FEATURES Temperature Sensor Includes 100 Ω Heater Heater Provides Power IC Emulation Accuracy 63°C typ. from 240°C to 1100°C Operation to 1150°C 5 mV/°C Internal Scale-Factor Resistor Programmable Temperature Setpoints 20 mA Open-Collector Setpoint Outputs Programmable Thermal Hysteresis Internal 2.5 V Reference Single 5 V Operation 400 µA Quiescent Current (Heater OFF) Minimal External Components Airflow and Temperature Sensor TMP12* FUNCTIONAL BLOCK DIAGRAM VREF HYSTERESIS CURRENT The TMP12 is a silicon-based airflow and temperature sensor designed to be placed in the same airstream as heat generating components that require cooling. Fan cooling may be required continuously, or during peak power demands, e.g. for a power supply, and if the cooling systems fails, system reliability and/or safety may be impaired. By monitoring temperature while emulating a power IC, the TMP12 can provide a warning of cooling system failure. The TMP12 generates an internal voltage that is linearly proportional to Celsius (Centigrade) temperature, nominally 15 mV/°C. The linearized output is compared with voltages from an external resistive divider connected to the TMP12’s 2.5 V precision reference. The divider sets up one or two reference voltages, as required by the user, providing one or two temperature setpoints. Comparator outputs are open-collector transistors able to sink over 20 mA. There is an on-board hysteresis generator provided to speed up the temperature-setpoint output transitions, this also reduces erratic output transitions in noisy environments. Hysteresis is programmed by the external resistor chain and is determined by the total current drawn from the 2.5 V reference. The TMP12 airflow sensor also incorporates a precision, low temperature coefficient 100 Ω heater resistor that may be connected directly to an external 5 V supply. When the heater is activated it raises the die temperature in IHYS SET HIGH - OVER + WINDOW COMPARATOR SET LOW GND + VOLTAGE REFERENCE AND SENSOR 1kΩ UNDER HYSTERESIS VOLTAGE HEATER 100Ω APPLICATIONS System Airflow Sensor Equipment Over-Temperature Sensor Over-Temperature Protection Power Supply Thermal Sensor Low-Cost Fan Controller GENERAL DESCRIPTION V+ CURRENT MIRROR + a PINOUTS DIP And SO VREF 1 8 V+ SET HIGH 2 7 OVER 6 UNDER 5 HEATER SET LOW 3 GND 4 TOP VIEW (Not to Scale) the DIP package approximately 20°C above ambient (in still air). The purpose of the heater in the TMP12 is to emulate a power IC, such as a regulator or Pentium CPU which has a high internal dissipation. When subjected to a fast airflow, the package and die temperatures of the power device and the TMP12 (if located in the same airstream) will be reduced by an amount proportional to the rate of airflow. The internal temperature rise of the TMP12 may be reduced by placing a resistor in series with the heater, or reducing the heater voltage. The TMP12 is intended for single 5 V supply operation, but will operate on a 12 V supply. The heater is designed to operate from 5 V only. Specified temperature range is from 240°C to 1125°C, operation extends to 1150°C at 5 V with reduced accuracy. The TMP12 is available in 8-pin plastic DIP and SO packages. *Protected by U.S. Patent No. 5,195,827. REV. 0 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 which may result from its use. No license is granted by implication or otherwise under any patent or patent rights of Analog Devices. © Analog Devices, Inc., 1995 One Technology Way, P.O. Box 9106, Norwood. MA 02062-9106, U.S.A. Tel: 617/329-4700 Fax: 617/326-8703 TMP12–SPECIFICATIONS (V = 15 V, 240°C ≤ T ≤ 1125°C unless otherwise noted.) S Parameter ACCURACY Accuracy (High, Low Setpoints) Accuracy (High, Low Setpoints) Internal Scale Factor Power Supply Rejection Ratio Linearity Repeatability Long Term Stability Symbol Conditions PSRR TA = 125°C TA = 240°C to 1100°C TA = 240°C to 1100°C 4.5 V ≤ 1VS ≤ 5.5 V TA = 240°C to 1125°C TA = 240°C to 1125°C TA = 1125°C for 1 k Hrs SETPOINT INPUTS Offset Voltage Output Voltage Drift Input Bias Current VOS TCVOS IB VREF OUTPUT Output Voltage Output Voltage VREF VREF Output Drift Output Current, Zero Hysteresis Hysteresis Current Scale Factor OPEN-COLLECTOR OUTPUTS Output Low Voltage Output Low Voltage Output Leakage Current Fall Time HEATER Resistance Temperature Coefficient Maximum Continuous Current POWER SUPPLY Supply Range Supply Current A Min 14.9 Typ Max Units 62 63 15 0.1 0.5 0.3 0.3 63 65 15.1 0.5 °C °C mV/°C °C/V °C °C °C 0.25 3 25 TA = 125°C, No Load TA = 240°C to 1100°C, No Load 2.49 TCVREF IVREF SFHYS VOL VOL IOH tHL I SINK = 1.6 mA I SINK = 20 mA VS = 12 V See Test Load RH IH TA = 125°C TA = 240°C to 1125°C See Note 1 1VS ISY ISY Unloaded at 15 V Unloaded at 112 V2 97 100 mV µV/°C nA 2.50 2.51 2.5 60.015 V V 210 7 5 ppm/°C µA µA/°C 0.25 0.6 1 40 0.4 100 100 103 100 60 4.5 400 450 5.5 600 V V µA ns Ω ppm/°C mA V µA µA NOTES 1Guaranteed but not tested. 