ADT70

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+INIA INST AMP SHUT- DOWN GND SENSE OUT IA AGND DGND2VS SHUTDOWN +INOA 2INOA OUT OA +VS 2.5V REF IOUTA IOUTB MATCHED CURRENT SOURCES NULLA NULLB BIAS 2.5VREFOUT ADT70 PIN CONFIGURATIONS 20-Lead P-DIP (N Suffix) SHUTDOWN –VS +INOA –INOA VOUT OA +V S AGND VREFOUT BIAS VOUT IA DGND NULLA NULLB IOUTA IOUTB –INIA +INIA RGA RGB GND SENSE a ADT70 TOP VIEW (Not to Scale) 20-Lead SOIC (R Suffix) –VS +INOA –INOA VOUT OA +V S AGND VREFOUT BIAS VOUT IA DGND SHUTDOWNNULLA NULLB IOUTA IOUTB

2 INIA

1 INIA RGA

(Not to Scale) a 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 PRTD Conditioning Circuit and Temperature Controller ADT70*

FEATURES

PRTD Temperature Measurement Range Typical IC Measurement Error 618C Includes Two Matched Current Sources Rail-to-Rail Output Instrumentation Amp Uncommitted, Rail-to-Rail Output Op Amp On-Board 12.5 V Reference Temperature Coefficient 625 ppm/ 8C

15 V or 65 V Operation

APPLICATIONS

Temperature Acquisition Cards GENERAL DESCRIPTION The ADT70 provides excitation and signal conditioning for resistance-temperature devices (RTDs). It is ideally suited for 1 kW Platinum RTDs (PRTDs), allowing a very wide range of temperature measurement. It can also easily interface to 100 W PRTDs. Using a remote, low cost thin-film PRTD, the ADT70 can measure temperature in the range of –50 °C to +500°C. With high performance platinum elements, the temperature change can be extended to 1000 °C. Accuracy of the ADT70 and PRTD system over a –200 °C to +1000°C temperature range heavily depends on the quality of the PRTD. Typically the ADT70 will introduce an error of only – 1°C over the transducer's temperature range, and the error may be trimmed to zero at a single calibration point. The ADT70 consists of two matched 1 mA (nominal) current sources for transducer and reference resistor excitation, a preci- sion rail-to-rail output instrumentation amplifier, a 2.5 V refer- ence and an uncommitted rail-to-rail output op amp. The ADT70 includes a shutdown function for battery powered equipment, which reduces the quiescent current from 4 mA to less than 10␣mA. The ADT70 operates from either single +5 V or –5 V supplies. Gain or full-scale range for the PRTD and ADT70 system is set by a precision external resistor connected to the instrumentation amplifier. The uncommitted op amp may be used for scaling the internal voltage reference, providing a “PRTD open” signal or “over-temperature” warning, a heater switching signal, or other external conditioning determined by the user. The ADT70 is specified for operation from 240°C to 1125°C and is available in 20-lead DIP and SO packages. Patent pending. Tel: 781/329-4700 World Wide Web Site: http://www.analog.com Fax: 781/326-8703 © Analog Devices, Inc., 1998

