AD8494/AD8495/AD8496/AD8497

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APPLICATIONS INFORMATION

BASIC CONNECTION

Figure 33 shows an example of a basic connection for the

AD849x, with a J type or K type thermocouple input.

IN-AMP

AD849x

OUT

SENSE

REF

0.1µF

10µF

5V

COLD JUNCTION

COMPENSATION

2

3

6

7

5

+IN

THERMO-

COUPLE

–IN

1M

Ω

8

1

0.1µF

10µF

Figure 33. Basic Connection for the AD849x

To measure negative temperatures, apply a voltage at the refer-

ence pin to offset the output voltage at 0°C. The output voltage

of the AD849x is

A filter at the input is recommended to remove high frequency

noise. The 1 MΩ resistor to ground enables open thermocouple

detection and proper grounding of the thermocouple. The sense

pin should be connected to the output pin of the AD849x.

Decoupling capacitors should be used to ensure clean power

A 0.1 μF capacitor should be placed as close as possible to each

AD849x supply pin. A 10 μF tantalum capacitor can be used

farther away from the part and can be shared.

AMBIENT TEMPERATURE SENSOR

The AD849x can be configured as a standalone Celsius thermo-

meter with a 5 mV/°C output, as shown in Figure 34. The

thermocouple sensing functionality is disabled by shorting both

AD849x inputs to ground; the AD849x simply outputs the value

from the on-board temperature sensor.

As a temperature sensor, the AD8494 has a measurement temp-

erature range of −40°C to +125°C with a precision output of

IN-AMP

AD849x

+IN

–IN

OUT

SENSE

REF

5V

COLD JUNCTION

COMPENSATION

8

2

3

6

7

1

5

Figure 34. Ambient Temperature Sensor

The AD8494 is the best choice for use as an ambient temper-

ature sensor. The AD8495, AD8496, and AD8497 can also be

configured as ambient temperature sensors, but their output

transfer functions are not precisely 5 mV/°C. For information

about the exact transfer functions of the AD8494/AD8495/

AD8496/AD8497, see the product page for the AD8494,

AD8495, AD8496, or AD8497, or contact an Analog Devices

representative.

The thermometer mode can be particularly useful for debugging

a misbehaving circuit. If the basic connection is not working,

disconnect the thermocouple and short both inputs to ground.

If the system reads the ambient temperature correctly, the

problem is related to the thermocouple. If the system does not

read the ambient temperature correctly, the problem is with

the AD849x or with the downstream circuitry.