Precision Thermocouple Amplifiers
with Cold Junction Compensation
AD8494/AD8495/AD8496/AD8497
Rev. C
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FEATURES
Low cost and easy to use
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 V
S
= 5 V
Wide power supply range
Single supply: 2.7 V to 36 V
Dual supply: ±2.7 V to ±18 V
Small, 8-lead MSOP
APPLICATIONS
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
Catalytic converter temperature sensing
FUNCTIONAL BLOCK DIAGRAM
–IN
+IN
OUT
REF
08529-001
A1
A2
AD8494/AD8495/
AD8496/AD8497
A3
SENSE
ESD AND
OVP
ESD AND
OVP
COLD JUNCTION
COMPENSATION
1MΩ
THERMO-
COUPLE
Figure 1.
Table 1. Device Temperature Ranges
Optimized Temperature Range
Part No.
Thermo-
Couple
Type
Ambient Temperature
(Reference Junction)
Measurement
Junction
AD8494 J 0°C to 50°C Full J type range
AD8495 K 0°C to 50°C Full K type range
AD8496 J 25°C to 100°C Full J type range
AD8497 K 25°C to 100°C Full K type range
GENERAL DESCRIPTION
The AD8494/AD8495/AD8496/AD8497 are precision
instrumentation 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 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.
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.
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.
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 V
S
± 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.
6. Available in a small, 8-lead MSOP that is fully RoHS compliant.
