Full J-Type Range 0° to 50° Thermocouple Amplifier w/Cold Junction Compensation

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 on the data sheet 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

* Complete, precision laser wafer trimmed thermocouple signal conditioning system in a single IC package.

* Flexible pinout provides for operation as a setpoint controller or as a standalone Celsius thermometer.

* Rugged inputs withstand 4 kV ESD and provide over-voltage protection (OVP) up to

VS ± 25 V.

* Differential inputs reject common-mode noise on the thermocouple leads.

* Reference pin voltage can be offset to measure 0°C on single supplies.

* Available in a small, 8-lead MSOP that is fully RoHS compliant.

Applications

* J 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

* Low cost and easy to use

* Pretrimmed for J type thermocouples

* Internal cold junction compensation

* High impedance differential input