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LM27762: Supply sequence using Pgood

JohnP

Intellectual 470 points

Part Number: LM27762

Dear Sir

I wish to use the LM27762 to power an RF amplifier which needs the negative supply up and running before the positive supply is applied. Can I use a logic inverter connected between the output of the Pgood pin to the positive enable pin to accomplish this requirement? It would seem as though this might work from examination of the Pgood truth table (Table 1 in the datasheet).

Thanks

John

over 7 years ago

0 JohnP over 7 years ago

Intellectual 470 points

or will it lead to an oscillating condition of Pgood high then low etc....

0 Chris Glaser over 7 years ago

TI__Guru**** 150760 points

Hi John,

This should work. Here is the EVM's startup with no glitch on PG when the positive rail turns on (after the negative one is already on).

CH1 = PG

CH2 = EN-

CH3 = +Vout

CH4 = EN+

Here is the -Vout starting and PG going low:

And here is the +Vout starting and PG staying low:

0 JohnP over 7 years ago in reply to Chris Glaser

Intellectual 470 points

Thanks a lot, I'll do a test board to try it.
Thanks
John