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Part Number: TIDM-1007
We are trying to cost down our GaN daughter cards to make our solution more competitive by changing isolated power supply on LMG3410-HB-EVM to bootstrap power supply.
When starting up, each low-side LMG3410 should be driven by a PWM with low duty cycle to charge up bootstrap cap of high-side LMG3410 and avoid inductor current saturation. High-side LMG3410 can't be switched correctly until corresponding fault signal set high.
So any clues on how we should modify the firmware of TIDM-1007 for bootstrap powered GaN daughter cards?
Thanks and Best Regards,
Please see the state machine of the PWM
// wait for positive zero crossing i.e. state 6
if(acSine < threshold_PZC2 && acSinePrev<0)
During startup, the lower FET switch is turned ON before upper switch , and it is soft started. so hopefully you do not need to do anything.
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In reply to Manish Bhardwaj:
Thanks for your reply!
I think the only problem left behind is that the voltage of bootstrap cap need to be charged higher than UVLO during soft-start. I'll put up some test on it.
As I look into state machine code of the PWM control, I get a bit confused. According to SLYT650 , the soft-start sequence of zero-crossing should be:
(1) All switches off => (2) Main FET soft-start => (3) Low freq FET on and sync FET soft-start => (4) Normal operation
Take positive zero-crossing for an example. Based on my understanding, positiveZeroCrossing1 and positiveZeroCrossing2 seems to be the same for (1) and main FET starts soft-switching during positiveZeroCrossing3, which doesn't fit the soft-start sequence.
So would you please share some more comments on how these 3 zero-crossing states work? I must get it wrong somewhere.
Thanks a lot!
In reply to Jingyuan Zhao1:
Hopefully the above diagram explains it a little better, during PZC3 state only the Low side high freq switch is ON. we did modify it slightly from the original proposal in the app note you referred to.
This diagram really helps a lot. I can fully understand the state machine now.
Thanks so much for all your time and help!
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