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June 3, 2011
Question

STM32F107RC - Very low external resistor on NRST pin

  • June 3, 2011
  • 5 replies
  • 1348 views
Posted on June 03, 2011 at 23:59

Hi,

I want to build circuit with STM32F107RC. I projected PCB and chcek all wires with any avaluation kit board. When I turn power on all circuit take about 9 mA. I chcecked all power supply pins aroud microcontroller and I egazmined all voltages.

All voltages was 3,331V. I egzamined BOOT0 and BOOT1 switches. All is OK. BOOT0 is logical 1, BOOT1 is logical 0. On NRST pin I have 0,441V with pull-up resistor 10k. When I exchange on NRST pin resistor to 100 ohm on pin I have 3,110V and microcontroller runs. General current is about 50mA and all look very good.

In this case I can use JTAG for upload firmware and I can use RS-232 for upload firmware.

Why my STM32F107RC requires more low resistance on pull-up NRST pin ? I have 2 this components and all 2 components work similary. Would you like tell me what I do bad ? I read more materials in net, but anybody don't written about this problem in the past.

Best regards,

Mario
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    5 replies

    Tesla DeLorean
    Tesla DeLorean
    Guru
    June 3, 2011
    Posted on June 04, 2011 at 01:30

    You don't have the part wired properly, either you have something external on NRST, or the voltages on VDD,VDDA are wrong and the power supply supervisor is trying to hold the device in reset.

    50 mA seems kind of high.

    You don't provide a schematic so we're left to guess.
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    programmer
    programmerAuthor
    Associate
    June 4, 2011
    Posted on June 04, 2011 at 09:55

    Hi,

    I attached schematic also in PDF format. It is very, very simple solution because I will use thismicrocontroller for FFT transformation for measurement. In this aplication I had low dinisity microcontrollerSTM32F101 in the past andall was right.

    Regards,

    Mario

    ________________

    Attachments :

    VMF-4_sch1.pdf : https://st--c.eu10.content.force.com/sfc/dist/version/download/?oid=00Db0000000YtG6&ids=0680X000006I0rM&d=%2Fa%2F0X0000000beb%2FotxO4Nm9CKZwpfauk.bwW.FFJ3NL9oahucErX5sDlZ0&asPdf=false
    Tesla DeLorean
    Tesla DeLorean
    Guru
    June 4, 2011
    Posted on June 04, 2011 at 13:43

    I'd check the part placed for C20.

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    programmer
    programmerAuthor
    Associate
    June 4, 2011
    Posted on June 04, 2011 at 23:12

    Hi,

    I checked cacasitor C20 and in this place really was mistake. I unmounted this part and I chceck it in measurment bridge. This part worked as rasistor 1k1 and all is clear now. All situations and all measurments are clear when in this place was mount enement with resistantion character only.

    Many thanks, and to next time.

    Best regards,

    Mario

    peterm
    peterm
    Associate II
    September 29, 2012
    Posted on September 29, 2012 at 14:33

    I had a similar problem with nRST being low. Clive1's suggestion to check Vdda was spot on - my filter resistor was too big and this was only 1.8V. Once I dropped the resistor so the voltage was higher the problem went away.

    Thanks Clive1!

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