Pretrimmed for Type J (AD594) or
Type K (AD595) Thermocouples
Can Be Used with Type T Thermocouple Inputs
Low Impedance Voltage Output: 10 mV/ C
Built-In Ice Point Compensation
Wide Power Supply Range: +5 V to 15 V
Low Power: <1 mW typical
Thermocouple Failure Alarm
Laser Wafer Trimmed to 1 C Calibration Accuracy
Setpoint Mode Operation
Self-Contained Celsius Thermometer Operation
High Impedance Differential Input
Side-Brazed DIP or Low Cost Cerdip
Monolithic Thermocouple Amplifiers
with Cold Junction Compensation
FUNCTIONAL BLOCK DIAGRAM
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
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
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
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.
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
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
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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.
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© Analog Devices, Inc., 1999