MOSFET driver problem with high-side fet

Thread Starter

Krzysztof Bieda

Joined Jan 5, 2016
Hello Everyone,

I have problem with IR2181 that runs in my motor controller.

On my microcontroller I set 4us deadTime ( PWM period is 50us).
Problem is with signal that goes to high-side fet gate from IR2181.
I have checked that with scope ( BLUE - microcontroller signal ( there is also logic buffer but signal there is identical), RED - highside fet gate):
Red signal "steps" are fluctuating and I also observe correct signal:

I do not know what is causing that high-side gate signal to fluctuate. I would like to know how to get rid off it, because it is causing short circuit:
Like here ( BLUE - low-side gate signal , RED - highside fet gate):

Has anyone knows how to eliminate that problem?

Best regards,

Thread Starter

Krzysztof Bieda

Joined Jan 5, 2016
That is the mistery I want to solve. On second scope pic it is correct like it should be.
That signal is fluctuating like sinewave. From correct to incorrect.


Joined Sep 17, 2013
The 'steps' in the gate signal correspond to the 4uS delays and should be present, although their shape and size will depend on the properties of the load that the FETs drive. If you are intermittently losing the steps, that suggests to me either the load characteristics aren't constant (quite likely if the load is a motor), or else there is a software glitch (unexpected interrupt?) in creating the Hin and Lin signals for the IR2181.