Parameter Symbol Conditions Min Typ Max Units SYSTEM CONFIGURATION Gain R L = 1 kW 1.234 1.295 1.364 mV/ W Line Regulation –2.25 60.35 2.25 %/V CURRENT SOURCES Output Current I Q1, IQ2 RL = 1 kW 0.9 mA Output Current Mismatch I Q1 – IQ2 RL = 1 kW –2 60.5 2 mA Voltage Compliance –VS to +VS – 1.5 V INSTRUMENTATION AMP Input Offset Voltage V IOS –700 6150 700 mV TA = +25°C –500 6100 500 mV Output Offset Voltage V OOS –12 651 2 m V TA = +25°C– 7 637 m V Input Bias Current I B –75 640 75 nA TA = +25°C –60 630 60 nA Input Offset Current I OS –3 613 n A Common-Mode Rejection CMR V CM = 0.5 V to 3 V 65 85 dB Output Voltage Swing V OUT RL = ¥ , VS = 65 V –V S + 25 +V S – 25 mV VOLTAGE REFERENCE Output Voltage 2.485 2.5 2.515 V TA = +25°C 2.49 2.5 2.51 V Load Regulation I L = 0 mA to 1 mA 250 ppm/mA Temperature Coefficient 610 ppm/ °C Line Regulation + 4.5 V £ VS £ +5.5 V 675 ppm/V OPERATIONAL AMPLIFIER Input Offset Voltage V IOA –1,000 6400 1,000 mV TA = +25°C –800 6200 800 mV Input Offset Voltage Drift T CVIOA 1 mV/°C Input Bias Current I B –75 640 75 nA TA = +25°C –60 630 60 nA Input Offset Current I OS –3 613 n A Open-Loop Voltage Gain A VOL RL = ¥ 2V / mV Output Voltage Swing V OUTA RL = ¥ –VS + 10 +V S – 10 mV Common-Mode Rejection Ratio CMRR V CM = 1 V to 4 V 85 105 dB TA = +25°C 88 110 dB Power Supply Rejection Ratio PSRR 63 V £ VS £ 66 V 100 150 dB Slew Rate SR T A = +25°C, AV = 1, 0.17 V/ ms VIN = 0 V to 4 V SHUTDOWN INPUT Input Low Voltage V IL 0.8 V Input High Voltage V IH 2.4 V POWER SUPPLY Supply Current I SY RL = 1 kW 3.5 5 mA Shutdown Supply Current I SD 10 30 mA Supply Voltage V S +4.5 +5.5 V Dual Supply Voltage 64.5 65.5 V Specifications subject to change without notice. ADT70–SPECIFICATIONS REV. 0–2– (VS = 15 V, 2408C £ TA £ 11258C unless otherwise noted)

REV. 0 –3– ORDERING GUIDE Temperature Model Range Package ADT70GR 240°C to 1125°C 20-Lead SOIC ADT70GN 240°C to 1125°C 20-Lead PDIP ABSOLUTE MAXIMUM RATINGS* Storage Temperature Range Junction Temperature Range NOTE *Stresses above those listed under Absolute Maximum Ratings may cause perma- nent damage to the device. This is a stress rating only; functional operation of the device at these or any other conditions above those listed in the operational sections of this specification is not implied. Exposure to absolute maximum rating condi- tions for extended periods may affect device reliability. Package Type uJA* uJC Units 20-Lead SOIC (R) 74 24 °C/W 20-Lead PDIP (N) 102 31 °C/W NOTE *qJA is specified for device in socket/soldered on circuit board (worst case conditions). TRANSISTOR COUNT: 158 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 ADT70 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. WARNING! ESD SENSITIVE DEVICE

Figure 22. Op Amp CMRR vs. Frequency

2 PSRR

Figure 23. Op Amp PSRR vs. Frequency Figure 24. Op Amp Closed Loop Gain vs. Frequency Figure 19. In Amp PSRR vs. Frequency – A V = 1.4 Figure 20. In Amp PSRR vs. Frequency – A V = 14 Figure 21. In Amp Closed Loop Gain vs. Frequency

REV. 0 –9– would contribute to the difference in voltage drop between the RTD and the reference resistor. Thus, an error in reading the ac- tual temperature could occur. Table I. Copper Wire Gauge Size to Resistance Table. Lead-wire AWG Ohms/foot at +25ºC 12 0.0016 14 0.0026 16 0.0041 18 0.0065 20 0.0103 22 0.0162 24 0.0257 26 0.0413 28 0.0651 30 0.1027 From Table I the amount of lead-wire resistance effect in the circuit can be estimated. For example, connect 100 feet of AWG 22 wire to a 100 W Platinum RTD (PF element). The lead-wire resistance will be: R = 100 ft 3 0.0162 W /ft = 1.62 W . Thus the total resistance you have with the PRTD will be: RTOTAL . . =+ =100 1 62 101 62WW W Since the 100 W reference resistor is assumed to be relatively close to the ADT70, the lead-wire resistance is negligible. This shows 1.62 W of inaccuracy. From the PRTD’s data sheet, the PRTD’s sensitivity rating (W /°C) can be used with the lead-wire resistance to approximate the accuracy error in temperature degree (°C). Following the ex- ample above, the sensitivity of the 100 W PRTD is 0.385 W /°C (taken from PRTD data sheet). Hence the approximate error is: Error C C=° = °16 2 03 8 5 42 1. / . / .WW assuming the reference resistor is constant at 100 W throughout the temperature range. As shown above, this is a significant inaccuracy, especially for ap- plications where the PRTD would be hundreds of feet away from the ADT70. To reduce lead-wire error it is recommended to use a larger sensitivity RTD; 1 kW instead of 100 W . Furthermore, in the application circuit section, Figure 28 illustrates how to elimi- nate such error by using the part’s general purpose op amp. Self-Heating Effect Another contributor to measurement error is the self-heating ef- fect on the RTD. As with any resistive element, power is dissi- pated in an amount equal to the square of the excitation current times the resistance of the element. The error contribution of the heat generated by this power dissipation can easily be calculated. For example, if the package thermal resistance is 50°C/W, the RTD nominal resistance is 1 kW and the element is excited with a 1 mA current source, then the artificial increase in temperature (DºC) as a result of self-heating is: D° = ·CI R PACKAGE 0 q D° = () ·W · °Cm A C W1 1000 50 D° = °CC 00 5. where: uPACKAGE = thermal resistance of package R0 = value of RTD resistance

