Current Consumption

[hilwan]

Posted on April 02, 2014 at 10:49

Hi all,

I'm using the F3 Discovery. I want to use an external board by powering it using the external application power supply 5V of my Discovery. I measured my the current consumption of my discovery alone and it's about 40 mA. How can i determine the maximum current that my Discovery can offer to this external board? Thanks in advance

[chen]

Posted on April 02, 2014 at 11:23

Hi

Please tell us which F3 discovery board you have (there may be more than 1). ''How can i determine the maximum current that my Discovery can offer to this external board? '' Technically, the 5V pin on the discovery boards are inputs - it is to supply 5V to the discovery board. It is used to supply the 3V3 LDO regulator on the board which then supplies the STM32 with 3V3. How are you powering your board at the moment ? USB, external PSU or battery

[hilwan]

Posted on April 02, 2014 at 11:59

I have STM32F303VC.

I read that this pin could an input/output. My F3 Discovery is powered by USB ST-link and i want to add an external charge to this board so i need (5V,50mA)

[chen]

Posted on April 02, 2014 at 12:07

Hi

''I read that this pin could an input/output.'' It can be an output if 5V is being supplied to the board. ''My F3 Discovery is powered by USB ST-link'' The USB is supplying the 5V in your case. ''i want to add an external charge to this board so i need (5V,50mA) '' Technically, each USB device is allowd upto 500mA - I think so your 50mA should be OK, it depends how much current the ST-Link takes itself (Do bear in mind the USB cable length - anything longer than 1m may cause voltage drop as the current load increases. 50mA should not cause you a big problem)

[hilwan]

Posted on April 02, 2014 at 13:55

Ok, thanks for your response.

 ''Technically, each USB device is allowd upto 500mA - I think so your 50mA should be OK, it depends how much current the ST-Link takes itself'' : I don't know why when i powered with 5V an another F3 Discovery to the one powered by the USB, the embedded St-link of the both board were burnt. So i can't reprogram them anymore. But when i powered them by the USB user for example, it's ok. I don't know how to fix this issue, is there any trick to resolve it ?  

[chen]

Posted on April 02, 2014 at 15:07

Hi

'' I don't know why when i powered with 5V an another F3 Discovery to the one powered by the USB, the embedded St-link of the both board were burnt. So i can't reprogram them anymore. '' It sounds like the STM32 used for the ST Link has been destroyed. Possibly because it had been wired up badly?!? (Though the ST-Link on the eval boards can be used as stand alone, they do not have the protection chips that the seperate ones have http://uk.farnell.com/stmicroelectronics/st-link-v2/icd-programmer-for-stm8-stm32/dp/1892523 ) ''I don't know how to fix this issue, is there any trick to resolve it ?'' From what you have described, the on board ST Link is destroyed. You can use one from the link I have posted. Use the jumper link on the dev board to connect the external version. Check the circuit diagram for details of the correct connection. Actually, sounds like power the STM eval boards through the ST-Link is a bad idea for your purpose.

[hilwan]

Posted on April 02, 2014 at 15:34

Ok, thank very much sung.chen_chung

Best regards

[frankmeyer9]

Posted on April 02, 2014 at 16:24

It sounds like the STM32 used for the ST Link has been destroyed.

Possibly because it had been wired up badly?!? One should really think twice before attaching two different means of power supply to one board. That is especially true if both sources are powered by mains. Huge transient currents may flow, destroying the board. I can't even connect one STM32F3-Discoverboard to the RS232 connector when STLink-USB is plugged in (on the same PC!). If I do so, the debugger freaks out, and loses connection.

[hilwan]

Posted on April 03, 2014 at 11:20

''I can't even connect one STM32F3-Discoverboard to the RS232 connector when STLink-USB is plugged in (on the same PC!). If I do so, the debugger freaks out, and loses connection'' : It's good to know that. Thanks