STM32F4-Discovery: R30 (Boot0) Value. What is acceptable?

[shawn2]

Posted on November 19, 2015 at 20:09

I'm developing a low power solution using only the devboard, however I'd like to be able to buy some mA by increasing the value of R30.  Would changing this to say a 10k SMT effect anything?  Alternatively, the only way for me to buy the power would be to come off VDD entirely (desoldering that) and only using VBAT?  Will the system function the same under VBAT only?

Right now I'm feeding 3V straight to VDD.

[Tesla DeLorean]

Posted on November 19, 2015 at 22:23

I suspect you could get away with a singular 100K pull-down on the pin.

Not sure about your VBAT comment, the supply needs to enter via VDD, and VDDA, the latter has the power-on-reset circuitry attached, there's no path from VBAT to the primary supply for the processor, just the RTC/BKP/PWR stuff. Have you considered and

http://www.st.com/web/catalog/tools/FM116/SC959/SS1532/LN1848/PF261635?sc=stm32l4-discovery

board, designed for battery powering

[shawn2]

Posted on November 19, 2015 at 23:45

So desolder the bridge and come off the Boot0 pin with a 100k pulldown?  That sounds good to me.  Easier than mounting an SMT.

I've also already got an L4-Disco and have recommended it.  Nifty board.  It wont make this iteration, however, so I need to get by with the F4 for now.  I've gotten it down to 1.4mA with a dedicated 3V regulator attached, boot1 desoldered,  powered direct to VDD, and everything else put to sleep.

[shawn2]

Posted on November 25, 2015 at 02:03

Update:  I couldn't get it to boot with anything above 5K on that pin.  So 100K is a no-go.  Oddly, the power draw was only a 100uA difference between the 470ohm and the 5Kohm.  Not sure how that could happen.

In standby, VDD should be sunk mostly to GND through that resistor.  Should be drawing 6mA+.