EVAL6498L High side problem

[ProgBoy]

Hi Everybody!

At this time I would like to use two EVAL6498L board for a DC brushed motor, (H-bridge setup).

Selected mosfet is: IRFZ34NPBF.

Selected PWM frequency: 20kHz width the STM32G431 MCU.

The PWM signals are generated on the GPIOs, and I’ve verified that they reach the driver’s HIN and LIN pins. The low-side MOSFETs switch correctly, but the high-side MOSFETs won’t turn on. The bootstrap capacitors are charged to about 12 V (measured directly across the capacitor leads). The control table is the following:

TIM1 ch	Driver Input	Forward	Revers
1	A LIN	Forced High	Forced Low
2	A HIN	Forced Low	PWM
3	B LIN	Forced Low	Forced High
4	B HIN	PWM	Forced Low

https://www.st.com/resource/en/data_brief/eval6498l.pdf

Added R4 and R7 with 10 Ω resistors.

What am I doing wrong?

[AScha.3 · Accepted solution]

Hi,

as this is a simple driver , needing/using bootstrap to load the hi-side....

you cannot have it switching the hi-side, while lo-side is not switching, = forced lo .

No more bootstrap loading...game over. Bootstrap cap is only loaded, when lo-side MOSFET is ON !

You have to switch a PWM always, hi and lo side , even if at 90/10 % , to keep the bootstrap cap re-loaded.

Or use a driver (as i do, in such case) with a separate isolated DC-DC converter, giving the hi side always power/voltage for gate driving.