cancel
Showing results for 
Search instead for 
Did you mean: 

finding the cause for MOSFET burning STM32G431

ALedi.1
Associate III

Hey @ all

the setup:

  • custom motor control PCB
  • microcontroller: STM32G431CBU6
  • gate-driver: UCC2721, 15V
  • three shunt lowside current sense 150 µOhm
  • OPAMP MAXIM MAX40056 20V/V
  • inverter stage: 24x IRF7759 (4 parallel)
  • gate resistor 4,7 Ohm
  • gate-source resistor 20 kOhm each FET
  • motor: 48V, 3 PP, Rs = 4mOhm, Ls= 10 µH, BEMF 3,3 Vrms/kRPM, 200A DC max, 10.000 RPM max

Workbench settings:

0693W00000WHyo3QAD.png 

The motor runs fine even at 8000 RPM. The problem is that under small load of 2 kW (48V, 50 A DC, 4000 RPM), after 1-2 minutes of constant speed, a MOSFET burns through with an explosion, although the temperature at the inverter stage is only around 40°C and the FETs are cooled through a thermopad (1mm thick, 12 W/mK) and pressed onto a water cooled aluminium body. The cooling should be more than sufficient, as the same cooling system works fine on a motor controller from the competition with the same motor under full load (12 kW, 200 A DC) for 10 minutes and FET temperature <80°C.

I am trying to find the cause for the MOSFET burning. Could it be caused by bad current and flux PI regulator settings? The settings I use are automatically calculated parameters from the workbench, I didnt tune them myself and they can be seen in the screenshot above. The motor runs smooth though. I can provide a current reading of one of the OPAMP outsputs from the current measurement during operation (pink color):

0693W00000WHyuaQAD.png0693W00000WHyv4QAD.pngINFO: the huge voltage spikes during switching are caused by long measurement wires and are not "real".

Could any other wrongly-set parameter cause excessive heating or switching losses of the FETs that could lead to mosfet burning ?

Any suggestions are appreciated.

0 REPLIES 0