TPS62869: PG signal open drain cannot be used for sequencing?

Arnav Shah

Prodigy 100 points

Part Number: TPS62869

Hello,

I noticed that the PG signal for TPS62869 is open-drain. The data sheet says its good for sequencing:

"The PG signal can be used for sequencing of multiple rails by connecting it to the EN pin of other converters."

But how? It requires a pull-up which will automatically enable the next rail. How is this useful?

Thanks,

Arnav

over 2 years ago

+1 Chris Glaser over 2 years ago

TI__Guru*** 148630 points

Hi Arnav,

Section 2 in this app note shows a basic sequencing circuit: https://www.ti.com/lit/an/slva470a/slva470a.pdf PG is held low, which keeps the second device off until the first rail is in regulation.

Does that help?

Chris

0 Arnav Shah over 2 years ago in reply to Chris Glaser

Prodigy 100 points

Thanks for the app note; yes my mistake is connecting PG pullup to another voltage instead of Vout.

0 Arnav Shah over 2 years ago in reply to Arnav Shah

Prodigy 100 points

BTW this only works if Vout1 is sufficiently high. What if I use <1V vout, then this sequence won't work. The logic high is 0.8V, how can this work?

0 Chris Glaser over 2 years ago in reply to Arnav Shah

TI__Guru*** 148630 points

Hi Arnav,

You don't have to pull up PG to Vout. You can pull it up to Vin or a system I/O rail, such as 3.3V or 1.8V.

Chris

0 Arnav Shah over 2 years ago in reply to Chris Glaser

Prodigy 100 points

Hi Chris,

If you pull up to Vin then the EN line will be high before the PG signal can pull low. That is my original problem.

Thanks,

Arnav

0 Chris Glaser over 2 years ago in reply to Arnav Shah

TI__Guru*** 148630 points

Thanks for clarifying.

The device holds PG low when it is off. See Table 8-4 in the D/S. It is low until its output voltage is in regulation, and then it floats high.

Does it make sense?

Chris

0 Arnav Shah over 2 years ago in reply to Chris Glaser

Prodigy 100 points

Yes makes sense, thanks for clarifying.

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TPS62869: PG signal open drain cannot be used for sequencing?