I'm building a 600v H-Bridge using IPZA60R060 MOSFETs together with isolated gate drivers UCC21520. I designed the PCB layout to be as tight as possible and thought I'd done a good job routing the gate drive signals. I've got a weird problem that I can't work out.
With NO load attached the MOSFETs are pulling a small current from the DC bus (about 20-30mA per half bridge). This only occurs when applying the 30KHz PWM signal from a STM32F407. With low bus voltages it doesn't matter much but I want this H-Bridge to operate at up to 450volts. At 75volts they're consuming about 2Watts and get hot. Weirdly, the current seems to stay 20-30mA regardless of the bus voltage.
- Increasing the deadtime both via hardware (resistor from DT pin of UCC21520) and via software. Nothing
- Removing the diode discharge resistor so the gate is charged and discharged via a 4.7R resistor - Nope
- Increasing this gate resistor to 10R then to 22R - No benefit
- Reducing the switching frequency from 42KHz to 20KHz did slightly reduce the current draw (30 -> 20mA)
I don't know what else to consider. The gate drive supply is provided by a separate 3S LiPo at 12v. Is it a layout problem or something to do with the separated kelvin gate/source pins? The circuit is no good to go to 450volts at the moment and I'm pulling my hair out!