We are currently developing a 3-phase BLDC motor driver using MSP6531 as gate driver.
However, the issue we encountering is that the motor triggers the OCP protection of the MPS6531 as soon as it starts.
1.We attemped to short the Rsense R5 directly to ground, but the protection was still triggered. The protection is only avoided when OC_REF pin is directly connected to GND.
2.The protection is particularly prone to occuring during startup; once the motor is running, the issue no longer occurs.
3.Using a current meter, the measured peak current did not exceed 10A, ruling out the possibility of MOSFET shoot-through.
4.The Vg signal of Q1 and Q2 were probed, and the waveforms are as follows. Severe ringing is observed during startup.
ch1: Vg of Q2
ch3: Vg of Q1
ch4: Vs of Q1
reference schematic
Please provide us with some suggestions
Regards
Hello Paul,
I wonder if the high ringing that you see upon startup of Q1 and Q2 would be due in part to excess parasitic inductance given the sudden di/dt change.
If your trace connecting these FETs is too long, this could likely be the issue. If you can minimize these traces this would be ideal.
You could also reduce this ringing by adding a small series gate resistor in order to slow charge/discharge, therefore damping oscillations. You could also use either a snubber circuit to absorb the ringing energy upon startup (but this would treat the symptom and not the root cause).
Hope this provided some insight.
Best,
Krishan
1 Like
Thank you so much, I was about to ask same question but you saved my day.
Startup VDS protection on the MP6531 is often triggered by switching transients or incomplete MOSFET turn-on rather than a real fault. If the bootstrap or VREG capacitors are undersized, the gate may not fully drive, causing a false VDS event. Careful layout and stable reference design also matter; adding TL431AFDT in feedback paths can help improve voltage stability in such circuits.
I’m glad you found this response helpful. Keep us updated on what you end up implementing and a performance update on the ringing of those FETs.
