TPS22953 Power Good PG question

Ronnie Hughes

Other Parts Discussed in Thread: TPS22953

I have a TPS22953 circuit with an odd behavior on the PG falling edge. This is what the falling edge of the PG looks like:

I verified that Vin, Vbias, and PG pull-up voltage are all steady at 3.3V during this event. The output voltage of the switch is also steady and slowly ramping down.

This power down is triggered by the EN being pulled low. The EN signal looks good. When the PG goes down the voltage at the SNS pin is 0.59V, so it isn’t near the falling threshold. I failed to save the scope shot showing SNS and PG, but SNS was flat at 0.59V; I was looking to see if it dipped around or not and it wasn’t doing anything bad.

Here is a shot with EN (ch2) and PG (ch1).

The PG signal goes to a CPLD only, it isn’t ganged with anything else.

Here is the schematic:

What could be causing this behavior?

over 8 years ago

0 Aleksandras_Kaknevicius over 8 years ago

TI__Genius 15770 points

Hi Ronnie,

This behavior is sometimes seen due to the loading conditions of the TPS22953, but it will cause no issues for the device. If this noise is undesirable, you can find this recommendation from the datasheet:

"In systems that are very sensitive to noise or have long PG traces, it is recommended to add a small capacitance from PG to GND for decoupling."

A 0.1uF capacitance should smooth out the PG pin response.

Thanks,

Alek Kaknevicius

0 Janayya Hiremath over 8 years ago

TI__Prodigy 110 points

Hello Ronnie,

May I know in which simulator you tried to verify the PG behaviour?

Best Regards,
Janayya
Spice Modelling Engineer

0 Ronnie Hughes over 8 years ago in reply to Janayya Hiremath

TI__Expert 3090 points

There was no simulation effort. The waveforms shown are from physical hardware (customer's board). They will add a 0.1uF to PG pin as suggested above and see if that cleans up the falling edge.

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TPS22953 Power Good PG question