2TMP12 is specified for operation from a 5 V supply. However, operation is allowed up to a 12 V supply, but not tested at 12 V. Maximum heater supply is 6 V. Specifications subject to change without notice. TEST LOAD 1kΩ 20pF –2– REV. 0 TMP12 WAFER TEST LIMITS (V S = 15 V, GND = O V, TA = 125°C, unless otherwise noted.) Parameter Symbol ACCURACY Accuracy (High, Low Setpoints) Internal Scale Factor Conditions Min Typ Max Units TA = 125°C TA = 125°C 14.9 15 63 15.1 °C mV/°C 100 nA 2.51 V 0.4 100 V µA 103 Ω 5.5 600 V µA SETPOINT INPUTS Input Bias Current IB VREF OUTPUT Output Voltage VREF T A = 125°C, No Load OPEN-COLLECTOR OUTPUTS Output Low Voltage Output Leakage Current VOL IOH ISINK = 1.6 mA VS = 12 V HEATER Resistance RH TA = 125°C POWER SUPPLY Supply Range Supply Current 1VS ISY Unloaded at 15 V 2.49 97 4.5 100 NOTE Electrical tests are performed at wafer probe to the limits shown. Due to variations in assembly methods and normal yield loss, yield after packaging is not guaranteed for standard product dice. Consult factory to negotiate specifications based on dice lot qualification through sample lot assembly and testing. DICE CHARACTERISTICS Die Size 0.078 3 0.071 inch, 5,538 sq. mils (1.98 3 1.80 mm, 3.57 sq. mm) Transistor Count: 105 8 7 6 5 1. VREF 2. SET HIGH INPUT 3. SET LOW INPUT 4. GND 5. HEATER 6. UNDER OUTPUT 7. OVER OUTPUT 8. V1 1 2 3 4 For additional DICE ordering information, refer to databook. CAUTION ESD (electrostatic discharge) sensitive device. Electrostatic charges as high as 4000 V readily accumulate on the human body and test equipment and can discharge without detection. Although the TMP12 features proprietary ESD protection circuitry, permanent damage may occur on devices subjected to high energy electrostatic discharges. Therefore, proper ESD precautions are recommended to avoid performance degradation or loss of functionality. REV. 0 –3– WARNING! ESD SENSITIVE DEVICE TMP12 ABSOLUTE MAXIMUM RATINGS* FUNCTIONAL DESCRIPTION Supply Voltage . . . . . . . . . . . . . . . . . . . . . . . . 20.3 V to 115 V Heater Voltage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16 V Setpoint Input Voltage . . . . . . . . . . . 20.3 V to [(V1) 10.3 V] Reference Output Current . . . . . . . . . . . . . . . . . . . . . . . . 2 mA Open-Collector Output Current . . . . . . . . . . . . . . . . . . 50 mA Open-Collector Output Voltage . . . . . . . . . . . . . . . . . . . 115 V Operating Temperature Range . . . . . . . . . . 255°C to 1150°C Dice Junction Temperature . . . . . . . . . . . . . . . . . . . . . 1175°C Storage Temperature Range . . . . . . . . . . . . 265°C to 1160°C Lead Temperature(Soldering, 60 sec) . . . . . . . . . . . . . 1300°C The TMP12 incorporates a heating element, temperature sensor, and two user-selectable setpoint comparators on a single substrate. By generating a known amount of heat, and using the setpoint comparators to monitor the resulting temperature rise, the TMP12 can indirectly monitor the performance of a system’s cooling fan. Package Type ΘJA ΘJC Units 8-Pin Plastic DIP (P) 8-Lead SOIC (S) 1031 1582 43 43 °C/W °C/W NOTES 1 ΘJA is specified for device in socket (worst case conditions). 2 ΘJA is specified for device mounted on PCB. The TMP12 temperature sensor section consists of a bandgap voltage reference which provides both a constant 2.5 V output and a voltage which is proportional to absolute temperature (VPTAT). The VPTAT has a precise temperature coefficient of 5 mV/K and is 1.49 V (nominal) at 125°C. The comparators compare VPTAT with the externally set temperature trip points and generate an open-collector output signal when one of their respective thresholds has been exceeded. The heat source for the TMP12 is an on-chip 100 Ω low tempco thin-film resistor. When connected to a 5 V source, this resistor dissipates: CAUTION 1. Stresses above those listed under “Absolute Maximum Ratings” may cause permanent damage to the device. This is a stress rating only and functional operation at or above this specification is not implied. Exposure to the above maximum rating conditions for extended periods may affect device reliability. 2. Digital inputs and outputs are protected, however, permanent damage may occur on unprotected units from high-energy electrostatic fields. Keep units in conductive foam or packaging at all times until ready to use. Use proper antistatic handling procedures. 