BQ25792: USB OTG used as power backup

M Leeters

Part Number: BQ25792
Other Parts Discussed in Thread: BQ25798

Hi,

I'm looking into the BQ25792, we are developing a battery pack which is used as power source when the mains power is disconnected.

The mains power is used to charge the battery pack and powers the rest of the system.

When I read the datasheet I don't see anything about if it is possible to always go into OTG mode when the input power is disabled with changing any settings.

I only see the EN-OTG bit which can be set to change to OTG mode after 5ms, but does this always happen even if the VBUS voltage drops (mains power disconnected).

And when the EN-OTG bit is set that when there is voltage on the VBUS pin that is still charges the battery.

Thank you for your support!

over 2 years ago

+1 Jeff F over 2 years ago

TI__Guru**** 166626 points

Hi M,

I recommend that you look at the BQ25798 which has backup mode. Backup mode is simply OTG mode that turns on automatically when input power droops and provides the OTG output back to PMID pin not VBUS pin (like BQ25792).

Regards,

Jeff

0 M Leeters over 2 years ago in reply to Jeff F

Prodigy 20 points

Hi Jeff,

Thanks! That is indeed what I'm looking for. Do you know the switching time from the input to the battery?

Worst case we will need around 2A of current for the system.

Kind regards

0 Jeff F over 2 years ago in reply to M Leeters

TI__Guru**** 166626 points

Hi M,

With the recommended 66uF additional capacitance on PMID and auto backup trigger voltage set to 7.6V after VBUS=9V is removed, the PMID response for 2A load is shown in pink below ~82us for full settling to VPMID=9V reg voltage.

Regards,

Jeff

0 M Leeters over 2 years ago in reply to Jeff F

Prodigy 20 points

Thanks! That picture exactly what I mean.

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BQ25792: USB OTG used as power backup