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COMP. GG –TC +TC 1 2345 67 AD594/AD595 +IN +C +T COM –T –C V– –IN –ALM +ALM V+ COMP VO FB a Monolithic Thermocouple Amplifiers with Cold Junction Compensation AD594/AD595

FEATURES

Pretrimmed for Type J (AD594) or Type K (AD595) Thermocouples Can Be Used with Type T Thermocouple Inputs Low Impedance Voltage Output: 10 mV/ 8C Built-In Ice Point Compensation Wide Power Supply Range: +5 V to 615 V Low Power: <1 mW typical Thermocouple Failure Alarm Laser Wafer Trimmed to 1 8C Calibration Accuracy Setpoint Mode Operation Self-Contained Celsius Thermometer Operation High Impedance Differential Input Side-Brazed DIP or Low Cost Cerdip PRODUCT DESCRIPTION The AD594/AD595 is a complete instrumentation amplifier and thermocouple cold junction compensator on a monolithic chip. It combines an ice point reference with a precalibrated amplifier to produce a high level (10 mV/ °C) output directly from a ther- mocouple signal. Pin-strapping options allow it to be used as a linear amplifier-compensator or as a switched output setpoint controller using either fixed or remote setpoint control. It can be used to amplify its compensation voltage directly, thereby converting it to a stand-alone Celsius transducer with a low impedance voltage output. The AD594/AD595 includes a thermocouple failure alarm that indicates if one or both thermocouple leads become open. The alarm output has a flexible format which includes TTL drive capability. The AD594/AD595 can be powered from a single ended supply (including +5 V) and by including a negative supply, tempera- tures below 0°C can be measured. To minimize self-heating, an unloaded AD594/AD595 will typically operate with a total sup- ply current 160 mA, but is also capable of delivering in excess of – 5 mA to a load. The AD594 is precalibrated by laser wafer trimming to match the characteristic of type J (iron-constantan) thermocouples and the AD595 is laser trimmed for type K (chromel-alumel) inputs. The temperature transducer voltages and gain control resistors are available at the package pins so that the circuit can be recalibrated for the thermocouple types by the addition of two or three resistors. These terminals also allow more precise cali- bration for both thermocouple and thermometer applications. The AD594/AD595 is available in two performance grades. The C and the A versions have calibration accuracies of – 1°C and – 3°C, respectively. Both are designed to be used from 0 °C to +50°C, and are available in 14-pin, hermetically sealed, side- brazed ceramic DIPs as well as low cost cerdip packages. PRODUCT HIGHLIGHTS 1. The AD594/AD595 provides cold junction compensation, amplification, and an output buffer in a single IC package. 2. Compensation, zero, and scale factor are all precalibrated by laser wafer trimming (LWT) of each IC chip. 3. Flexible pinout provides for operation as a setpoint control- ler or a stand-alone temperature transducer calibrated in degrees Celsius. 4. Operation at remote application sites is facilitated by low quiescent current and a wide supply voltage range +5 V to dual supplies spanning 30 V. 5. Differential input rejects common-mode noise voltage on the thermocouple leads. REV. C 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. Tel: 781/329-4700 World Wide Web Site: http://www.analog.com Fax: 781/326-8703 © Analog Devices, Inc., 1999