3. Remove power before inserting or removing units from their sockets. PD = 52 V V2 = = 0.25 W , 100 Ω R which generates a temperature rise of about 32°C in still air for the SO packaged device. With an airflow of 450 feet per minute (FPM), the temperature rise is about 22°C. By selecting a temperature setpoint between these two values, the TMP12 can provide a logic-level indication of problems in the cooling system. A proprietary, low tempco thin-film resistor process, in conjunction with production laser trimming, enables the TMP12 to provide a temperature accuracy of 63°C (typ) over the rated temperature range. The open-collector outputs are capable of sinking 20 mA, allowing the TMP12 to drive small control relays directly. Operating from a single 15 V supply, the quiescent current is only 600 µA (max), without the heater resistor current. ORDERING GUIDE Model/Grade Temperature Range1 Package Description Package Option TMP12FP TMP12FS TMP12GBC XIND XIND 125°C Plastic DIP SOIC Die N-8 SO-8 NOTE 1XIND = 240°C to 1125°C –4– REV. 0 140 35 V = 5V SO–8 SOLDERED TO .5 " TRANSITION FROM 100°C STIRRED BATH TO FORCED 25°C AIR .3" Cu PCB 120 30 a 25 a. 0 FPM 20 b. 250 FPM c. 450 FPM 15 c d. 600 FPM d 10 5V, NO LOAD, HEATER OFF .3" Cu PCB PDIP SOLDERED TO 2" 1.31" Cu PCB 80 60 a. PDIP PCB b. SOIC PCB a 40 b 20 5 0 50 100 150 200 HEATER RESISTOR POWER DISSIPATION – mW 0 0 250 200 100 300 400 500 AIR VELOCITY – FPM 600 700 Figure 4. Package Thermal Time Constant in Forced Air Figure 1. SOIC Junction Temperature Rise vs. Heater Dissipation 120 25 V = 5V PDIP SOLDERED TO 2" c b 20 100 a a. 0 FPM b. 250 FPM 15 c. 450 FPM d. 600 FPM d 10 5 TRANSITION FROM STILL 25°C AIR TO STIRRED 100°C BATH 110 1.31" Cu PCB JUNCTION TEMPERATURE – °C JUNCTION TEMPERATURE RISE ABOVE AMBIENT – °C 100 = SO–8 SOLDERED TO .5" AIR FLOW RATES 0 AIR FLOW RATES a 90 80 V 70 b 60 = 5V, NO LOAD, HEATER OFF SO–8 SOLDERED TO .5" .3" Cu PCB PDIP SOLDERED TO 2" 1.31" Cu PCB 50 40 30 a. SO–8 PCB 20 b. PDIP PCB 10 0 0 0 50 100 150 200 HEATER RESISTOR POWER DISSIPATION – mW 0 250 Figure 2. PDIP Junction Temperature Rise vs. Heater Dissipation 2 4 6 8 10 12 TIME – sec 14 16 18 20 Figure 5. Thermal Response Time in Stirred Oil Bath 102 70 a. SO–8, HTR @ 5V b. PDIP, HTR @ 5V c. SO–8, HTR @ 3V d. PDIP, HTR @ 3V 65 60 55 a 101.5 V+ = +5V b HEATER RESISTANCE – Ω JUNCTION TEMPERATURE – °C V b TIME CONSTANT – sec JUNCTION TEMPERATURE RISE ABOVE AMBIENT – °C TMP12 50 45 40 35 30 25 c 20 V = 5V RHEATER TO EXTERNAL SUPPLY TURNED ON @ t = 5 sec SO–8 SOLDERED TO .5" .3" COPPER PCB PDIP SOLDERED TO 2" 1.31 COPPER PCB 15 10 d 101 100.5 100 99.5 99 98.5 5 0 0 10 20 30 40 50 60 70 80 TIME – sec 98 -75 90 100 110 120 130 Figure 3. Junction Temperature Rise in Still Air REV. 0 -25 25 75 TEMPERATURE – °C 125 Figure 6. Heater Resistance vs. Temperature –5– 175 TMP12 2.52 6 V = 5V, NO LOAD, HEATER OFF 5 4 3 ACCURACY ERROR – °C REFERENCE VOLTAGE – V 2.515 2.51 2.505 2.5 a. MAXIMUM LIMIT 2 b. ACCURACY ERROR b a 1 c. MINIMUM LIMIT 0 -1 -2 c -3 -4 2.495 -5 2.49 -75 -25 25 75 TEMPERATURE – °C 125 -6 -50 175 Figure 7. Reference Voltage vs. Temperature 0 25 50 75 TEMPERATURE – °C 100 125 Figure 10. Accuracy Error vs. Temperature 5 500 START-UP VOLTAGE DEFINED AS OUTPUT READING BEING WITHIN 5 °C OF OUTPUT AT 450 5V 400 4.5 SUPPLY CURRENT – µA START-UP SUPPLY VOLTAGE – V -25 NO LOAD, HEATER OFF 4 3.5 350 300 250 200 150 Ta = 25°C, NO LOAD, HEATER OFF 100 50 3 -75 -25 25 75 TEMPERATURE – °C 125 0 175 Figure 8. Start-up Voltage vs. Temperature 0 1 2 3 4 5 SUPPLY VOLTAGE – V 6 7 8 Figure 11. Supply Current vs. Supply Voltage 500 0.5 V = 5V, NO LOAD, HEATER OFF POWER SUPPLY REJECTION – °C/V 475 SUPPLY CURRENT – µA 450 425 400 375 350 325 300 -75 -25 25 75 TEMPERATURE – °C Figure 9. Supply Current vs. Temperature 125 V 0.4 4.5 TO 5.5V 0.3 0.2 0.1 0 -75 175 = NO LOAD, HEATER OFF -25 25 75 TEMPERATURE – °C 125 175 Figure 12. VPTAT Power Supply Rejection vs. Temperature –6– REV. 0 TMP12 40 OPEN–COLLECTOR OUTPUT VOLTAGE – mV 700 OPEN COLLECTOR SINK CURRENT – mA 38 36 34 32 30 28 VOL = 26 1V, V = 5V 24 22 20 -75 -25 25 75 TEMPERATURE – °C 125 600 Figure 13. Open-Collector Output Sink Current vs. Temperature a b. LOAD = 5mA 500 c. LOAD = 1mA 400 b 300 200 V = c 5V 100 0 -75 175 a. LOAD = 10mA -25 25 75 TEMPERATURE – °C 125 175 Figure 14. Open-Collector Voltage vs. Temperature APPLICATIONS INFORMATION Temperature Hysteresis A typical application for the TMP12 is shown in Figure 15. The TMP12 package is placed in the same cooling airflow as a high-power dissipation IC. The TMP12’s internal resistor produces a temperature rise which is proportional to air flow, as shown in Figure 16. Any interruption in the airflow will produce an additional temperature rise. When the TMP12 chip temperature exceeds a user-defined setpoint limit, the system controller can take corrective action, such as: reducing clock frequency, shutting down unneeded peripherals, turning on additional fan cooling, or shutting down the system. The temperature hysteresis at each setpoint is the number of degrees beyond the original setpoint temperature that must be sensed by the TMP12 before the setpoint comparator will be reset and the output disabled. Hysteresis prevents “chatter” and “motorboating” in feedback control systems. For monitoring temperature in computer systems, hysteresis prevents multiple interrupts to the CPU which can reduce system performance. PGA PACKAGE PGA SOCKET POWER I.C. Figure 17 shows the TMP12’s hysteresis profile. The hysteresis is programmed, by the user, by setting a specific load current