I have designed an evaluation board with various modules. On one of the modules for the mosfet drivers I am using the MIC4609 IC. Now the IC seems to work OK until I put any sort of load on it, then the fault pin is pulled down and all the outputs are opened. The datasheet says the causes for the fault is ether a under voltage or over current. So the first thing I check is the supply voltage (12V) with a scope and ensure this does not drop with the fault pin. This turns out to be OK. Now the current pin looked to have a fair amount of motor noise on it, so just to prove concept I just shorted out the low pass cap on the ISNS pin to GND. I am still getting the fault and the bridge's disabling.
I have pretty much copied the reference design, but changed the bootstraps to 0.1uF (I am using very low gate charge mosfets), changed the gate resistors to 100Ohm, I only have a single shunt resistor for all three half bridges. I have monitored the current to ensure there are no current spikes (shoot through etc...).
I was having problems with very high current draw (and the buck current limiting decreasing the supply voltage below the threshold causing a fault). But once I put the reverse diodes on the gates this seemed to cure the problem and the supply voltage is now stable.
Does anyone have any idea (of have any good opinions) on what else could be causing the fault?