OA1ZHA datasheet(24/35 Pages) STMICROELECTRONICS

24 / 35 page

Application information

OA1ZHA, OA2ZHA, OA4ZHA

24/35

DocID025994 Rev 2

5.11.2

Precision instrumentation amplifier

The instrumentation amplifier uses three op amp. The circuit, shown in Figure 48:

"Precision instrumentation amplifier schematic", exhibits high input impedance, so that the

source impedance of the connected sensor has no impact on the amplification.

Figure 48: Precision instrumentation amplifier schematic

The gain is set by tuning the Rg resistor. With R1 = R2 and R3 = R4, the output is given by

Equation 3.

Equation 3

The matching of R1, R2 and R3, R4 is important to ensure a good common mode rejection

ratio (CMR).

5.11.3

Low-side current sensing

Power management mechanisms are found in most electronic systems. Current sensing is

useful for protecting applications. The low-side current sensing method consists of placing

a sense resistor between the load and the circuit ground. The resulting voltage drop is

amplified using OA1ZHA, OA2ZHA and OA4ZHA CMOS op amp (see Figure 49: "Low-side

current sensing schematic").

Figure 49: Low-side current sensing schematic

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