AD594/AD595–SPECIFICATIONS REV. C–2– Model AD594A AD594C AD595A AD595C Min Typ Max Min Typ Max Min Typ Max Min Typ Max Units ABSOLUTE MAXIMUM RATING +VS to –VS 36 36 36 36 Volts Common-Mode Input Voltage –V S – 0.15 +V S –VS – 0.15 +V S –VS – 0.15 +V S –VS – 0.15 +V S Volts Differential Input Voltage –V S +VS –VS +VS –VS +VS –VS +VS Volts Alarm Voltages +ALM –V S –VS + 36 –V S –VS + 36 –V S –VS + 36 –V S –VS + 36 Volts –ALM –V S +VS –VS +VS –VS +VS –VS +VS Volts Operating Temperature Range –55 +125 –55 +125 –55 +125 –55 +125 °C Output Short Circuit to Common Indefinite Indefinite Indefinite Indefinite TEMPERATURE MEASUREMENT (Specified Temperature Range 0°C to +50°C) Calibration Error at +25 °C1 63 61 63 61 °C Gain Error 61.5 60.75 61.5 60.75 % Nominal Transfer Function 10 10 10 10 mV/ °C AMPLIFIER CHARACTERISTICS Closed Loop Gain 3 193.4 193.4 247.3 247.3 Input Offset Voltage (Tem perature in °C) · (Temperature in °C) · (Temperature in °C) · (Temperature in °C) · 51.70 mV/°C 51.70 mV/°C 40.44 mV/°C 40.44 mV/°C mV Input Bias Current 0.1 0.1 0.1 0.1 mA Differential Input Range –10 +50 –10 +50 –10 +50 mV Common-Mode Range –VS – 0.15 –V S – 4 –V S – 0.15 –V S – 4 –V S – 0.15 –V S – 4 –V S – 0.15 –V S – 4 Volts Common-Mode Sensitivity – RTO 10 10 10 10 mV/V Power Supply Sensitivity – RTO 10 10 10 10 mV/V Output Voltage Range Dual Supply –VS + 2.5 +V S – 2 –V S + 2.5 +V S – 2 –V S + 2.5 +V S – 2 –V S + 2.5 +V S – 2 Volts Single Supply 0 +V S – 2 0 –V S – 2 0 +V S + 2 0 +V S – 2 Volts Usable Output Current4 – 5 – 5 – 5 – 5m A 3 dB Bandwidth 15 15 15 15 kHz ALARM CHARACTERISTICS VCE(SAT) at 2 mA 0.3 0.3 0.3 0.3 Volts Leakage Current 61 61 61 61 mA max Operating Voltage at – ALM +VS – 4 +V S – 4 +V S – 4 +V S – 4 Volts Short Circuit Current 20 20 20 20 mA POWER REQUIREMENTS Specified Performance +V S = 5, –VS = 0 +V S = 5, –VS = 0 +V S = 5, –VS = 0 +V S = 5, –VS = 0 Volts Operating5 +V S to –VS £ 30 +V S to –VS £ 30 +V S to –VS £ 30 +V S to –VS £ 30 Volts Quiescent Current (No Load) +VS 160 300 160 300 160 300 160 300 mA –VS 100 100 100 100 mA PACKAGE OPTION TO-116 (D-14) AD594AD AD594CD AD595AD AD595CD Cerdip (Q-14) AD594AQ AD594CQ AD595AQ AD595CQ NOTES 1Calibrated for minimum error at +25 °C using a thermocouple sensitivity of 51.7 mV/°C. Since a J type thermocouple deviates from this straight line approximation, the AD594 will normally read 3.1 mV when the measuring junction is at 0 °C. The AD595 will similarly read 2.7 mV at 0 °C. 2Defined as the slope of the line connecting the AD594/AD595 errors measured at 0 °C and 50°C ambient temperature. 3Pin 8 shorted to Pin 9. 4Current Sink Capability in single supply configuration is limited to current drawn to ground through a 50 k W resistor at output voltages below 2.5 V. 5–VS must not exceed –16.5 V. Specifications shown in boldface are tested on all production units at final electrical test. Results from those tests are used to calculate outgoing quality l evels. All min and max specifications are guaranteed, although only those shown in boldface are tested on all production units. Specifications subject to change without notic e. (@ +258C and VS = 5 V, Type J (AD594), Type K (AD595) Thermocouple, unless otherwise noted) INTERPRETING AD594/AD595 OUTPUT VOLTAGES To achieve a temperature proportional output of 10 mV/ °C and accurately compensate for the reference junction over the rated operating range of the circuit, the AD594/AD595 is gain trimmed to match the transfer characteristic of J and K type thermocouples at 25°C. For a type J output in this temperature range the TC is 51.70 mV/°C, while for a type K it is 40.44 mV/°C. The resulting gain for the AD594 is 193.4 (10 mV/ °C divided by 51.7 mV/°C) and for the AD595 is 247.3 (10 mV/°C divided by 40.44 mV/°C). In addition, an absolute accuracy trim induces an input offset to the output amplifier characteristic of 16 mV for the AD594 and 11 mV for the AD595. This offset arises because the AD594/ AD595 is trimmed for a 250 mV output while applying a 25 °C thermocouple input. Because a thermocouple output voltage is nonlinear with respect to temperature, and the AD594/AD595 linearly amplifies the compensated signal, the following transfer functions should be used to determine the actual output voltages: AD594 output = (Type J Voltage + 16 mV) · 193.4 AD595 output = (Type K Voltage + 11 mV) · 247.3 or conversely: Type J voltage = (AD594 output/193.4) – 16 mV Type K voltage = (AD595 output/247.3) – 11 mV Table I lists the ideal AD594/AD595 output voltages as a func- tion of Celsius temperature for type J and K ANSI standard thermocouples, with the package and reference junction at 25°C. As is normally the case, these outputs are subject to cali- bration, gain and temperature sensitivity errors. Output values for intermediate temperatures can be interpolated, or calculated using the output equations and ANSI thermocouple voltage tables referred to zero degrees Celsius. Due to a slight variation in alloy content between ANSI type J and DIN F E-CUNI

given previously and a DIN thermocouple table should be used. Figure 1. Basic Connection, Single Supply Operation type K thermocouples by the majority of vendors. 10 mV/°C nominal temperature transfer characteristic. both negative and extended positive temperatures.

application is shown in Figure 10. which can be used as a buffer and/or inverter. Figure 10. Using the Alarm to Drive a TTL Gate drive an LED or other indicator as shown in Figure 11. Figure 11. Alarm Directly Drives LED of the thermal path to the environment and the alarm duration. driven from –ALM as shown in Figure 12. Figure 12. –ALM Driving A Negative Referenced Load volts below the V+ applied to the circuit. while connecting –IN to common provides an upscale output. thermometer as shown in Figure 13.

0 TO –15V

Figure 13. AD594/AD595 as a Stand-Alone Celsius