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H-Bridge Predriver Unexpected Output

Question asked by Luke Barkley on Oct 26, 2017
Latest reply on Nov 9, 2017 by Tomas Vaverka

I am using the 33883 H-Bridge gate driver IC to drive a simple H4 bridge circuit which is connected identically to that in the application schematic (figure 14 ) the datasheet:

33883 H-Bridge Driver Circuit application schematic

I am switching at 25kHz using bipolar modulation and maintaining a duty cycle of 50 as it is being switched over a transformer. I am controlling the input signals with a STM32F4Discovery, which have an amplitude of 3V, which is sufficient according to the datasheet. Here are screenshots of both the input and output signals to HS1:

25kHz HS1 input signal at 3V

                                                                              Input Signal

GATE_HS1 output signal

                                                                               Output Signal

GATE_HS1 output signal zoomed                                                                               Output Signal Zoomed

You can see that it switches at the desired 25kHz for a short period of time before falling to zero and not switching again for another 3ms. I have used electrolytic capacitors for Clr_out and Ccp_out, but Ccp is a surface mount ceramic 33nF. Is there not enough charge stored in the capacitors to switch at the desired frequency? Is the 12VDC power supply which is rated at 1W not providing enough power to switch (33883 max power is 1.25W)?

 

Any help or suggestions would be greatly appreciated.

 

NB. Please ignore the pk-pk values on the oscilloscope, they are proportional to one another but not correct in amplitude.

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