UST OTG configuration

[Ricko]

Hi,

I am thinking using the STM32U5G9VJT6Q and configure the USB to USB-OTG but never used USB OTG before.

The PCB would have its own power supply and only work when power is applied through it and never take power from the USB connector. The USB would also be USB 2.0 using Type C connector but without any of the fancy external ICs for handshaking and power management.

Considering the above and configuring the USB to OTG (so I can change it to be either device or host at runtime):

- if configured as host, I assume the power to the device connected be provided directly from the 5V of the PCB without any microcontroller control of it. Is that correct?

- for the OTG is the OTG_HS_ID pin I assume I connect it straight to the MicroUSB connector or Type-C connector. Is that correct or do I need to have some logic/devices in between?

Thank you :)

[FBL · Accepted solution]

Hi @Ricko 

1. In host mode, you may be able to provide 5V directly from the PCB to the VBUS pin of the USB connector, as long as the 5V supply is stable and can provide sufficient current for the connected device. However, you won't have the ability to control power through the microcontroller, which is required for proper USB compliance.
2. Using Type-C connector, you don't need ID pin. U5Gx embeds UCPD peripheral, so you can handle power role swap using CC lines with TCPP03 protection for example. You can refer to MB1550 as a reference.
3. Using Micro-USB connector, you will need OTG functionality. as stated in section 72.5.1 ID line detection in RM0456, you can apply SRP protocol. This protocol allows A device, which may be battery powered, to conserve power by turning Vbus off when there is no bus activity while still providing a means for B device to initiate bus activity. A device is allowed to respond to SRP and B device is allowed to initiate SRP. AFAIK, OTG Host must be able to source minimum of 8mA