on the reference voltage output VREF. This output current, IREF, is also called the hysteresis current. IREF is mirrored internally by the TMP12, as shown in the functional block diagram, and fed to a buffer with an analog switch. AIR FLOW PC BOARD TMP12 HYSTERESIS LOW HYSTERESIS HIGH HI Figure 15. Typical Application HYSTERESIS HIGH = HYSTERESIS LOW OUTPUT VOLTAGE OVER, UNDER 65 a DIE TEMPERATURE (°C) 60 b LO 55 TEMPERATURE c 50 TSETLOW d Figure 17. TMP12 Hysteresis Profile 45 a. TMP12 DIE TEMP NO AIR FLOW b. HIGH SET POINT c. LOW SET POINT d. TMP12 DIE TEMP MAX AIR FLOW e. SYSTEM AMBIENT TEMPERATURE 40 After a temperature setpoint has been exceeded and a comparator tripped, the hysteresis buffer output is enabled. The result is a current of the appropriate polarity which generates a hysteresis offset voltage across an internal 1 kΩ resistor at the comparator input. The comparator output remains “on” until the voltage at the comparator input, now equal to the temperature sensor voltage VPTAT summed with the hysteresis effect, has returned to the programmed setpoint voltage. The comparator then returns e 35 0 50 100 150 200 250 TMP12 PD (mW) Figure 16. Choosing Temperature Setpoints REV. 0 TSETHIGH –7– TMP12 LOW, deactivating the open-collector output and disabling the hysteresis current buffer output. The scale factor for the programmed hysteresis current is: I = IVREF = 5 µA/°C 1 7 µA Thus, since VREF = 2.5 V, a reference load resistance of 357 kΩ or greater (output current of 7 µA or less) will produce a temperature setpoint hysteresis of zero degrees. For more details, see the temperature programming discussion below. Larger values of load resistance will only decrease the output current below 7 µA, but will have no effect on the operation of the device. The amount of hysteresis is determined by selecting an appropriate value of load resistance for VREF, as shown below. Programming the TMP12 The basic thermal monitoring application only requires a simple three-resistor ladder voltage divider to set the high and low setpoints and the hysteresis. These resistors are programmed in the following sequence: 1. Select the desired hysteresis temperature. 2. Calculate the hysteresis current, IVREF 3. Select the desired setpoint temperatures. 4. Calculate the individual resistor divider ladder values needed to develop the desired comparator setpoint voltages at the Set High and Set Low inputs. For example, setting the high setpoint for 180°C, the low setpoint for 155°C, and hysteresis for 3°C produces the following values: IHYS = IVREF = (3°C 3 5 µA/°C) 1 7 µA = 15 µA 1 7 µA = 22 µA VSETHIGH = (TSETHIGH 1 273.15)(5 mV/°C) = (80°C 1 273.15)(5 mV/°C) = 1.766 V VSETLOW = (TSETLOW 1 273.15)(5 mV/°C) = (55°C 1 273.15) (5 mV/°C) = 1.641 V R1 (kΩ) = (VREF 2 VSETHIGH)/IVREF = (2.5 V 2 1.766 V)/ 22 µA = 33.36 kΩ R2 (kΩ) = (VSETHIGH 2 VSETLOW)/IVREF = (1.766 V 2 1.641 V)/ 22 µA = 5.682 kΩ R3 (kΩ) = VSETLOW / IVREF = (1.641 V)/22 µA = 74.59 kΩ The total of R1 1 R2 1 R3 is equal to the load resistance needed to draw the desired hysteresis current from the reference, or IVREF . The nomograph of Figure 19 provides an easy method of determining the correct VPTAT voltage for any temperature. Simply locate the desired temperature on the appropriate scale (K, °C or °F) and read the corresponding VPTAT value from the bottom scale. The hysteresis current is readily calculated, as shown above. For example, to produce 2 degrees of hysteresis IVREF should be set to 17 µA. Next, the setpoint voltages VSETHIGH and VSETLOW are determined using the VPTAT scale factor of 5 mV/K = 5 mV/ (°C 1 273.15), which is 1.49 V for 125°C. Finally, the divider resistors are calculated, based on the setpoint voltages. 218 248 –55 –25 –18 273 298 323 348 373 398 0 25 50 75 100 125 K °C –67 –25 0 32 50 77 100 150 200 212 257 1.865 1.99 °F 1.09 1.24 1.365 1.49 1.615 1.74 VPTAT The setpoint voltages are calculated from the equation: VSET = (TSET 1 273.15)(5 mV/°C) Figure 19. Temperature 2 VPTAT Scale This equation is used to calculate both the VSETHIGH and the VSETLOW values. A simple 3-resistor network, as shown in Figure 18, determines the setpoints and hysteresis value. The equations used to calculate the resistors are: The formulas shown above are also helpful in understanding the calculations of temperature setpoint voltages in circuits other than the standard two-temperature thermal/airflow monitor. If a setpoint function is not needed, the appropriate comparator input should be disabled. SETHIGH can be disabled by tying it to V1 or VREF, SETLOW by tying it to GND. Either output can be left disconnected. R1 (kΩ) = (VREF 2 VSETHIGH )/IVREF = (2.5 V 2 VSETHIGH )/IVREF R2 (kΩ) = (VSETHIGH 2 VSETLOW)/IVREF R3 (kΩ) = VSETLOW/IVREF VREF = 2.5 V Selecting Setpoints 8 V+ 7 OVER 3 6 UNDER 4 5 HEATER 1 (VREF – VSETHIGH) / IVREF = R1 IVREF VSETHIGH 2 TMP12 (VSETHIGH – VSETLOW) / IVREF = R2 VSETLOW VSETLOW / IVREF = R3 GND Figure 18. TMP12 