ADT14 Quad SetPoint, Programmable Temperature Monitor and Controller
Document overview
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Technical content
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. a ADT14 Tel: 617/329-4700 World Wide Web Site: http://www.analog.com Fax: 617/326-8703 © Analog Devices, Inc., 1997 Quad Setpoint, Programmable Temperature Monitor and Controller FUNCTIONAL BLOCK DIAGRAM VOLTAGE REFERENCE AND SENSOR CURRENT MIRROR WINDOW COMPARATORS HYSTERESIS VOLTAGE TEMPERATURE OUTPUT HYSTERESIS SETPOINT OUTPUT 1 SETPOINT OUTPUT 2 SETPOINT OUTPUT 3 SETPOINT OUTPUT 4 VPTAT 2.5V VREF SET 1 SET 2 SET 3 SET 4 GND ADT14 PIN CONFIGURATIONS DIP & SO TOP VIEW (Not to Scale) ADT14 NC = NO CONNECT OUTPUT 1 2.5V REFERENCE SETPOINT 4 OUTPUT 4 SETPOINT 1 NC NC SETPOINT 3 HYSTERESIS NCGROUND VPTAT SETPOINT 2 OUTPUT 2 OUTPUT 3
FEATURES
Four Programmable Temperature Setpoints Programmable Thermal Hysteresis Accuracy 638C Typ from –40 8C to +125 8C Temperature Output Scale Factor = 5 mV/K Resistor Programmable Temperature Setpoints 5 mA Open-Collector Setpoint Outputs Internal 2.5 V Reference 600 mA Max Quiescent Current at +5 V
APPLICATIONS
Power Supply Monitor and Control System Multiple Fan Controller System Workstation Thermal Management System GENERAL DESCRIPTION The ADT14 is a temperature sensor and controller that generates an output voltage proportional to temperature and provides four temperature trip points. The four trip points, or temperature setpoints, and their hysteresis are determined by voltage levels set by the user. An on-chip voltage reference provides an easy method for setting the temperature trip points. The ADT14 consists of a bandgap voltage reference combined with four matched comparators. The reference provides both a temperature-stable 2.5 V output, and a voltage proportional to absolute temperature (VPTAT) which has a precise temperature coefficient of 5 mV/K = 5 mV/( °C +273.15). The VPTAT out- put is nominally 1.49 V at +25 °C. The comparators determine whether the VPTAT output is above the voltages set up by external resistive dividers (temperature trip points) and generate an open-collector output signal when one of their respective thresholds has been exceeded. Hysteresis is programmed by a user-selected voltage at the hys- teresis pin. This voltage adjusts the hysteresis current which is used to generate a hysteresis offset voltage. The comparator’s noninverting inputs are connected in parallel, which guarantees that there is no hysteresis overlap and eliminates erratic transi- tions between adjacent trip zones. Using a proprietary thin-film resistor process in conjunction with production laser trimming, a temperature accuracy of ± 3°C at 25°C is guaranteed. The open-collector outputs are capable of sinking 5 mA, and provide TTL/CMOS logic compatibility with an external pull-up resistor. Operating from a single 5 V supply, the quiescent current is 600 µA max. The ADT14 is available in the 16-lead epoxy DIP and SO (small outline) packages.
Specifications subject to change without notice.
- Stresses above those listed under Absolute Maximum
- Digital inputs are protected; however, permanent damage
- Remove power before inserting or removing units from their
2N = Plastic DIP; R = Small Outline. Figure 1. Test Load
–3–REV. 0 WAFER TEST LIMITS Parameter Symbol Conditions Min Typ Max Units INPUTS SET HIGH, SET LOW Input Bias Current I B 70 nA OUTPUT VPTAT Temperature Accuracy T A = +25°C, No Load 1.5 °C OUTPUT VREF Nominal Value V REF TA = +25°C, No Load 2.490 2.510 V Line Regulation 4.5 V ≤ V ≤ 13.2 V ± 0.08 %/V Load Regulation 10 µA ≤ IVREF ≤ 500 µA ± 0.25 %/mA OPEN-COLLECTOR OUTPUTS OVER, UNDER Output Low Voltage V OL ISINK = 1.6 mA 0.4 V Output Leakage Current I OH 100 µA POWER SUPPLY Supply Range V+ 4.5 5.5 V Supply Current I SY Unloaded 600 µA NOTE Electrical tests are performed at wafer probe to the limits shown. Due to variations in assembly and nominal yield loss, yield after packaging is not guaranteed for standard product dice. Consult factory to negotiate specifications based on lot qualification through sample lot assembly and t esting. DICE CHARACTERISTICS Die Size 0.069 × 0.080 inch, 5520 sq. mils Transistor Count: 130 (V+ = +5 V, GND = 0 V, T A = +258C unless otherwise noted) WARNING! ESD SENSITIVE DEVICE 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 ADT14 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.
Figure 2. Thermal Time Constant in Forced Air
10 CHANGE IN TEMPERATURE – %
Figure 3. Thermal Response in Stirred Oil Bath Figure 4. Start-Up Voltage vs. Temperature Figure 5. Start-Up Response Figure 6. Accuracy Error vs. Temperature, Stirred Oil Bath Figure 7. Supply Current vs. Supply Voltage
Figure 14. ADT14 Setpoint Programming minimum recommended parallel ladder resistance is 12.5 k Ω . errors, choose 50 µA < IL < 200 µA. illustrates a single resistor ladder configuration.
