9.2 Typical Application

9.2.1 Sensor Conditioning Circuit

Figure 9-6 shows a typical application for the INA849.

+

±

RG

RG

REF

1 k

1 k

INA849

10 k

0.1 …F

0.1 …F

OPA192

100 pF

100 k

100 k

5 V

0.1 …F

470 pF

470 pF

47 pF

+IN

íIN

Figure 9-6. Sensor Conditioning Circuit

9.2.1.1 Design Requirements

For the typical application, the design requirements are:

• AC-coupled input signal

– Capacitor tolerance of 5%

• Output range within 0 V to 5 V

• First-order filter stage with ‒3-dB frequency of 27 kHz

9.2.1.2 Detailed Design Procedure

If the instrumentation amplifier is used to drive ac-coupled input signals, an input bias current path must be

the resistor value, a trade-off must be made between input current noise that increases at lower values and input

voltage noise that increases at higher values.

Section 9.1.1 states that the reference pin must be connected to a low-impedance reference, as shown in the

application circuit example of the Sensor Conditioning Circuit. The reference pin must be connected to a 2.5-V

reference voltage established through a high-resistive divider. The OPA192 helps to buffer the reference voltage.

The effective output impedance of the OPA192 is derived as follows. The dc open-loop impedance of the

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INA849

SBOS945A – NOVEMBER 2020 – REVISED DECEMBER 2020

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