TPS54335A PWM waveform

Mark Pieper

Other Parts Discussed in Thread: TPS54335A

Hi,

I am investigating TPS54335A failures (lower FET failed short). We noticed that during discontinuous operation an extra brief HS switch event occurs. Please look at the below waveform. You will see that there is a brief HS FET on-event that happens away from the normal clock. Is this expected?

This picture shows that all of the "real" PWM events are in sync with the programmed clock frequency. Because this is in discontinuous mode there is some pulse skipping. The errant pulse is shown in both pictures and does not match the clock period. Do we understand this event?

Thanks,

Mark

over 9 years ago

0 Milo Zhu over 9 years ago

TI__Intellectual 2795 points

Please paste your schematic and test condition, will try to see if can repeat this behaivor to check what happened.

0 Mark Pieper over 9 years ago in reply to Milo Zhu

TI__Expert 4650 points

Here is their schematic. I think there might be a stability issue, which was causing the bursting shown above. The question of the spike is still open, though. The 24V rail is very stable. There is an additional 22uF elsewhere on the board, so tot Cout is around 69uF. "DNI" indicates a part that is not populated.

Power management

Power management forum

TPS54335A PWM waveform