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STM32F40x DFU Requirements

Question asked by Mr. Blinky on Jan 20, 2015
Latest reply on Jan 20, 2015 by Mr. Blinky
I've made my first PCB with the STM32F405RGT6 but unfortunately the DFU isn't working.  The device is never detected despite booting with the appropriate BOOT0/BOOT1 and FS_DP, FS_DM, and FS_ID connected.  I'm trying to troubleshoot and I have a few questions.

1. Anecdotal posts I've found along with docs for other STM32 parts seem to suggest that OTG_FS_VBUS needs to be >4V during selection (in addition to DP, DM, and ID) for DFU to work.  However, page 48 of AN2606 doesn't list OTG_FS_VBUS as a requirement for the STM32F40x.  A lot of designs I've reviewed have OTG_FS_VBUS (PA9) connected though suggesting it may be required.  Some examples of related chatter on this are:!topic/phoenixpilot/B2q-Cwxx9fs

2. Page 17 of AN2606  (general section) depicts DP being pulled high using OTG_FS_VBUS.  I can't find what they're talking about in the note below to determine if I need this.  FWIW, all designs I've reviewed for STM32F40x parts don't implement this pull-up so I didn't either.

3. The DM/DP/ID traces are 10/10mil and only about 150mil long and the length of DP/DM are within 5mil of each other.  I haven't calculated controlled impedance but I figured I would be fine sticking with only USB FS (not HS).  Is it possible the problem could be here or does this sound fine?  I'm hoping I don't have to dig in too deep in this area since it's outside my current PCB skills.

4. ...any other troubleshooting steps I should take?