Setpoint Programming Choosing the temperature setpoints for a given system is an empirical process, because of the wide variety of thermal issues in any practical design. The specific setpoints are dependent on such factors as airflow velocity in the system, adjacent component location and size, PCB thickness, location of copper ground planes, and thermal limits of the system. The TMP12’s temperature rise above ambient is proportional to airflow (Figures 1, 2 and 16). As a starting point, the low setpoint temperature could be set at the system ambient temperature (inside the enclosure) plus one half of the temperature rise above ambient (at the actual airflow in the system). With this setting, the low limit will provide a warning either if the fan output is reduced or if the ambient temperature rises (for example, if the fan’s cool air intake is blocked). The high setpoint could then be set for the maximum system temperature to provide a final system shutdown control. –8– REV. 0 TMP12 eters which are adjusted to 8-bit resolution via a 3-wire serial interface. The controller simply sweeps the wiper of potentiometer 1 from the A1 terminal to the B1 terminal (digital value = 0), while monitoring the comparator output at Pin 7 of the TMP12. When Pin 7 goes low, the voltage at Pin 2 equals the VPTAT voltage. This Circuit sweeps Pin 2's voltage from maximum to minimum, so that the TMP12's setpoint hystersis will not affect the reading. Measuring the TMP12 Internal Temperature As previously mentioned, the TMP12’s VPTAT generator represents the chip temperature with a slope of 5 mV/K. In some cases, selecting the setpoints is made easier if the TMP12’s internal VPTAT voltage (and therefore the chip temperature) is known. For example, the case temperature of a high power microprocessor can be monitored with a thermistor, thermocouple, or other measurement method. The case temperature can then be correlated with the TMP12’s temperature to select the setpoints. The circuit of Figure 21 provides approximately 1°C of resolution. The two potentiometers divide VREF by two, and the 8-bit potentiometer further divides VREF by 256, so the resolution is: The TMP12’s VPTAT voltage is not available externally, so indirect methods must be used. Since the VPTAT voltage is applied to the internal comparators, measuring the voltage at which the digital output changes state will reflect the VPTAT voltage. TMP12 1 VPTAT 2 R1 Resolution = V+ SET HIGH OVER 330 +5V LED 200K 3 R1 SET LOW UNDER GND HEATER 6 2 = 4.9 mV 28 NC VPTAT = 1.25 V + (Digital Count 200K 4 = where VREF is the voltage reference output (Pin 1 of the TMP12) and N is the resolution of the AD8402. Since the VPTAT has a slope of 5 mV/K, the AD8402 provides 1°C of resolution. The adjustment range of this circuit extends from VREF/2 (i.e. 1.25 V, or 223°C) to VREF 2 1 LSB (i.e. 2.5 V 2 4.9 mV, or 226°C). The VPTAT is therefore: 8 7 2 2N +5V VREF 2.5 V VREF A simple method of measuring the TMP12 VPTAT is shown in Figure 20. To measure VPTAT, adjust potentiometer R1 until the LED turns ON. The voltage at Pin 2 of the TMP12 will then match the TMP12’s internal VPTAT. 5 4.9 mV) +5V where Digital Count is the value sent to the AD8402 which caused the setpoint 1 output to go LOW. A third way to measure the VPTAT voltage is to close a feedback loop around one of the TMP12’s comparators. This causes the comparator to oscillate, and in turn forces the voltage at the comparator input to equal the VPTAT voltage. Figure 22 is a typical circuit for this measurement. An OP193 operational amplifier, operating as an integrator, provides additional loop-gain to ensure that the TMP12 comparator will oscillate. Figure 20. Measuring VPTAT with a Potentiometer The method described in Figure 20 can be automated by replacing the discrete resistors with a digital potentiometer. The improved circuit, shown in Figure 21, permits the VPTAT voltage to be monitored with a microprocessor or other digital controller. The AD8402-100 provides two 100 kΩ potentiomµC INTERFACE OVER +5V 6 10 SHDN RS 11 V AD8402–100 SDI CLK 9 8 A1 13 W1 12 B1 14 1 DD SERIAL DATA INTERFACE 7 A2 3 W2 4 VPTAT 8 7 2 3 NC CS B2 VREF TEMPERATURE SENSOR & VOLTAGE REFERENCE 4 WINDOW COMPARATOR HYSTERESIS GENERATOR 2 100 TMP12 AGND 1 DGND 5 Figure 21. Measuring VPTAT with a Digital Potentiometer REV. 0 –9– 6 NC 5 +5V TMP12 due to IR voltage drops and coupling of external noise sources. In any case, a 0.1 µF capacitor for power supply bypassing is always recommended at the chip. Understanding Error Sources The accuracy of the VPTAT sensor output is well characterized and specified, however preserving this accuracy in a thermal monitoring control system requires some attention to minimizing the various potential error sources. The internal sources of setpoint programming error include the initial tolerances and temperature drifts of the reference voltage VREF, the setpoint comparator input offset voltage and bias current, and