LP2992: Issue with on/off pin function

Nigel Evans

Part Number: LP2992

Hi,

I'm suddenly seeing strange behaviour on the LP2992 devices. Applying vinput of 3.7v , when on/off pin is tied low, device should be off right?

I'm getting 3.3v output no matter what I do with the on/off pin.

This is a circuit that's been used in a product which has been in the field for some time and not had this issue before.

Any tips?

Thanks

8 months ago

0 Nick Butts 8 months ago

TI__Mastermind 46425 points

I Nigel,

Yes, the device should be off if the ON/OFF pin is tied low. How is it tied low? Is there a possibility of it being above150mV? Is it a fixed 3.3V device?

Regards,

Nick

0 Nigel Evans 8 months ago in reply to Nick Butts

Prodigy 10 points

Hi Nick,

It's normally controlled by a GPIO and pulldown. Which used to work. I've even tried shorting direct to GND.

Yes, fixed output device.

Thanks,

Nigel

0 Nick Butts 8 months ago in reply to Nigel Evans

TI__Mastermind 46425 points

Hi Nigel,

Is it a 3.3V fixed device?

Thanks,

Nick

0 Nigel Evans 8 months ago in reply to Nick Butts

Prodigy 10 points

Hi Nick,

Yes, 3V3 fixed device

Thanks,

Nigel

0 Nick Butts 8 months ago in reply to Nigel Evans

TI__Mastermind 46425 points

Hi Nigel,

That's weird. Is the device sourcing any load? 3.7V -> 3.3V is within the range of the dropout spec depending on the loading condition so I wonder if the channel is damaged and it's just a coincidence that it looks like it's regulating to 3.3V. That would explain why ON/OFF has no effect. If you increase the input voltage up to say 4.5V does the output follow?

Can you share the schematic of the LP2992?

Thanks,

Nick

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LP2992: Issue with on/off pin function