1.8V VDD and 3.3V VUSB

[amel]

Hi,

I’m using an STM32L052 with LQFP32 package, VDD = 1,8V.

According to the datasheet:

“VDD_USB = 1.65 to 3.6V: external power supply for USB transceiver, USB_DM (PA11)
and USB_DP (PA12). To guarantee a correct voltage level for USB communication
VDD_USB must be above 3.0V. If USB is not used this pin must be tied to VDD or VSS.
On packages without VDD_USB pin, VDD_USB voltage is internally connected to VDD
voltage”

Since in the LQFP32 package VDD_USB is internally connected to VDD, it is therefore powered at 1,8V in my design.

As expected, the USB interface does not operate when I connect the board to a PC and risk of damage because D+ and D- tied to 1,8V

Could you please confirm that the internal USB PHY cannot operate correctly at 1,8 V, and that USB operation requires VDD ≥ 3.0 V even when VDD_USB is internally tied to VDD ?

If so, what would be the recommended workaround for designs that operate the MCU at 1,8 V ?

Thanks in advance for your clarification.

[FBL · Accepted solution]

Hi @amel 

Sorry for hearing that! Indeed, USB PHY cannot operate at 1.8V. I'm escalating this to dedicated team. It is mentioned in page 18, to be USB compliant from the I/O voltage standpoint, the minimum VDD_USB is 3.0 V. also in hardware getting started app note.

The only workaround I see to use different package STM32L052 C6/R6/C8/R8. I mean LQFP48 would be less expensive.

[amel]

Hi,

Thank you for your reply.

So I have two Options :

1- Change the package to one who VDD_USB is pin accessible

2- Change system voltage (VDD)  to 3,3V (3,0V Minimum)

okey, need recalculations

Best regards,

[FBL]

Yess @amel 

Internal ticket is submitted to dedicated team 221635 to clarify the datasheet.