5 Use case No. 1: Bidirectional in-phase overcurrent detection

Figure 5-1 shows how AMC23C12 can be used for bidirectional in-phase overcurrent detection.

In a fully operational three-phase AC motor-drive system, the sum of three-phase current to the AC motor should be zero, regardless of braking or running conditions (that is, IA + IB + IC = 0).

Calculating the third-phase current in low- to mid-end motor drives from measured current on two phases can help reduce costs. I recommend monitoring the current on the third phase to detect any electrical fault events. While you could place a current sensor on the third phase with an isolated amplifier or isolated modulator, you could also use a reinforced isolated window comparator AMC23C12 for simplicity, cost-effectiveness and solution size. The AMC23C12offers bidirectional overcurrent detection with an integrated window comparator.

As shown in location 1 of Figure 5-1, a shunt resistor produces a voltage drop that the AMC23C12 reinforced window comparator senses. The AMC23C12 has an open-drain output, OUT, which actively pulls low when the input voltage exceeds the pre-defined threshold values of the voltage on the reference pin for the purposes of overcurrent detection. Figure 5-2 shows an overcurrent event output waveform.

For both overcurrent and short-circuit detection, you can use the AMC23C14 dual window comparator.