UCC28782：About PWMH pulse skip

Hello,

Thanks for your interesting in TI's part.

Your waveforms shows the power stage already go through SBP, LPM,ABM and entry ABM to AAM boundary .

In ABM mode . the last PWMH pulse is missed , for example , if the PWML is three in a burst packet, PWMH will only has 2 pulse , if PWML is 2 pulses , only 1 PWMH pulse can be found. the last line waveforms in the excel file shows ABM to AAM mode transition is not smooth due to there is no enough hysteresis of BUR pin resistor setting . "Missing PWMH" in the waveform actually is two PWML pulses at ABM mode combine together , it looks like missed one PWMH pulse . We called it grouping pulse . it's a normal behavior for UCC28782 , but we can improve ABM to AAM mode transition to eliminate this symptom.

The method is increase hysteresis of AAM<==> ABM by increasing Rbur1 and Rbur2 at the same time , but keep the proportional not change . please make sure  Vbur2 - ▲Vbur(AAM) shown in below figure still higher than 0.7V.  (I think you already have UCC28782 calculator which can be down load from TI.COM website. page 3 "BUR Pin" )

Hello,

The latest waveforms shows  ABM -->AAM mode transition is smooth on your board after you changed the BUR pin resistors . but you still can see the PWMH issue. That is a different behavior with your previous waveform . We already fixed this issue in latest IC which will be soon released (within one month I think). so please apply some new samples after we release it . what you have tested is A version samples . the latest is AD version.

So please temporary ignore this issue and go ahead your debugging.

Thanks.