Analog Devices AD595CQ, AD595CD, AD595AQ, AD595AD, AD595 Datasheet

Monolithic Thermocouple Amplifiers

a

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/ⴗC
Built-In Ice Point Compensation
Wide Power Supply Range: +5 V to ⴞ15 V
Low Power: <1 mW typical
Thermocouple Failure Alarm
Laser Wafer Trimmed to 1ⴗC 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 µA, 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

with Cold Junction Compensation

AD594/AD595

FUNCTIONAL BLOCK DIAGRAM

–IN –ALM +ALM V+ COMP VO FB

14 13 12 11 10 9 8

OVERLOAD
DETECT

AD594/AD595

G

1234567

+IN +C +T COM –T –C V–

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 cali­bration 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 control­ler 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.

+A

+TC

ICE
POINT
COMP.

–TC

G

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.

One Technology Way, P.O. Box 9106, Norwood, MA 02062-9106, U.S.A.
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Fax: [phone] © Analog Devices, Inc., 1999

(@ +25ⴗC and VS = 5 V, Type J (AD594), Type K (AD595) Thermocouple,

AD594/AD595–SPECIFICATIONS

Model AD594A AD594C AD595A AD595C

ABSOLUTE MAXIMUM RATING

to –V

+V

S

S

Common-Mode Input Voltage –V
Differential Input Voltage –V
Alarm Voltages

+ALM –V
–ALM –V

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°C
Stability vs. Temperature
Gain Error ⴞ1.5 ⴞ0.75 ⴞ1.5 ⴞ0.75 %
Nominal Transfer Function 10 10 10 10 mV/°C

AMPLIFIER CHARACTERISTICS

Closed Loop Gain

3

Input Offset Voltage (Temperature in °C) × (Temperature in °C) × (Temperature in °C) × (Temperature in °C) ×

Input Bias Current 0.1 0.1 0.1 0.1 µA
Differential Input Range –10 +50 –10 +50 –10 +50 mV
Common-Mode Range –V
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 –V
Single Supply 0 +V

Usable Output Current

4

3 dB Bandwidth 15 15 15 15 kHz

ALARM CHARACTERISTICS

V

at 2 mA 0.3 0.3 0.3 0.3 Volts

CE(SAT)

Leakage Current ⴞ1 ⴞ1 ⴞ1 ⴞ1 µA max
Operating Voltage at – ALM +V
Short Circuit Current 20 20 20 20 mA

POWER REQUIREMENTS

Specified Performance +V

5

Operating
Quiescent Current (No Load)

+V

S

–V

S

PACKAGE OPTION

TO-116 (D-14) AD594AD AD594CD AD595AD AD595CD
Cerdip (Q-14) AD594AQ AD594CQ AD595AQ AD595CQ

NOTES

1

Calibrated for minimum error at +25°C using a thermocouple sensitivity of 51.7 µV/°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.

2

Defined as the slope of the line connecting the AD594/AD595 errors measured at 0°C and 50°C ambient temperature.

3

Pin 8 shorted to Pin 9.

4

Current Sink Capability in single supply configuration is limited to current drawn to ground through a 50 kΩ 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 levels. 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

Min Typ Max Min Typ Max Min Typ Max Min Typ Max Units

36 36 36 36 Volts

– 0.15 +V

S

S

S

S

1

2

+V

–VS + 36 –V
+V

ⴞ3 ⴞ1 ⴞ3 ⴞ1 °C
ⴞ0.05 ⴞ0.025 ⴞ0.05 ⴞ0.025 °C/°C

–VS – 0.15 +V

S

–V

S

–V

S

S

S

S

193.4 193.4 247.3 247.3

51.70 µV/°C 51.70 µV/°C 40.44 µV/°C 40.44 µV/°C µV

– 0.15 –VS – 4 –VS – 0.15 –VS – 4 –VS – 0.15 –VS – 4 –VS – 0.15 –VS – 4 Volts

S

+ 2.5 +VS – 2 –VS + 2.5 +VS – 2 –VS + 2.5 +VS – 2 –VS + 2.5 +VS – 2 Volts

S

±5 ±5 ±5 ±5mA

= 5, –VS = 0 +VS = 5, –VS = 0 +VS = 5, –VS = 0 +VS = 5, –VS = 0 Volts

S

+VS to –V

– 2 0 –VS – 2 0 +VS + 2 0 +VS – 2 Volts

S

– 4 +VS – 4 +VS – 4 +VS – 4 Volts

S

≤ 30 +V

S

160 300 160 300 160 300 160 300 µA
100 100 100 100 µA

e.

unless otherwise noted)

S

+V

S

–VS + 36 –V
+V

S

to –V

≤ 30 +V

S

S

–VS – 0.15 +V
–V

–V

S

S

S

to –V

S

+V

–VS + 36 –V
+V

≤ 30 +V

S

–VS – 0.15 +V

S

–V

S

S

–V

S

S

S

+V

–VS + 36 Volts
+V

to –V

≤ 30 Volts

S

S

S

S

S

Volts
Volts

Volts

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 µV/°C, while for a type K it is 40.44 µV/°C. The resulting
gain for the AD594 is 193.4 (10 mV/°C divided by 51.7 µV/°C)
and for the AD595 is 247.3 (10 mV/°C divided by 40.44 µV/°C).

