Application Note AN4304
This application note explains how to filter the input signal of a current sensing. The approach is especially useful for applications where the RF constraint is very important. A high-side current sensing can amplify input differential 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. In the TSC103, it can go even higher. The device amplifies small voltages across a shunt resistor on the high-voltage rail and feeds it to a low-voltage ADC which is generally embedded into a microcontroller. In many applications, the current-sense signal frequently needs to be filtered at the source, ie, across the sense resistor.
In an application such as a power supply or a DC-DC converter, the voltage output is generally noisy. Some spikes load the current. Alternatively, a temporary over voltage might occur creating either common mode or differential noise. Such high frequency signals may be demodulated by the current sensing device, resulting in an error in the current measurement.
Consequently, for power supply and DC-DC converter applic ations, it is necessary to filter the input path of the current sensing to improve the accuracy of the measurement. Such filters must be successfully implemented by choosing the right component values. If the wrong component values are selected, non - desire d offset voltages and gain errors might be introduced, which compromise circuit performance.
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Typical application schematic