November 2013

DocID025335 Rev 1

1/14

www.st.com

AN4369

Application note

Adjustable gain with a current sensing

Nicolas Aupetit

Introduction

This application note explains how to use current sensing amplifiers with series resistors on the sense

inputs. This approach is especially useful for applications where the gain must be adjusted.

When the current sensing amplifier is powered from a single-supply, Vcc = 5 V, it can amplify differential

input signals at a common-mode voltage well beyond the power supply rail. This common-mode

voltage, in a current-sense amplifier such as the TSC101, can rise to 28 V and can rise even higher in

the TSC103. The device amplifies small voltages across a shunt resistor on the high-voltage rail and

feeds it to a low-voltage ADC generally embedded in a microcontroller. The output voltage is

proportional to the voltage drop measured on the sense resistor.

The current sensing of the TSC series has a dedicated fixed gain that can be 20 V/V, 25 V/V, 50 V/V, or

100 V/V. The gain is given by the ratio R3/R1.

Figure 1 illustrates a typical application schematic.

Figure 1: Typical application schematic