Precision Thermocouple Amplifiers
with Cold Junction Compensation
AD8494/AD8495/AD8496/AD8497
FEATURES
FUNCTIONAL BLOCK DIAGRAM
SENSE
Low cost and easy to use
AD8494/AD8495/
Pretrimmed for J or K type thermocouples
Internal cold junction compensation
High impedance differential input
Standalone 5 mV/°C thermometer
Reference pin allows offset adjustment
Thermocouple break detection
Laser wafer trimmed to 1°C initial accuracy
and 0.025°C/°C ambient temperature rejection
Low power: <1 mW at VS = 5 V
AD8496/AD8497
–IN
ESD AND
OVP
A2
1MΩ
COLD JUNCTION
COMPENSATION
THERMO-
COUPLE
A3
OUT
A1
+IN
ESD AND
OVP
Wide power supply range
Single supply: 2.7 V to 36 V
Dual supply: 2.7 V to 18 V
REF
Figure 1.
Small, 8-lead MSOP
APPLICATIONS
Table 1. Device Temperature Ranges
Optimized Temperature Range
J or K type thermocouple temperature measurement
Setpoint controller
Celsius thermometer
Universal cold junction compensator
White goods (oven, stove top) temperature measurements
Exhaust gas temperature sensing
Thermo-
couple
Part No. Type
Ambient Temperature Measurement
(Reference Junction) Junction
AD8494
AD8495
AD8496
AD8497
J
K
J
0°C to 50°C
0°C to 50°C
25°C to 100°C
25°C to 100°C
Full J type range
Full K type range
Full J type range
Full K type range
K
Catalytic converter temperature sensing
GENERAL DESCRIPTION
The AD8494/AD8495/AD8496/AD8497 are precision instrumen-
tation amplifiers with thermocouple cold junction compensators
on an integrated circuit. They produce a high level (5 mV/°C)
output directly from a thermocouple signal by combining an
ice point reference with a precalibrated amplifier. They can be
used as standalone thermometers or as switched output setpoint
controllers using either a fixed or remote setpoint control.
The AD8494/AD8495/AD8496/AD8497 allow a wide variety of
supply voltages. With a 5 V single supply, the 5 mV/°C output
allows the devices to cover nearly 1000 degrees of a thermo-
couple’s temperature range.
The AD8494/AD8495/AD8496/AD8497 work with 3 V supplies,
allowing them to interface directly to lower supply ADCs. They
can also work with supplies as large as 36 V in industrial systems
that require a wide common-mode input range.
The AD8494/AD8495/AD8496/AD8497 can be powered from a
single-ended supply (less than 3 V) and can measure temperatures
below 0°C by offsetting the reference input. To minimize self-
heating, an unloaded AD849x typically operates with a total
supply current of 180 μA, but it is also capable of delivering in
excess of 5 mA to a load.
PRODUCT HIGHLIGHTS
1. Complete, precision laser wafer trimmed thermocouple
signal conditioning system in a single IC package.
2. Flexible pinout provides for operation as a setpoint
controller or as a standalone Celsius thermometer.
3. Rugged inputs withstand 4 kV ESD and provide over-
voltage protection (OVP) up to VS 25 V.
4. Differential inputs reject common-mode noise on the
thermocouple leads.
5. Reference pin voltage can be offset to measure 0°C on
single supplies.
The AD8494 and AD8496 are precalibrated by laser wafer
trimming to match the characteristics of J type (iron-constantan)
thermocouples; the AD8495 and AD8497 are laser trimmed to
match the characteristics of K type (chromel-alumel) thermo-
couples. See Table 1 for the optimized ambient temperature
range of each part.
6. Available in a small, 8-lead MSOP that is fully RoHS compliant.
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 that may result from its use. Specifications subject to change without notice. No
license is granted by implication or otherwise under any patent or patent rights of Analog Devices.
Trademarks and registeredtrademarks arethe property of their respective owners.
One Technology Way, P.O. Box 9106, Norwood, MA 02062-9106, U.S.A.
Tel: 781.329.4700
Fax: 781.461.3113
www.analog.com
©2010 Analog Devices, Inc. All rights reserved.
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