half bridge/full bridge pwm

[richardb]

Hi 'm having small issue with A switching IC it's a hip4081a and there is an issue where is can blow itself up on start-up if its pins and brought up incorrectly. long story short...
i need to either use the clc's to invert the pwm output onto a different pin and also set both to low on startup

or

enable the half bridge mode for the pwm but i wasnt sure if there was a simple way to do this.


i have used half bridge mode before in a pic18f4550 but i'm now using(going to use)a pic18f27q43

do i need to use the 16bitpwm mode to do this?


Rich

[Jerry Messina]

The PWM peripheral has a lot more control than the CCP used in PWM mode. but you might look at the CWG (complimentary waveform generator).

In any case, if you need the IO pins to power up low you'll have to add pulldown resistors on the IO pins to keep the pins low during startup.
IO pins powerup as inputs, so they'll be floating until you get a chance to initialize them.

[Jerry Messina]

Looking at the HIP4081A datasheet, it has a DIS input that would help with initialization issues.
If you pull that high it should disable the outputs until you have set up the PWM outputs... tie that to an IO pin and set it low once everything is ready.

Both the PWM and CWG peripherals can generate complimentary signals, or as you mentioned you can use a CLC to invert the CCP PWM output.

[richardb]

yeah you think the disable input would be ideal and i was using it, but.......


there is an obscure Tb321 application note which suggests that you can get shoot-through faults. if you don't start with certain configurations.


although i'm starting to think that only applies to the original part. there is now an "A" variant which is what I am using.



Thanks for looking John.


Rich

[Jerry Messina]

I see. That app note would worry me... think I'd add the pulldown resistors to the ALI/BLI inputs to keep them low just in case.