STM32F091 Power and Speed

[d_aliaga]

Posted on February 25, 2016 at 10:28

Hello everybody and thanks for your help.

I have been reading a document called: UM1724 STM32 Nucleo 64 boards User Manual and although very useful (more than other documents) it still left me a little confused so I ask for your helpFirst Power. I have been using my nucleo so far connected to the computer through USB. The USB also powers the nucleo. Now I want to power up the nucleo by itself. Apparently there are three options: VIN, E5V (

which is different than +5V pin)

 and +3V3 (which I dont know if it is different or not from +3.3V pin) I was going to ask which to use but I read that if I use the +3V3 option, I wont be able to reprogram my nucleo so I am discarding it. There are two options left: VIN and E5VHowever the manual says that VIN requires from 7V to 12V, BUT I have a pin layout of the STM32F091 that next to the VIN pins says ''5v-9V''... So which is it???So, which should I use? Or in other terms, what are the pros and cons for choosing one pin over the other? I am planning also to use the +5V pin (which is different than the E5V- one is output the other input) to power up the rest of circuitry I plan to use. Any comment?2) Now the second thing. which I am even more confused. The nucleo announces itself as 48MHz. However I read in the manual that maybe it is using ''MCO from ST-link''?? in which the speed is 8MHz?? (No wonder it seems slow!) The SBs and Rs are just as default (from the box) so which is the timing option I am using??? Apparently since SB55is OFF SB16 and SB50 is ON  and I dont see any R35 R37 there, this is the option....How can I get the announced 48MHz??? Should I use the X2 crystal that appears to be there?? Or is another X3 required?? or an external oscilator through pin 29 of the CN7?Thank you very much for your help and advice

[Tesla DeLorean]

Posted on February 25, 2016 at 12:25

The input clock is 8MHz but this is multiplied up with an VCO/PLL arrangement configured in system_stm32fxxx.c

The linear regulator has a dropout voltage, so you'll want to take that into account for it to get to 5V from your input. The regulator is likely rated for 12V operation but will generate a lot of heat and have a reduced current rating. The sweet spot would be 7V. With other shields you'd need to determine their requirements.