I am working with a "tried and true" H-Bridge MOSFET driver circuit. I have used this design 2 times before with no problems. Now I am having an issue that I cannot seem to solve. The only difference in the current iteration over the others is that my gate driver is 1.5" away from the MOSFET as opposed to 0.25" away. To compensate for this distance I am only running my PWM period at 16kHz instead of my usual 60-100kHz.
I am seeing a strange waveform on my high-side gate signal. After changing the capacitance of the bootstrap caps a higher value the period of the on-off problem goes up. A smaller value speeds up the period. My actual PWM duty and period are correct during this "on" time. It appears that the bootstrap caps are slowly loosing charge until the high side turns off to recharge and the process starts over. Aprox (800mV)
However if I use a super small capacitance the on-off pattern continues only to disrupt the actual PWM. I have check all of the microcontroller signals and they are perfectly clean and consistent.