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:
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:
Input Signal
Output Signal
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.
Hi Luke,
First off, sorry for the delay in responding to your query.
Here are a couple of comments/questions from our Apps team:
I am not sure why the customer used electrolytic capacitors for Clr_out and Ccp_out. The ceramic capacitors of appropriate voltage rating preferably with X7R dielectric would be a good choice for such applications. The electrolytic capacitors would be good choice for the bulk capacitor in the main battery/power line. Please see the schematic of our evaluation board.
It appears that the drain of the power stage is connected to a 10V supply, is this the same supply that is connected to Vcc? What is the current draw of the load? Is it possible that the load is causing the 12V 1W supply to overload.
To answer the questions about the ability to drive the load at 25kHz it is necessary to know what MOSFETs are being driven. Also, if the charge pump capacitors are not ceramic, then the specifications of the capacitors may reveal limitations to operation (a high ESR limits operation).
Are there decoupling capacitors on Vcc and Vcc2? If so, what is the value and type of capacitor? How does changing them affect the symptoms?
Best regards,
Tomas
