Hi,
I´m trying to get a STM32H747 Discovery board together with USB Host to operate at 1.8V VDD.
At 3.3V VDD_MCU USB is working fine!
What I´ve done:
1. Removed jumper on JP3 and supplied VDD_MCU with 1.8V.
2. Removed SB10 and supplied VDD33USB with 3.3V.
3. Removed R33 and supplied USB_VDDIO (pin 32 on USB3320) with 1.8V.
4. Verified that R136 is not mounted and R137 is mounted.
What is working:
A. The MCU is working fine at 1.8V. I´m running at 400MHz at voltage scale 1 (using the SMPS).
B. VBUS is started (USB3320 controls U2) and LD7 lights up.
C. When a usb device is inserted, its looks like its recognized. The usb stack connects a device, initiates a reset and then I get Control Errors.
A had a look around the forum and found this post:
https://community.st.com/t5/stm32-mcus/how-to-check-compatibility-on-usb-ulpi-transceivers-with-stm32/ta-p/657275
However, the REFCLK for the USB3320 is 24MHz, so not sure that post above is what I´m seeing.
The reason I need 1.8V IO operation is that I´m using a Wifi module (connected via SDIO interface) that only support 1.8V IO.
My best guesses/questions:
1. Some timing is violated.
2. X1 is supplied with 3.3V so REFCLK for is at 3.3V IO. But according to datasheet (USB3320), Voh for REFCLK is between 0.68 *VDD18 and VDD33 (internally generated by USB3320). So this should not be an issue.
3. It is not clear what IO level the ULPI interface of the STM32H7 is referenced to when assigning a pin to an alternate function (OTG_HS_ULPI_X). VDD or VDD33USB.
4. Something that I completely missed...