APPLICATION INFORMATION

As shown in Figure 27, using a 1 k W PRTD, 1 kW reference resistor, 49.9 kW resistor between RGA (Pin 11) and RGB (Pin 12), and shorting BIAS (Pin 4) with V REFOUT (Pin 3) together, the output of OUTIA (Pin 14) will have a transfer function of Vm V ROUT PRTD RESISTANCE REFERENCE RESISTANCE=W · ()1 299. / D - RGA RGB +INIA 2INIA INST AMP SHUT- DOWN GND SENSE OUT IA AGND DGND 2VS SHUTDO WN +INOA 2INOA OUT OA +V S 2.5V REF IOUTA IOUTB MATCHED CURRENT SOURCES NULLA NULLB BIAS 2.5VREFOUT ADT70 49.9kV VOUT @ 5mV/8C INDEPENDENT OP AMP 50kV +5V 1kV PRTD 1kV REF RESISTOR POTENTIOMETER IS USED TO ACHIEVE HIGHER PRECISION OF MATCHING CURRENT. 21V < 2VS < 25V Figure 27. Basic Operational Diagram

gain resistor using the following equation. and will turn on when SHUTDOWN pin becomes high (+V S). reference if different output current is preferred. mize the lead-wire resistance effect. input, there is no lead-wire resistance error. the reference resistor and the PRTD to minimize error. important issue is ensuring that the ADT70 is properly biased. Figure 28. 4-Wire Lead-Wire Resistance Cancellation Circuit

Figure 32. 100␣W 0.00385 PRTD Application Showing Figure 31. Single Supply Application with an ADR290 “Pseudo-Ground”

The majority of PRTD sensors use a scale factor of 0.00385 W /W /°C. Figure 33. Typical PRTD Application with American

0.003916 W / W /°C Scale; 1 kW Scale

Figure 34. Typical Strain Sensor Application (Two Element Varying) range. The sensor used in this circuit has two elements varying. circuits whether one-, two-, or all-element varying. plication requires only one current source.

REV. 0–14– OUTLINE DIMENSIONS Dimensions shown in inches and (mm). 20-Lead Plastic DIP (P-Suffix) 11 0 1.060 (26.90) 0.925 (23.50) 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 (8.25) 0.008 (0.204) 0.195 (4.95) 0.115 (2.93) 20-Lead SOIC (S-Suffix) SEATING PLANE 0.0118 (0.30) 0.0040 (0.10) 0.0192 (0.49) 0.0138 (0.35) 0.1043 (2.65) 0.0926 (2.35) 0.0500 (1.27) BSC 0.0125 (0.32) 0.0091 (0.23) 0.0500 (1.27) 0.0157 (0.40) 0.0291 (0.74) 0.0098 (0.25)x 45° 20 11 101 0.5118 (13.00) 0.4961 (12.60) 0.4193 (10.65) 0.3937 (10.00) 0.2992 (7.60) 0.2914 (7.40) PIN 1 C3395–8–7/98PRINTED IN U.S.A.