power-Up and Undervoltage Lockout As soon as VCC reaches approximately 1V during power-up, the OV as well as TO1 and TO2 weakly pull to VCC while the UV output asserts low indicating an undervoltage lockout condition. Above VCC = 2V (typical), the VH and VL inputs take control. Once both VH inputs and VCC are valid, an internal timer is started. After an adjustable delay time, UV weakly pulls high. When VCC falls below 1.9V, the LTC2995 indicates again an undervoltage lockout (UVLO) condition by pulling low UV while OV is cleared. For a desired trip point of 4.5V, Therefore, RC =8 RA + RB ⎛ 0.99 ⎞ VUV(MIN) = 0.5V t 0.985 t ⎜1+ 8 ⎟ = 4.3545V 1.01 ⎠ ⎝ and ⎛ 1.01 ⎞ VUV(MAX) = 0.5V t 1.015 t ⎜ 1+ 8 ⎟ = 4.650V 0.99 ⎠ ⎝ Threshold Accuracy Glitch Immunity Reset threshold accuracy is important in a supply sensitive system. Ideally, such a system would only reset if supply voltages fell outside the exact threshold for a specified margin. All LTC2995 VHn/VLn inputs have a relative threshold accuracy of ±1.5% over the full operating temperature range. For example, when the LTC2995 is configured to monitor a 5V input with a 10% tolerance, the desired UV trip point is 4.5V. Because of the ±1.5% relative accuracy of the LTC2995, the UV trip point can be anywhere between 4.433V and 4.567V which is 4.5V ±1.5%. In any supervisory application, noise on the monitored DC voltage can cause spurious resets. To solve this problem without adding hysteresis to the VH/VL comparators, which would add error to the trip voltage, the LTC2995 lowpass filters the output of the comparator. This filter causes the output of the comparator to be integrated before asserting the UV or OV logic. Any transient at the input of the comparator must be of sufficient magnitude and duration before the comparator will trigger the output logic. The Typical Performance Characteristics section shows a graph of the Typical Transient Duration vs Comparator Overdrive. Likewise, the accuracy of the resistances chosen for RA, RB, and RC can affect the UV and OV trip points as well. Using the previous example, if the resistances used to set the UV trip point have 1% accuracy, the UV trip range can grow to between 4.354V and 4.650V. This is illustrated in the following calculations. The UV trip point is given as: ⎛ RC ⎞ VUV = 0.5V t ⎜1+ ⎟ ⎝ RA + RB ⎠ In temperature monitoring, the voltage at VPTAT must exceed a threshold for five consecutive temperature update intervals before the respective TO pin is pulled low. Once the VPTAT voltage crosses back the threshold with an additional 20mV of hysteresis, the respective TO pin is released after a single update interval and an additional delay adjustable by the capacitor on TMR. 2995f 15 LTC2995 APPLICATIONS INFORMATION Timing of Alert Outputs Digital Output Characteristics The LTC2995 has an adjustable timeout period (tUOTO) that holds UV, OV, TO1 or TO2 asserted after any faults have cleared. This delay will minimize the effect of input noise with a frequency above 1/tUOTO. The DC characteristics of the UV, OV, TO1 and TO2 pull-up and pull-down strength are shown in the Typical Performance Characteristics section. Each pin has a weak 400kΩ internal pull-up to VCC and a strong pull-down to ground and can be pulled above VCC. A voltage monitoring example: When any VH drops below its threshold, the UV pin asserts low. When all VH inputs recover above their thresholds, the output timer starts. If all inputs remain above their thresholds when the timer finishes, the UV pin weakly pulls high. However, if any input falls below its threshold during this timeout period, the timer resets and restarts when all inputs are again above the thresholds. A temperature monitoring example: Tying PS to VCC configures TO2 as overtemperature output. In case