the hysteresis current scale factor. When evaluating setpoint programming errors, remember that any VREF error contribution at the comparator inputs is reduced by the resistor divider ratios. Each comparator’s input bias current drops to less than 1 nA (typ) when the comparator is tripped. This change accounts for some setpoint voltage error, equal to the change in bias current multiplied by the effective setpoint divider ladder resistance to ground. Safety Considerations in Heating and Cooling System Design Designers should anticipate potential system fault conditions that may result in significant safety hazards which are outside the control of and cannot be corrected by the TMP12-based circuit. Governmental and Industrial regulations regarding safety requirements and standards for such designs should be observed where applicable. Self-Heating Effects In some applications the user should consider the effects of selfheating due to the power dissipated by the open-collector outputs, which are capable of sinking 20 mA continuously. Under full load, the TMP12 open-collector output device is dissipating: PDISS = 0.6 V The thermal mass of the TMP12 package and the degree of thermal coupling to the surrounding circuitry are the largest factors in determining the rate of thermal settling, which ultimately determines the rate at which the desired temperature measurement accuracy may be reached (see graph in Figure 3). Thus, one must allow sufficient time for the device to reach the final temperature. The typical thermal time constant for the SOIC plastic package is approximately 70 seconds in still air. Therefore, to reach the final temperature accuracy within 1%, for a temperature change of 60 degrees, a settling time of 5 time constants, or 6 minutes, is necessary. Refer to Figure 4. 0.020 A = 12 mW which in a surface-mount SO package accounts for a temperature increase due to self-heating of: ∆T = PDISS JA = 0.012 W 158°C/W = 1.9°C This increase is for still air, of course, and will be reduced at high airflow levels. However, the user should still be aware that self-heating effects can directly affect the accuracy of the TMP12. For setpoint 2, self-heating will add to the setpoint temperature (that is, in the above example the TMP12 will switch the setpoint 2 output off 1.9 degrees early). Self-heating will not affect the temperature at which setpoint 1 turns on, but will add to the hysteresis. Several circuits for adding external driver transistors and other buffers are presented in following sections of this data sheet. These buffers will reduce self-heating and improve accuracy. External error sources to consider are the accuracy of the external programming resistors, grounding error voltages, and thermal gradients. The accuracy of the external programming resistors directly impacts the resulting setpoint accuracy. Thus, in fixed-temperature applications the user should select resistor tolerances appropriate to the desired programming accuracy. Since setpoint resistors are typically located in the same air flow as the TMP12, resistor temperature drift must be taken into account also. This effect can be minimized by selecting good quality components, and by keeping all components in close thermal proximity. Careful circuit board layout and component placement are necessary to minimize common thermal error sources. Also, the user should take care to keep the bottom of the setpoint programming divider ladder as close to GND (Pin 4) as possible to minimize errors Buffering the Voltage Reference The reference output VREF is used to generate the temperature setpoint programming voltages for the TMP12. Since the hysteresis is set by the reference current, external circuits which draw current from the reference will increase the hysteresis value. +5V 1uF NC 1 V+ VREF 2 SET HIGH 3 SET LOW 4 GND OVER UNDER HEATER 5k 8 200k 7 6 5 300k NC +5V +5V OP193 10k ~1.5V TMP12 VPTAT 130k 0.1UF Figure 22. An Analog Measurement Circuit for VPTAT –10– REV. 0 TMP12 The on-board VREF output buffer is typically capable of 500 µA output drive into as much as 50 pF load (max). Exceeding this load will affect the accuracy of the reference voltage, could cause thermal sensing errors due to excess heat build-up, and may induce oscillations. External buffering of VREF with a low-drift voltage follower will ensure optimal reference accuracy. Amplifiers which offer low drift, low power consumption, and low cost appropriate to this application include the OP284, and members of the OP113 and OP193 families. With excellent drift and noise characteristics, VREF offers a good voltage reference for data acquisition and transducer excitation applications as well. Output drift is typically better than 210 ppm/°C, with 315 nV/Hz (typ) noise spectral density at 1 kHz. Preserving Accuracy Over Wide Temperature Range Operation The TMP12 is unique in offering both a wide-range temperature sensor and the associated detection circuitry