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jacky
jacky
Associate II
July 8, 2018
Question

STM32F0 Discovery Board 5V Output Current Limit

  • July 8, 2018
  • 6 replies
  • 2087 views
Posted on July 08, 2018 at 10:31

Hi all,

I have a STM32F0 Discovery board and would like to use its 5V power pin (pin 1) to power external devices (LEDs).  The user manual UM1525 section 4.3 says that the power consumption must be lower than 100mA.  However, when I look at the schematics on pg38, the 5V pin is connected to the USB Vcc through a BAT60JFILM diode, which is a 1A part.  Anyone know why the power consumption is limited to 100mA?

Thanks.

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    6 replies

    Tesla DeLorean
    Tesla DeLorean
    Guru
    July 8, 2018
    Posted on July 08, 2018 at 15:12

    The diode doesn't supply 1A, it is a maximal draw rating, the amount that can flow through the component, the current has to flow from some where else.

    For USB applications there is a maximum total budget of 500mA once the system has negotiated connectivity, but initially the limit at startup is 100mA

    http://www.ti.com/lit/an/slyt118/slyt118.pdf

     
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    jacky
    jackyAuthor
    Associate II
    July 9, 2018
    Posted on July 09, 2018 at 00:33

    Thanks for your reply.  So the limit is due to the USB port instead of the evaluation kit itself?  If the USB port is able to supply 500mA or 1A without enumeration, is it OK to use the 5V pin to supply current > 100mA?

    I am thinking about the situation when the board is powered by a USB battery pack.  

    Thanks.

    T J
    T J
    Senior III
    July 9, 2018
    Posted on July 09, 2018 at 01:47

    The inference being that you have to charge the battery pack ?

    thereby requiring  a higher current ?

    is that what you are asking ?

    USB always had the 100mA limit, as a fault detector.

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