AD8497 AD [Analog Devices], AD8497 Datasheet - Page 14

• Manufacturer Part Number: AD8497
• Description: Precision Thermocouple Amplifiers with Cold Junction Compensation
• Manufacturer: AD [Analog Devices]

AD8494/AD8495/AD8496/AD8497
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.
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
supply voltages on +V
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.
V
1MΩ
THERMO-
OUT
COUPLE
= (T
Figure 33. Basic Connection for the AD849x
MJ
× 5 mV/°C) + V
+IN
–IN
S
and, if using dual supplies, on −V
8
1
COLD JUNCTION
COMPENSATION
REF
IN-AMP
2
REF
AD849x
–V
+V
S
3
S
5V
0.1µF
7
0.1µF
6
5
SENSE
OUT
10µF
10µF
S
, also.
Rev. 0 | Page 14 of 16
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
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.
V
OUT
= T
A
+IN
–IN
× 5 mV/°C
Figure 34. Ambient Temperature Sensor
8
1
COLD JUNCTION
COMPENSATION
REF
IN-AMP
2
AD849x
3
–V
5V
7
S
+V
S
6
5
SENSE
OUT