50 A < IL < 200 A
Figure 15. Single Resistor Ladder fied voltage at the hysteresis pin (See Table I). Figure 16. ADT14 Hysteresis Profile
teresis current buffer is disabled. tiometer for fine adjustments. Figure 17. Hysteresis Connections for Miscellaneous effective setpoint divider ladder resistance to ground. tling time of five time constants, or six minutes, is necessary. supply bypassing is always recommended at the chip.
–8– REV. 0 Safety Considerations In heating and cooling system design, designers should antici- pate potential system fault conditions which may result in sig- nificant safety hazards which are outside the control of, and cannot be corrected by, the ADT14 based circuit. Governmen- tal 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 self- heating due to the power dissipated by the open-collector out- puts, which are capable of sinking 5 mA each continuously. Under full load, the ADT14 open-collector output device is dissipating, PDISS = 0.6V × 0.005 A× 4 = 12 mW which, in the small outline package, accounts for a temperature increase due to self-heating of ΔT = PDISS ×θ JA = 0.012 W × 81°C W = 0.97°C This will directly affect the accuracy of the ADT14 and will, for example, cause the device to switch the heating output off 0.97 degrees early. Alternatively, bonding the same package to a moderate heatsink limits the self-heating effect to approximately ΔT = PDISS ×θ JC = 0.012 W × 27°C W = 0.32°C which is a much more tolerable error in most systems. The V REF and VPTAT outputs are also capable of delivering sufficient current to contribute heating effects and should not be ignored. Buffering the Voltage Reference The reference output V REF is used to generate the temperature setpoint programming voltages for the ADT14. The onboard V REF output buffer is capable of 500 µA output drive into as much as a 50 pF load. Exceeding this load will affect the accu- racy of the reference voltage, will increase thermal errors due to internal heat generation, and may induce oscillations. External buffering of V REF with a low drift voltage follower will ensure optimal reference accuracy if a large load current is required. Amplifiers that offer low drift, low power consumption, and low cost appropriate to this application include the OP295 and members of the OP90, OP97, OP177 families, and others shown in the following applications circuits. With excellent drift and noise characteristics, V REF offers a good voltage reference for data acquisition and transducer excitation applications as well. Preserving Accuracy Over Wide Temperature Range Operation The ADT14 is unique in offering both a wide-range tempera- ture 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 ADT14 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 to minimize temperature 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 ADT14 requires a slightly different perspective regarding the thermal behavior of elec- tronic components. Thermal Response Time The time required for a temperature sensor to settle to a speci- fied 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 resistance is commonly specified in units of degrees per watt of power transferred across the thermal joint. Figure 3 illustrates the typical response to a step change in am- bient temperature for PDIP and SOIC packages. Thus, the time required for the ADT14 to settle to the desired accuracy is dependent on the package selected, the thermal contact estab- lished in the particular application, and the equivalent thermal conductivity of the heat source. For most applications, the set- tling time is probably best determined empirically. Switching Loads with the Open-Collector Outputs In many temperature sensing and control applications some type of switching is required. Whether it’s 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 ADT14 is accurately measuring temperature, the open- collector outputs should handle less than 5 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 power MOSFETs, thyristors, IGBTs, and Darlingtons. Figures 18a–18d show a variety of circuits where the ADT14 controls a switch. The main consideration in these circuits is the current required to activate the switch. Power FETs are popular for handling a variety of high current DC loads. Figure 18b shows the ADT14 driving a P-channel MOSFET transistor for a simple heater circuit. When the out- put 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 V GS, on the order of –2 V to –5 V is sufficient to turn on the device. Isolated Gate Bipolar Transistors (IGBT) 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 the devices on and off is relatively simple as shown in Figure 18c. 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. The last class of high power devices discussed here are thyris- tors, which include SCRs and triacs. Triacs are a useful alter- native to relays for switching ac line voltages. The 2N6073A shown in Figure 18d 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.
voltage on the receiving end. Figure 23. Temperature-to-Frequency Converter actually comes from the photodiode connected to Pins 3 to 4.
2.5 V reference voltage of the ADT14 for an accurate, low drift
accurate bias level at the receiving end. Figure 24. Isolation Amplifier
–16– REV. 0 C3067–12–5/97PRINTED IN U.S.A. OUTLINE DIMENSIONS Dimensions shown in inches and (mm). 16-Lead Plastic DIP (N-16) 0.840 (21.34) 0.745 (18.92) 0.280 (7.11) 0.240 (6.10) PIN 1 SEATING PLANE 0.022 (0.558) 0.014 (0.356) 0.060 (1.52) 0.015 (0.38) 0.210 (5.33) MAX 0.130 (3.30) MIN 0.070 (1.77) 0.045 (1.15) 0.100 (2.54) BSC 0.160 (4.06) 0.115 (2.93) 0.325 (8.26) 0.300 (7.62) 0.015 (0.381) 0.008 (0.204) 0.195 (4.95) 0.115 (2.93) 16-Lead Narrow-Body SOIC (R-16A) 16 9 0.3937 (10.00) 0.3859 (9.80) 0.2440 (6.20) 0.2284 (5.80) 0.1574 (4.00) 0.1497 (3.80) PIN 1 SEATING PLANE 0.0098 (0.25) 0.0040 (0.10) 0.0192 (0.49) 0.0138 (0.35) 0.0688 (1.75) 0.0532 (1.35) 0.0500 (1.27) BSC 0.0099 (0.25) 0.0075 (0.19) 0.0500 (1.27) 0.0160 (0.41) 0.0196 (0.50) 0.0099 (0.25)x 45°