Hy there community,
I have the following setup: mosfets IRFP4468 (3 phase bridge), IR2110 fet driver, 22 ohm gate resistors, 3000uf +100nf caps on supply close to fets (fets 30v ,fet drivers are on 12v), atmega328 controlled; on power side 10sqmm cables , on command side 0.22 sqmm wires about 8cm long between gate drivers and fets (there is absolutely no way to shorted these wires).
Now the issue; there is ringing on the rising edge of the low side fet gates freq is about 20-23Mhz (low side pwm-ed, freq 16Khz) , only on the rising edge (for the length of the miller plateau, 600ns long) but not on the falling edge, now the ringing is constantly there when the duty cycle is small about 7us pulse, and the motor is not turning yet, as soon the motor starts to turn the ringing goes away but not all the time on some very few pulses there is but on most of others there is not; if i load the motor up to 6 amps, the ringing is more often about on half the pulses, if i disconnect the motor, ringing stops, if i put a 100ohm resistor in series with the motor (motor stopped) very small ringing.
I tried 50 ohm gate resistor almost no difference in ringing, i tried 1 ohm gate resistor small increase in ringing, i tried with 20cm wires between drivers and fets to see if wire length affects ringing but very small difference.
The probing was made with small ground lead (NOT the 3" crocodile terminated wire) directly on the fet gate , all three low side ring but none of the high side (high side have isolated supply, no bootstrap).
I read a ton about fets, watched almost every tutorial about fets and ringing, but i can not figure this behavior. Again i can not shorten (shorter than 7-8cm) the wires between drivers and fets.
I attached some snaps from oscilloscope sowing ringing and not ringing
