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USB D+/D- voltage versus STM32F103 VDD voltage

Question asked by Bertrand3159 on Apr 18, 2014
Hi,

You probably already get such discussion.
I am currently designing a board based on STM32F103RC6 MCU that I want to supply with Vbat=3V6, VDD1/VDD2/VDD3/VDD4=VDDA= 2V4 but in the data sheet, the Vdd min in the USB DC electrical characteristic table is given at 3V0. 

I looked on the different evaluation board schematic, all of them configure the STM32F103 VDD supply at 3V3 which is not helpful.

Knowing that I have to control the 1K5 pull up resistor to USB D+ with the STM32, could you help me on the USB schematic for my supply configuration?
Should  I set:
-  VDD1/VDD2/VVD3/VDD4=2V4 and USB D+ pull up to 2V4
  or 
-  VDD1/VDD2/VVD3/VDD4=2V4 and USB D+ pull up to 3V3.

Thanks in advance for your help
Regards
Bertrand

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