AD8230

Rev. 0 | Page 12 of 16

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6

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AD8230

0.1

µF

0.1

µF

10

µF

10

µF

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AD8230

0.1

µF

0.1

µF

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AD8230

0.1

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0.1

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AD8230

0.1

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0.1

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AD8230

0.1

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0.1

µF

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µF

1

µF

1

µF

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µF

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AD8230

0.1

µF

0.1

µF

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AD8230

0.1

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0.1

µF

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AD8230

0.1

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0.1

µF

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AD8230

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LAYOUT

draws current to set the internal voltage references. In

be star-connected to ground (or to a reference voltage). In

APPLICATIONS

2

6

1

7

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3

AD8230

0.1

µF

200

Ω

19.1k

Ω

TYPE J

THERMOCOUPLE

1

µF

BAV199

1nF

1nF

4.99k

Ω

4.99k

Ω

100M

Ω

100M

Ω

BAV199

0.1

µF

Figure 34. Type J Thermocouple with Overvoltage Protection and RFI Filter

The AD8230 may be used in thermocouple applications, as

shown in Figure 2 and Figure 34. Figure 34 is an example of

such a circuit for use in an industrial environment. It has

voltage overload protection (see the Input Protection section

for more information) and an RFI filter in front. The matched

100 MΩ resistors serve to provide input bias current to the

input transistors and also serve as an indicator as to when the

thermocouple connection is broken. Well-matched 1% 4.99 kΩ

resistors are used in the RFI filter. It is good practice to match

the source impedances to ensure high CMR. The circuit is

configured for a gain of 193, which provides an overall

temperature sensitivity of 10 mV/°C.

2

6

1

7

5

8

4

3

AD8230

0.1

µF

1k

Ω

102k

Ω

350

Ω

350

Ω

350

Ω

350

Ω

4k

Ω

1

µF

0.1

µF

Figure 35. Bridge Measurement with Filtered Output

Measuring load cells in industrial environments can be a

challenge. Often, the load cell is located some distance away

from the instrumentation amplifier. The common-mode

potential can be several volts, exceeding the common-mode

input range of many 5 V auto-zero instrumentation amplifiers.

Fortunately, the AD8230’s wide common-mode input voltage

range spans 16 V, relieving designers of having to worry about

the common-mode range.