of an overtemperature condition pin TO2 asserts low. The output timer starts when the temperature crosses back below the threshold minus the temperature hysteresis If the temperature remains below the threshold, the timer finishes and pin TO2 releases high. Selecting the Timing Capacitor The timeout period (tUOTO) for the LTC2995 is adjustable in order to accommodate a variety of applications. Connecting a capacitor, CTMR, between the TMR pin and ground sets the timeout period. The value of capacitor needed for a particular timeout period is: t – 0.5ms CTMR = UOTO 8[ms / nF] The Reset Timeout Period vs Capacitance graph found in the Typical Performance Characteristics section shows the desired delay time as a function of the value of the timer capacitor that should be used. Leaving the TMR pin open with no external capacitor generates a timeout period of approximately 500μs. For long timeout periods, the only limitation is the availability of a large value capacitor with low leakage. Capacitor leakage current must not exceed the minimum TMR charging current of 1.5μA. Tying the TMR pin to VCC will bypass the timeout period and no delay will occur. This arrangement allows these pins to have open-drain behavior while possessing several other beneficial characteristics. The weak pull-up eliminates the need for an external pull-up resistor when the rise time on the pin is not critical. On the other hand, the open drain configuration allows for wired-OR connections and can be useful when more than one signal needs to pull-down on the output. At VCC = 1V, the weak pull-up current is barely turned on. Therefore, an external pull-up resistor of no more than 100k is recommended on the pin if the state and pull-up strength of the pin is crucial at very low VCC. Note however, by adding an external pull-up resistor, the pull-up strength on the pin is increased. Therefore, if it is connected in a wired-OR connection, the pull-down strength of any single device needs to accommodate this additional pull-up strength. Output Rise and Fall Time Estimation The UV, OV, TO1 and TO2 outputs have strong pull-down capability. The following formula estimates the output fall time (90% to 10%) for a particular external load capacitance (CLOAD): tFALL ≈ 2.2 • RPD • CLOAD where RPD is the on-resistance of the internal pull-down transistor estimated to be typically 40Ω at VDD > 1V and at room temperature (25°C), and CLOAD is the external load capacitance on the pin. Assuming a 150pF load capacitance, the fall time is about 13ns. The rise time on the UV, OV, TO1 and TO2 pins is limited by a 400k pull-up resistance to VDD. A similar formula estimates the output rise time (10% to 90%): tRISE ≈ 2.2 • RPU • CLOAD where RPU is the pull-up resistance. 2995f 16 LTC2995 TYPICAL APPLICATIONS ±10% Voltage Monitor (1.8V and 2.5V) and Internal/Remote Overtemperature Monitor 2.5V POWER SUPPLIES 1.8V VCC 0.1μF D+ PS 470pF DS 124k MMBT390 D– VH1 LTC2995 10.2k VPTAT VL1 45.3k TO2 194k TO1 VH2 OV 10.2k UV VL2 VT2 VREF 45.3k 20k VT1 20k GND OT T > 125°C FOR EXTERNAL SENSOR OT T > 75°C FOR INTERNAL SENSOR +10% –10% TMR 5nF 140k 2995 TA02 ±20% Voltage Monitor (12V and 5V) and 0°C to 70°C Internal UT/OT Monitoring with Common Temperature and Powergood LED 12V POWER SUPPLIES 5V VCC 0.1μF D+ PS DS 113k 2.15k D– VH1 LTC2995 2.15k VPTAT VL1 4.12k TO2 442k TO1 VH2 21.5k VL2 41.2k VT2 VREF VT1 GND 28k UT T < 0°C OV +20% UV –20% TMR 2995 TA03 43k OT T > 70°C TEMPERATURE AND POWER GOOD LED 110k 2995f 17 LTC2995 TYPICAL APPLICATIONS Celsius Thermometer and ±10% Voltage Monitor (1.8V and 2.5V) 2.5V POWER SUPPLIES 1.8V 0.1μF D+ VCC 0.1μF 470pF PS 100k + LTC1150 LTC2995 10.2k 4mV/K VL1 VPTAT VH2 OV +10% UV –10% 62k 1k 194k 10.2k VL2 VT2 VT1 GND TO2 TMR 10mV/°C 0V AT 0°C – 143k 45.3k 1.8k 