STM32F746NG USB Host (HS) embedded PHY and VBUS.

[Peter Morrow]

Posted on May 02, 2018 at 18:00

Hi,

I'm looking at trying to implement a USB host (MSC) driver using the high speed core on the STM32F746NG MCU, we do not have an external PHY so are using the embedded PHY.  How does one achieve the 5v required for VBUS to the attached device (USB stick) in this situation?  It looks like the FS core has an internal charge pump which can be used to step the 3v3 IO up to 5v, but I can't see anything like this for HS with the embedded PHY.

Thanks,

Peter.  

[waclawek.jan]

Posted on May 03, 2018 at 00:47

It looks like the FS core has an internal charge pump which can be used to step the 3v3 IO up to 5v,

No. Where did you see that?

The OTG chapter in RM0385 is common for bot OTG_HS and OTG_FS and is very specific in this; the following quote appears verbatim *twice*:

On-chip 5 V V BUS generation is not supported. For this reason, a charge pump or, if 5 V are

available on the application board, a basic power switch must be added externally to drivethe 5 V V BUS line.

Btw. I find it a silly idea to supply VBUS to USB device using a *charge pump*. A boost converter would be a more appropriate expression IMO, if the primary power source is below 5V.

JW

[Peter Morrow]

Posted on May 03, 2018 at 10:05

Hi,

My post is a fine example of not thinking before posting, I saw there was a STMPS2141STR power switch on the stm32f746ng-disco board which is used with the FS core.  We in fact have one on our board too (in fact we have 2, 1 for HS (no phy) and the other for FS).

Please disregard the question.  I'd delete the post if it were possible.

Peter.