BQ25895: BQ25895 PMID to VBUS?

Iain_Henderson

Part Number: BQ25895
Other Parts Discussed in Thread: BQ25890, BQ25896, BQ25985

Hi,

I have a question about the BQ25895's USB OTG boost mode.

In the datasheet, the OTG boost mode seems to produce the OTG voltage from the PMID pin, instead of directly out of the main VBUS pin as I would have expected from a USB charger IC with OTG functionality.

My question in, is there a way to configure this device so that this does happen, i.e. this:

This is because I have only one USB port (USB type C) and I want this to be used for both charging and as a source, depending on what is plugged into it.

To put in another way, is it possible to enable RBFET (Q1) when in OTG mode so that the OTG voltage is present at VBUS?

Thanks,

Iain.

over 5 years ago

0 Ning T over 5 years ago

TI__Guru 57321 points

Lain,

Please use pin-2-pin BQ25890 instead. Both PMID and VBUS are OTG outputs.

Thanks,

Ning.

0 Iain_Henderson over 5 years ago in reply to Ning T

Prodigy 180 points

Hey Ning,

Thanks for getting back to me and for the suggestion.

Unfortunately, the BQ25890 won't work for my application, because I need my OTG output to be capable of 3A, whereas the BQ25890 is only capable of 2.4A according to the datasheet.

Do you have any other suggestions? It seems strange that the BQ25895 isn't capable of providing USB OTG power to its main USB port? Once the device is in OTG mode, if I was to send PMID voltage to VBUS would it cause problems? Or can I manually enable the internal RBFET?

Thanks,

Iain.

0 Ning T over 5 years ago in reply to Iain_Henderson

TI__Guru 57321 points

Lain,

RBFET can not be controlled externally. You may add an external controllable "RBFET" circuitry for BQ25895.

Thanks,

Ning.

0 Betty Guo over 5 years ago in reply to Ning T

TI__Expert 7300 points

Hi Ning,

I have the same quetion about the VBUS voltage in OTG.

In the 19 page of BQ25895 datasheet show that:

During boost mode, the status register VBUS_STAT bits is set to 111, the VBUS output is 5V by default
(selectable via BOOSTV register bits). The boost output is maintained when BAT is above VOTG_BAT threshold

now, measure the PMIC voltage is 5.1V but the VBUS is 0V. It is different with the datasheet. could you help clarify why the VBUS is 0V? and how to get 5V in VBUS in the OTG mode?

I also find this E2E question:https://e2e.ti.com/support/power-management/f/196/p/838415/3100662?tisearch=e2e-sitesearch&keymatch=BQ25895%2525252525252520OTG#3100662

say, if need the OTG output at VBUS, can use BQ25896, does it mean the BQ25985 can't output to VBUS with OTG?

thanks.

0 Iain_Henderson over 5 years ago in reply to Ning T

Prodigy 180 points

Hey Ning,

I see, thanks for explaining. Is there no adverse effects of essentially supply 5V into VBUS when the device is in OTG mode?

Thanks,

Iain.

0 Ning T over 5 years ago in reply to Iain_Henderson

TI__Guru 57321 points

Lain,

For BQ25895, when applying 5V at VBUS, the device exits OTG automatically.

Thanks,

Ning.

0 Iain_Henderson over 5 years ago in reply to Ning T

Prodigy 180 points

Hey Ning,

Thanks for the reply. I don't quite understand this - above you said that I could add my own RBFET circuitry to connect PMID to VBUS in OTG mode so that I can supply the OTG voltage out of my main USB port? But based on your latest reply, doing so would mean that the VBUS pin would see this OTG voltage and therefore exit OTG mode... so the output at PMID would cease?

Would I therefore have to also implement another FET to block PMID voltage being seen at the VBUS pin?

If so this seems like a lot of extra components and complexity, I'll find another way.

Thanks,

Iain.

0 Ning T over 5 years ago in reply to Iain_Henderson

TI__Guru 57321 points

Lain,

You need to add external controllable switch to feed OTG output to USB without connecting to the VBUS pin. It should not be simple.

Thanks,

Ning.

Power management

Power management forum

BQ25895: BQ25895 PMID to VBUS?