needed to implement a complete thermostatic control function in one monolithic device. The voltage reference, setpoint comparators, and output buffer amplifiers have been carefully compensated to maintain accuracy over the specified temperature ranges in this application. Since the TMP12 is both sensor and control circuit, in many applications the external components used to program and interface the device are subjected to the same temperature extremes. Thus, it is necessary to place components in close thermal proximity minimizing large temperate differentials, and to account for thermal drift errors where appropriate, such as resistor matching temperature coefficients, amplifier error drift, and the like. Circuit design with the TMP12 requires a slightly different perspective regarding the thermal behavior of electronic components. Switching Loads with the Open-Collector Outputs In many temperature sensing and control applications some type of switching is required. Whether it be to turn on a heater when the temperature goes below a minimum value or to turn off a motor that is overheating, the open-collector outputs can be used. For the majority of applications, the switches used need to handle large currents on the order of 1 Amp and above. Because the TMP12 is accurately measuring temperature, the open-collector outputs should handle less than 20 mA of current to minimize self-heating. Clearly, the trip point outputs should not drive the equipment directly. Instead, an external switching device is required to handle the large currents. Some examples of these are relays, power MOSFETs, thyristors, IGBTs, and Darlington transistors. This section shows a variety of circuits where the TMP12 controls a switch. The main consideration in these circuits, such as the relay in Figure 23, is the current required to activate the switch. +12V R1 3 Thermal Response Time The time required for a temperature sensor to settle to a specified accuracy is a function of the thermal mass of the sensor, and the thermal conductivity between the sensor and the object being sensed. Thermal mass is often considered equivalent to capacitance. Thermal conductivity is commonly specified using the symbol Q, and is the inverse of thermal resistance. It is commonly specified in units of degrees per watt of power transferred across the thermal joint. Figures 3 and 5 illustrate the typical RC time constant response to a step change in ambient temperature. Thus, the time required for the TMP12 to settle to the desired accuracy is dependent on the package selected, the thermal contact established in the particular application, and the equivalent thermal conductivity of the heat source. For most applications, the settling-time is probably best determined empirically. REV. 0 MOTOR SHUTDOWN 7 2 R2 WINDOW COMPARATOR 2604-12-311 COTO NC 6 R3 140Ω 4 PC Board Layout Considerations The TMP12 also requires a different perspective on PC board layout. In many applications, wide traces and generous ground planes are used to extract heat from components. The TMP12 is slightly different, in that ideal path for heat is via the cooling system air flow. Thus, heat paths through the PC traces should be minimized. This constraint implies that minimum pad sizes and trace widths should be specified in order to reduce heat conduction. At the same time, analog performance should not be compromised. In particular, the bottom of the setpoint resistor ladder should be located as close to GND as possible, as discussed in the Understanding Error Sources section of this data sheet. VREF TEMPERATURE VPTAT SENSOR & 1 8 VOLTAGE IN4001 REFERENCE OR EQUIV 5 HYSTERESIS GENERATOR +12 V 100 TMP12 Figure 23. Reed Relay Drive It is important to check the particular relay you choose to ensure that the current needed to activate the coil does not exceed the TMP12’s recommended output current of 20 mA. This is easily determined by dividing the relay coil voltage by the specified coil resistance. Keep in mind that the inductance of the relay will create large voltage spikes that can damage the TMP12 output unless protected by a commutation diode across the coil, as shown. The relay shown has contact rating of 10 Watts maximum. If a relay capable of handling more power is desired, the larger contacts will probably require a commensurably larger coil, with lower coil resistance and thus higher trigger current. As the contact power handling capability increases, so does the current needed for the coil, In some cases an external driving transistor should be used to remove the current load on the TMP12 as explained in the next section. –11– TMP12 Power FETs are popular for handling a variety of high current dc loads. Figure 24 shows the TMP12 driving a P-channel MOSFET transistor for a simple heater circuit. When the output transistor turns on, the gate of the MOSFET is pulled down to approximately 0.6 V, turning it on. For most MOSFETs a gate-to-source voltage or