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
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