STM32F4 Discovery USB OTG Power Switch

Rogers.Gary · ‎2015-01-25

Posted on January 26, 2015 at 03:47

On the Discovery user Guide:

DM00039084_STM32F4_Discovery_User_Guide

On Page 39, there is a power switch: STMPS2141STR that has +5V connected to the input side. The data sheet for this does not indicate and voltage drop through - as there should not be if it is low on resistance switch. However, the output connects to teh USB port, and also finds it's way to pin PA9 (of the STM32F4.

Is it OK to drive 5V to the STM32F4 PA9 pin if it's supply is a regulated 3.3V?

(my first time working with USB, sorry for this question if it's something obvious)

Thank you...

Tesla DeLorean · ‎2015-01-25

Posted on January 26, 2015 at 05:03

I think you'll find PA9 is designated FT (Five volt Tolerant) per the Data Sheet.

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Rogers.Gary · ‎2015-01-26

Posted on January 26, 2015 at 21:25

Thank you for pointing that out. I did look through but could not (did not) see where that was stated, so I'll check it again. Probably electrical specs...

The bigger question is - if my design (Host) is 3.3V, and USB is compliant at 3.3V, why would I want to use 5V to the USB ? It would cost another regulator. What am I missing? Or, why did ST take the 5V option on the Discovery board?

Thanks again...