OA1ZHA Datasheet, PDF (24/35 Pages) STMicroelectronics – Fitness and healthcare

Application information
OA1ZHA, OA2ZHA, OA4ZHA
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
5.11.3
The matching of R1, R2 and R3, R4 is important to ensure a good common mode rejection
ratio (CMR).
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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