7.2.5 High-Voltage Instrumentation Amplifier

Differential measurements are common in a wide variety of applications. When high input impedance is

needed in a differential measurement, an instrumentation amplifier can be employed. The challenge is that

readily available, monolithic instrumentation amplifiers offer a limited input common-mode voltage range. Figure

7-6 shows a discrete instrumentation amplifier featuring the OPAx596. The circuit is valuable when a high

impedance, differential measurement is required in the presence of very high common-mode.

+

–

+

–

1k

499k

1k

499k

V

REF

V

IN

V

IN+

+60V

25V

+60V

25V

10m

Load

50V

OPA596

OPA596

1A

Figure 7-6. High-Voltage Instrumentation Amplifier

7.2.6 Composite Amplifier

The OPAx596 offers low input offset voltage and input offset drift. In some applications, however, even higher

precision is required. Figure 7-7 shows how to greatly improve the dc precision of the OPAx596. The OPA186

is a 24V, zero-drift op amps offered at a competitive cost and can be paired with the OPAx596 in a composite

amplifier configuration to create a high precision amplifier with high voltage output capability.

The first amplifier, OPA186, corrects the offset of the second amplifier, OPAx596. The gain of the composite

amplifier is set by RF and RG, such that the gain is equal to RF / RG + 1. In this application, the overall gain

of the circuit is 100V/V. Adding gain to the OPAx596 through R1 and R2 improves the overall bandwidth of

the composite amplifier by reducing the gain burden on the OPA186. Increasing the gain too much on the

second amplifier, however, reduces the closed loop bandwidth and can negatively affect phase margin. Special

considerations for stability are warranted when building composite amplifiers.

+

–

OPA186

12V

12V

100

+

–

OPA596

42.5V

99k

14k

1k

42.5V

1k

PDAC

100

V

OUT

AVDD

AVSS

1nF

Figure 7-7. High-Precision, High-Voltage Output Composite Amplifier

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OPA596, OPA2596

SBOSA42C – JUNE 2024 – REVISED DECEMBER 2025

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