In addition, an absolute accuracy trim induces an input offset to

the output amplifier characteristic of 16 µV for the AD594 and
11 µV 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

–2–

compensated signal, the following transfer functions should be
used to determine the actual output voltages:

AD594 output = (Type J Voltage + 16 µV) × 193.4

AD595 output = (Type K Voltage + 11 µV) × 247.3 or conversely:

Type J voltage = (AD594 output/193.4) – 16 µV

Type K voltage = (AD595 output/247.3) – 11 µV

Table I lists the ideal AD594/AD595 output voltages as a func­tion 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

REV. C

AD594/AD595

Table I. Output Voltage vs. Thermocouple Temperature (Ambient +25°C, V

Thermocouple Type J AD594 Type K AD595
Temperature Voltage Output Voltage Output
°C mVmVmVmV

–200 –7.890 –1523 –5.891 –1454
–180 –7.402 –1428 –5.550 –1370
–160 –6.821 –1316 –5.141 –1269
–140 –6.159 –1188 –4.669 –1152
–120 –5.426 –1046 –4.138 –1021

–100 –4.632 –893 –3.553 –876

–80 –3.785 –729 –2.920 –719
–60 –2.892 –556 –2.243 –552
–40 –1.960 –376 –1.527 –375
–20 –.995 –189 –.777 –189

–10 –.501 –94 –.392 –94

0 0 3.1 0 2.7
10 .507 101 .397 101
20 1.019 200 .798 200
25 1.277 250 1.000 250

30 1.536 300 1.203 300
40 2.058 401 1.611 401
50 2.585 503 2.022 503
60 3.115 606 2.436 605
80 4.186 813 3.266 810

100 5.268 1022 4.095 1015
120 6.359 1233 4.919 1219
140 7.457 1445 5.733 1420
160 8.560 1659 6.539 1620
180 9.667 1873 7.338 1817

200 10.777 2087 8.137 2015
220 11.887 2302 8.938 2213
240 12.998 2517 9.745 2413
260 14.108 2732 10.560 2614
280 15.217 2946 11.381 2817

300 16.325 3160 12.207 3022
320 17.432 3374 13.039 3227
340 18.537 3588 13.874 3434
360 19.640 3801 14.712 3641
380 20.743 4015 15.552 3849

400 21.846 4228 16.395 4057
420 22.949 4441 17.241 4266
440 24.054 4655 18.088 4476
460 25.161 4869 18.938 4686
480 26.272 5084 19.788 4896

= –5 V, +15 V)

S

Thermocouple Type J AD594 Type K AD595
Temperature Voltage Output Voltage Output
°CmVmVmVmV

500 27.388 5300 20.640 5107
520 28.511 5517 21.493 5318
540 29.642 5736 22.346 5529
560 30.782 5956 23.198 5740
580 31.933 6179 24.050 5950

600 33.096 6404 24.902 6161
620 34.273 6632 25.751 6371
640 35.464 6862 26.599 6581
660 36.671 7095 27.445 6790
680 37.893 7332 28.288 6998

700 39.130 7571 29.128 7206
720 40.382 7813 29.965 7413
740 41.647 8058 30.799 7619
750 42.283 8181 31.214 7722
760 – – 31.629 7825

780 – – 32.455 8029
800 – – 33.277 8232
820 – – 34.095 8434
840 – – 34.909 8636
860 – – 35.718 8836

880 – – 36.524 9035
900 – – 37.325 9233
920 – – 38.122 9430
940 – – 38.915 9626
960 – – 39.703 9821

980 – – 40.488 10015
1000 – – 41.269 10209
1020 – – 42.045 10400
1040 – – 42.817 10591
1060 – – 43.585 10781

1080 – – 44.439 10970
1100 – – 45.108 11158
1120 – – 45.863 11345
1140 – – 46.612 11530
1160 – – 47.356 11714

1180 – – 48.095 11897
1200 – – 48.828 12078
1220 – – 49.555 12258
1240 – – 50.276 12436
1250 – – 50.633 12524

thermocouples Table I should not be used in conjunction with
European standard thermocouples. Instead the transfer function
given previously and a DIN thermocouple table should be used.

ICR-NI

ANSI type K and DIN N

CONSTANTAN
(ALUMEL)

IRON
(CHROMEL)

thermocouples are composed

+5V

13 12 11 10

14

AD594/
AD595

G

1234567

OVERLOAD
DETECT

+A

G

COMMON

+TC

10mV/8C

98

ICE

POINT

–TC

COMP.

Figure 1. Basic Connection, Single Supply Operation

of identical alloys and exhibit similar behavior. The upper tem­perature limits in Table I are those recommended for type J and
type K thermocouples by the majority of vendors.

REV. C

–3–

SINGLE AND DUAL SUPPLY CONNECTIONS

The AD594/AD595 is a completely self-contained thermocouple
conditioner. Using a single +5 V supply the interconnections
shown in Figure 1 will provide a direct output from a type J
thermocouple (AD594) or type K thermocouple (AD595) mea-

suring from 0°C to +300°C.

Any convenient supply voltage from +5 V to +30 V may be
used, with self-heating errors being minimized at lower supply
levels. In the single supply configuration the +5 V supply con­nects to Pin 11 with the V– connection at Pin 7 strapped to
power and signal common at Pin 4. The thermocouple wire in­puts connect to Pins 1 and 14 either directly from the measuring
point or through intervening connections of similar thermo­couple wire type. When the alarm output at Pin 13 is not used it
should be connected to common or –V. The precalibrated feed­back network at Pin 8 is tied to the output at Pin 9 to provide a

10 mV/°C nominal temperature transfer characteristic.

By using a wider ranging dual supply, as shown in Figure 2, the
AD594/AD595 can be interfaced to thermocouples measuring
both negative and extended positive temperatures.