I have a TPS3514 in a non-mains, low-voltage, "safe" bench-evaluation situation. In other words, no PFC or HV-to-12V Switcher is actually used. A 12V-5V0/3V3 follow-on switcher is used - but never gets to work as the FPO_ doesn't stay low - for long enough. I can hold FPO_ low and everything works - including PGO.
Here's my issue.
I set PSON_ (active low) low and 38ms later, FPO_ goes low (as it should). It should go low AND STAY LOW - while the PFC and Converter become operational. Only 300ms after it senses the last of 3V3, 5V0, 12V and PGI going high - could it decide to shut-down (implied from the timing diagram).
However, what I get out of FPO_ are sharp, poorly defined (possibly glitches) low pulses (spikes) that are about 20us wide. These repeat every 10ms. They start 38ms after PSON_ goes low and stop about 650ms later. As they are so short, there is no way they can turn-on any converter stage.
I'm sure that it must be a premature timing problem - as in possibly 3V3, 5V0, 12V or PGI are "coming alive" too-fast. However the data sheet is not giving me an idea as to what is happening. It is as though some condition keeps reseting the start-up process.
Any ideas as to what is happening?
