PCB shunt BLDC controller current sensing

Question

I am building an ESC. Motor: 22 V, max. current 90 A. Battery: max. current 60 A. My controller is a MIC4607.

The PWM frquency is 16 kHz, but I will try to get 20 kHz later.

As you see there is a RSNS resistor, which is connected to the source of the MOSFETs and to the MIC4607, where ILIM+ and ILIM- is a comparator which would trigger if the voltage rises above 200 mV and turn all high-side MOSFETs off. I want to use this function to protect my batteries and motor from overcurrent.

How do I do that? I would need a shunt resistor, but they are very bulky. I found SMD shunts that have 1 mΩ resistance and could withstand the current. P=I²·R would be 3.6 W. Is this possible? The voltage drop over it would be only 60 mV, but I could amplify it.

Another solution would be to measure the current at the battery with the current sensors of Alegro, up to 100 A bidirectional, and just apply a voltage to IlIM+ if the current excides the max. allowed current that would instantly switch off the MOSFETs.

Answer 1

With reference to the datasheet for the MIC4607, you can see that the current detected by Rsns is a latched fault current. This is the absolute maximum (peak) current at which you declare a fault, and all commutation stops.

If you want to set a LOWER trip point you can use the same Rsns that you have now and set your tripoint to accommodate your design but leaving the fault detection unaltered. There seems no need to provide another sense resistor, simply apply your desired external tripoint and logic functions to the voltage across Rsns.