5V 1.8V VREF VH1 45.3k 150k D– DS 124k MMBT3904 1μF –5V TO1 5nF 2995 TA04 ±10% Voltage Monitor (12V and 5V) and –20°C to 70°C Internal UT/OT Monitor with Manual Undervoltage Reset Button 12V POWER SUPPLIES 5V VCC 0.1μF DS 115k MANUAL RESET BUTTON (NORMALLY OPEN) D+ PS D– VH1 LTC2995 1k VPTAT VL1 4.53k TO2 44.2k TO1 VH2 1k VL2 4.53k VT2 VREF VT1 GND OT T > 70°C UT T < –20°C OV +10% UV –10% SYSTEM RESET TMR 2995 TA05 43k 36k 102k 2995f 18 LTC2995 PACKAGE DESCRIPTION Please refer to http://www.linear.com/designtools/packaging/ for the most recent package drawings. UD Package 20-Lead Plastic QFN (3mm × 3mm) (Reference LTC DWG # 05-08-1720 Rev A) 0.70 ±0.05 3.50 ± 0.05 (4 SIDES) 1.65 ± 0.05 2.10 ± 0.05 PACKAGE OUTLINE 0.20 ±0.05 0.40 BSC RECOMMENDED SOLDER PAD PITCH AND DIMENSIONS APPLY SOLDER MASK TO AREAS THAT ARE NOT SOLDERED 3.00 ± 0.10 (4 SIDES) BOTTOM VIEW—EXPOSED PAD R = 0.115 TYP 0.75 ± 0.05 R = 0.05 TYP PIN 1 TOP MARK (NOTE 6) PIN 1 NOTCH R = 0.20 TYP OR 0.25 × 45° CHAMFER 19 20 0.40 ± 0.10 1 2 1.65 ± 0.10 (4-SIDES) (UD20) QFN 0306 REV A 0.200 REF 0.00 – 0.05 NOTE: 1. DRAWING IS NOT A JEDEC PACKAGE OUTLINE 2. DRAWING NOT TO SCALE 3. ALL DIMENSIONS ARE IN MILLIMETERS 4. DIMENSIONS OF EXPOSED PAD ON BOTTOM OF PACKAGE DO NOT INCLUDE MOLD FLASH. MOLD FLASH, IF PRESENT, SHALL NOT EXCEED 0.15mm ON ANY SIDE 5. EXPOSED PAD SHALL BE SOLDER PLATED 6. SHADED AREA IS ONLY A REFERENCE FOR PIN 1 LOCATION ON THE TOP AND BOTTOM OF PACKAGE 0.20 ± 0.05 0.40 BSC 2995f 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 representation that the interconnection of its circuits as described herein will not infringe on existing patent rights. 19 LTC2995 TYPICAL APPLICATION Dual OV/UV ±10% Supply and 75°C/125°C OT/OT Remote Temperature Monitor ASIC/ CPU/ FPGA 2.5V 1.2V D+ 470pF VCC 0.1μF D– PS DS 64.4k VH1 LTC2995 10.2k VL1 45.3k TO2 194k TO1 VH2 10.2k VL2 TMR 45.3k GND 5nF 140k VT1 VT2 20k A/D VPTAT OT T > 125°C OT T > 75°C OV +10% UV –10% VREF 20k 2995 TA06 RELATED PARTS PART NUMBER DESCRIPTION COMMENTS LTC2990 Remote/Internal Temperature, Voltage, Current Monitor I2C Interface LTC2991 Remote/Internal Temperature Sensor I2C Interface, Eight Single-Ended Inputs LTC2997 Remote/Internal Temperature Sensor Analog VPTAT Output Voltage LTC2900 Programmable Quad Supply Monitor Adjustable RESET, 10-Lead MSOP and 3mm × 3mm 10-Lead DFN LTC2901 Programmable Quad Supply Monitor Adjustable RESET and Watchdog Timer, 16-Lead SSOP Package LTC2902 Programmable Quad Supply Monitor Adjustable RESET and Tolerance, 16-Lead SSOP Package, Margining Functions LTC2903 Precision Quad Supply Monitor 6-Lead SOT-23 Package, Ultralow Voltage Reset LTC2904 3-State Programmable Precision Dual Supply Monitor Adjustable Tolerance, 8-Lead SOT-23 Package LTC2905 3-State Programmable Precision Dual Supply Monitor Adjustable RESET and Tolerance, 8-Lead SOT-23 Package LTC2906 Precision Dual Supply Monitor 1-Selectable and One Adjustable Separate VCC Pin, RST/RST Outputs LTC2907 Precision Dual Supply Monitor 1-Selectable and One Adjustable Separate VCC, Adjustable Reset Timer LTC2908 Precision Six Supply Monitor (Four Fixed and Two Adjustable) 8-Lead SOT-23 and DDB Packages LTC2909 Prevision Dual Input UV, OV and Negative Voltage Monitor 2 ADJ Inputs, Monitors Negative Voltages LTC2912 Single UV/OV Positive Voltage Monitor Separate VCC Pin, 8-Lead TSOT and 3mm × 2mm DFN Packages LTC2913 Dual UV/OV Positive Voltage Monitor Separate VCC Pin, 10-Lead MSOP and 3mm × 3mm DFN Packages LTC2914 Quad UV/OV Positive/Negative Voltage Monitor Separate VCC Pin, 16-Lead SSOP and 5mm × 2mm DFN Packages 2995f 20 Linear Technology Corporation LT 0412 • PRINTED IN USA 1630 McCarthy Blvd., Milpitas, CA 95035-7417 (408) 432-1900 ● FAX: (408) 434-0507 ● www.linear.com © LINEAR TECHNOLOGY CORPORATION 2012