TPS61261: Backfeeding boost converter with parallel source voltage

Andrew Mowry

Part Number: TPS61261

I have a design where I'd like to have a second (5V) power supply in parallel with the output of a boost converter (1.2V NiMH to 3.3V). The goal is to have either power source feed the device. Will the TPS61261 converter be harmed by backfeeding with 5V from USB? How about if I reduce the 5V to something slightly lower, say 4.5V, so it is well below the maximum voltage rating for all pins?

If this boost converter isn't the best choice for this application, could you suggest one that is? Or there a better best practice for this sort of dual-supply application? I'd rather not have to have a Schottky diode on the output of the boost converter because of the voltage drop.

Thanks!

over 1 year ago

0 Nathan Ding over 1 year ago

TI__Expert 7665 points

Hi Andrew,

Is TPS61261 used to boost from 1.2V to 3.3V?

If that, 5V will be fine for TPS61261, but there isn't any margin, so I think it would better if the voltage could be lower, like 4.5V.

Regards,

Nathan

0 Andrew Mowry over 1 year ago in reply to Nathan Ding

Prodigy 90 points

That's correct, I'm using it to boost from 1.2V to 3.3V. I need a protection diode on my 5V source anyway, so I could use a silicon diode with a forward voltage around 0.5V to bring it down to 4.5V. In case it sounds like I should be fine backfeeding the converter without needing to put it in shutdown mode, correct? Thanks for your help!

0 Andrew Mowry over 1 year ago in reply to Andrew Mowry

Prodigy 90 points

Sorry one more question to clarify: If I apply 4.5V to OUT when the device is not in shutdown mode, that 4.5V will not pass through to VIN, correct? There's an internal diode that prevents that?

0 Nathan Ding over 1 year ago in reply to Andrew Mowry

TI__Expert 7665 points

Hi Andrew,

Yes, 4.5V will be fine, and it will not pass through to VIN.

Regards,

Nathan

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TPS61261: Backfeeding boost converter with parallel source voltage