Vgs on the order of -2 V to -5 V is sufficient to turn the device on. Figure 25 shows a similar circuit for turning on an N-channel MOSFET, except that now the gate to source voltage is positive. For this reason an external transistor must be used as an inverter so that the MOSFET will turn on when the trip point pulls down. 1 VREF TEMPERATURE VPTAT V+ SENSOR & 8 VOLTAGE REFERENCE 4.7kΩ 4.7kΩ MOTOR CONTROL 7 NC 2 IRGBC40S 3 4 WINDOW COMPARATOR 2N1711 6 5 +5V HYSTERESIS GENERATOR 100 TMP12 1 VREF TEMPERATURE VPTAT SENSOR & 8 VOLTAGE REFERENCE 2 3 4 7 WINDOW COMPARATOR V+ NC NC = NO CONNECT 2.4kΩ (12V) 1.2kΩ (6V) 5% 6 5 HYSTERESIS GENERATOR Figure 26. Driving an IGBT IRFR9024 OR EQUIV The last class of high power devices discussed here are Thyristors, which include SCRs and Triacs. Triacs are a useful alternative to relays for switching ac line voltages. The 2N6073A shown in Figure 27 is rated to handle 4 A (rms). The opto-isolated MOC3021 Triac shown features excellent electrical isolation from the noisy ac line and complete control over the high power Triac with only a few additional components. HEATING ELEMENT +5V 100 TMP12 NC = NO CONNECT 1 Figure 24. Driving a P-Channel MOSFET VREF TEMPERATURE VPTAT SENSOR & 8 VOLTAGE REFERENCE 2 1 VREF TEMPERATURE VPTAT SENSOR & 8 VOLTAGE REFERENCE 2 3 7 WINDOW COMPARATOR 7 V+ = 5V 300Ω NC 1 V+ 3 4.7kΩ WINDOW COMPARATOR 2 3 6 150Ω MOC3011 5 4 2N6073A NC 4 IRF130 5 +5V HYSTERESIS GENERATOR 2N1711 6 6 HEATING ELEMENT 4.7kΩ AC LOAD 100 TMP12 4 5 HYSTERESIS GENERATOR +5V NC = NO CONNECT 100 Figure 27. Controlling the 2N6073A Triac TMP12 Figure 25. Driving an N-Channel MOSFET Isolated Gate Bipolar Transistors (IGBTs) combine many of the benefits of power MOSFETs with bipolar transistors and are used for a variety of high power applications. Because IGBTs have a gate similar to MOSFETs, turning on and off the devices is relatively simple as shown in Figure 26. The turn on voltage for the IGBT shown (IRGB40S) is between 3.0 and 5.5 volts. This part has a continuous collector current rating of 50 A and a maximum collector to emitter voltage of 600 V, enabling it to work in very demanding applications. –12– REV. 0 TMP12 High Current Switching As mentioned earlier, internal dissipation due to large loads on the TMP12 outputs will cause some temperature error due to self-heating. External transistors buffer the load from the TMP12 so that virtually no power is dissipated in the internal transistors and minimal self-heating occurs. This section shows several examples using external transistors. The simplest case uses a single transistor on the output to invert the output signal is shown in Figure 28. When the open-collector of the TMP12 turns “ON” and pulls the output down, the external transistor Q1’s base will be pulled low, turning off the transistor. Another transistor can be added to re-invert the signal as shown in Figure 29. Now, when the output of the TMP12 is pulled down, the first transistor, Q1, turns off and its collector goes high, which turns Q2 on, pulling its collector low. Thus, the output taken from the collector of Q2 is identical to the output of the TMP12. By picking a transistor that can accommodate large amounts of current, many high power devices can be switched. 1 VREF TEMPERATURE VPTAT SENSOR & 8 VOLTAGE REFERENCE 2 3 4 7 WINDOW COMPARATOR 3 4 6 100 Figure 28. An External Transistor Minimizes Self-Heating +12V RELAY MOTOR SWITCH 3 4 4.7kΩ C 4.7kΩ TIP-110 2N1711 6 5 HYSTERESIS GENERATOR I V+ 7 WINDOW COMPARATOR +5V 100 TMP12 Figure 30. Darlington Transistor Can Handle Large Currents REV. 0 Q2 An example of a higher power transistor is a standard Darlington configuration as shown in Figure 30. The part chosen, TIP-110, can handle 2 A continuous which is more than enough to control many high power relays. In fact the Darlington itself can be used as the switch, similar to MOSFETs and IGBTs. Q1 2 Q1 Figure 29. Second Transistor Maintains Polarity of TMP12 Output C VREF TEMPERATURE VPTAT SENSOR & 8 VOLTAGE REFERENCE 2N1711 100 TMP12 1 C TMP12 5 HYSTERESIS GENERATOR I 4.7kΩ 4.7kΩ 5 HYSTERESIS GENERATOR 2N1711 6 V+ 2N1711 I 4.7kΩ VREF TEMPERATURE VPTAT SENSOR & 8 VOLTAGE REFERENCE 2 V+ 7 WINDOW COMPARATOR 1 –13– TMP12 OUTLINE DIMENSIONS Dimensions shown in inches and (mm). C2074-10-10/95 8-Pin Epoxy DIP 5 8 0.280 (7.11) 0.240 (6.10) 1 4 0.070 (1.77) 0.430 (10.92) 0.348 (8.84) 0.045 (1.15) 0.325 (8.25) 0.300 (7.62) 0.015 (0.381) TYP 0.210 (5.33) MAX 0.160 (4.06) 0.115 (2.93) 0.100 (2.54) 0.022 (0.558) 0.014 (0.356) 0.195 (4.95) 0.115 (2.93) 0.130 0.015 (0.381) (3.30) MIN 0.008 (0.204) SEATING PLANE 0°- 15° BSC 8-Pin SOIC 5 8 0.1574 (4.00) 0.1497 (3.80) 0.2440 (6.20) 0.2284 (5.80) 4 1 0.1968 (5.00) 0.1890 (4.80) 0.102 (2.59) 0.094 (2.39) 0.0196 (0.50) × 45° 0.0099 (0.25) 0.0098 (0.25) 0.0040 (0.10) 0°8° 0.0192 (0.49) SEATING 0.0138 (0.35) PLANE 0.0098 (0.25) 0.0075 (0.19) 0.0500 (1.27) 0.0160 (0.41) PRINTED IN U.S.A. 0.0500 (1.27) BSC –14– REV. 0