STPMIC1 PWR_USB_SW with 5V input

[PGE]

Dear all,

We are designing a board using STM32MP1 and STPMIC1 mostly as recommended in datasheet and application note. As we have a wide VIN range we added a discrete DC/DC with a 5V output that supply STPMIC1 VIN.

We would like to use STMPIC1 PWR_USB_SW as a power switch for USB. We understand that as we have a fixed 5V VIN we don't need BOOST features and we can use the BOOST bybass mode from VIN.

In some ST document we can read: "If PWR_USB_SW is used, the BOOST converter must be supplied, since the BOOST output is used as PWR_USB_SW input"

At the end it's not clear, do we really need to power VLXBST and add an inductor even if we only need the the bypass mode and no boost function ?

Thanks in advance for any clarification

[PatrickF]

Hello,

I'm not specialist of STPMIC1, but reading the datasheet make it clear there is no 'bypass' bit for Boost converter. The bypass mode is automatic above 5.2V (as there is no need to boost the VIN to cope with USB voltage requirements). I'm not sure inductor could be omitted in you always ensure VIN>5.2V. I will check if I can get an answer.

[PGE]

Thanks for the clarification so in any case we need the BOOST powered. Nice if you can check for the inductor.

[Vincenzo]

Hello,

unfortunately you cannot bypass the inductor, it is dangerous you can destroy internal driver of the boost converter, you must remove the inductor component and use the SW switch instead of the USB_SW. you can connect SWIN to the 5Vin and you are able to turn ON/OFF SW switch so you can have the 5V to the SWOUT pin

Regards

[PatrickF]

@PGE​, please click on 'Select as Best' if last reply solved your issue or answered your question.

[PGE]

Thanks for clarifcation. If the BOOST and PWR_USB_SW  are not used at all. How do we have to connect BOOST input ?

[PatrickF]

You could leave BOOST pin open. As example, see STM32MP157C-DK2 board schematics.