How do I connect the STM32F4 Discovery to external power?

[sandtime]

Posted on October 22, 2014 at 07:20

For the STM32F4 Discovery board, can someone tell me exactly what pins need to be connected in order to power this externally (i.e. not via USB)?

Surprisinginly, I can't find any place where this information is clearly stated.  

I'm assuming that I need to connect 5V and ground.  But do I need to supply 5V on both 5V pins, or just one of them?  Do I need to only connect one Ground pin, or do I need to tie them all together externally?  Do I need to do anything with Vdd?  Etc...

Any help would be appreciated.  Thanks!

[chen]

Posted on October 22, 2014 at 10:46

Hi

'' can someone tell me exactly what pins need to be connected in order to power this externally (i.e. not via USB)?''

Connector P2

Pin 1 & 2 are 0V

Pin 3 & 4 are 5V in

Pin 5 & 6 are 3V in

If you use these - it is your responsibility to

1) get the polarity right

2) Maintain the correct voltages

3) provide enough current capability

''Surprisinginly, I can't find any place where this information is clearly stated. ''

http://www.st.com/web/catalog/tools/FM116/SC959/SS1532/PF252419

Look at UM1472 or the schematics for the board

''I'm assuming that I need to connect 5V and ground.''

Yes. (or just 3V and 0V)

''But do I need to supply 5V on both 5V pins, or just one of them?''

No, they are joined together but using both is better.

''Do I need to only connect one Ground pin, or do I need to tie them all together externally?

You can get away with only connecting one 0V point BUT it depends......

electronics is complicated.

If you are using any of the analogue functions (ADC or DAC) - you may want to consider

seperate power supply to the analogue parts of the device (though the header may not provide access - I have not looked)

Connecting them all together can be better (or can cause 'ground loops' - I said electronics is complicated! )

'' Do I need to do anything with Vdd? ''

If you use the 5V pin, then you do not need to use the Vdd pin on P1 (I think)

[sandtime]

Posted on October 22, 2014 at 20:04

Thank you!

I did look at UM1472, but I still didn't see anywhere that clearly stated how to connect the board when powering it externally.

As a quick clarification, if I supply 5V in, do pins 5-6 become 3V out?  If not, how can I get 3V out while putting 5V in?  

The user manual is unclear about the conditions which allow 3V output on those pins - it only says that this happens when another application board is connected.

[chen]

Posted on October 23, 2014 at 10:39

''I did look at UM1472, but I still didn't see anywhere that clearly stated how to connect the board when powering it externally.''

It is all in there. You have to look at the schematic (or circuit diagram) and the pictures/diagrams of the board.

''As a quick clarification, if I supply 5V in, do pins 5-6 become 3V out?  If not, how can I get 3V out while putting 5V in?  ''

Yes, 5 & 6 will have 3V on them. Be careful how much current you draw from the 3V, it will depend on a) how much current your 5V can supply and what current the 3V LDO is capable of.

''The user manual is unclear about the conditions which allow 3V output on those pins''

Sadly, you have to look at and understand the schematic. The schematic shows a 3V LDO

(LD3895).

So long as you supply 5V to the board either through the USB or the P1 5V pins then 3V will be available.

The LDO is also protected with a diode, so you can actually supply the board with 3V (but them 5V will not be available and It looks like the 2.5V will not be available - not sure what 2.5V is used for on the board)