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sburr
sburr
Associate II
November 16, 2015
Question

STM32F and USB at 1.8V

  • November 16, 2015
  • 3 replies
  • 1134 views
Posted on November 16, 2015 at 18:54

I would like to connect an STM32F405 to usb while running the chip at 1.8V. Since USB requires 3.3V I need some kind of level translator. I have tried the TSX0102 and did not get it working. Has anyone done this before or could recommend a level shifter chip for USB?

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    3 replies

    Tesla DeLorean
    Tesla DeLorean
    Guru
    November 16, 2015
    Posted on November 16, 2015 at 19:04

    Are you sure this is a remotely practical approach?

    Have you considered the

    http://www.st.com/web/catalog/mmc/FM141/SC1169/SS1580/LN1840/PF260095?icmp=pf260095_pron_pr_feb2015&sc=stm32l476-pr

    , the L4 has a specific VDDUSB pin to deal with this issue.

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    sburr
    sburrAuthor
    Associate II
    November 17, 2015
    Posted on November 17, 2015 at 17:27

    We don't want to switch processors for many reasons, I would like to run an STM32F405 on 1.8V and still have USB capability. There is nothing in the 405 datasheet about how the usb phy works, is it just push pull?

    Tesla DeLorean
    Tesla DeLorean
    Guru
    November 17, 2015
    Posted on November 17, 2015 at 19:29

    The pins have specific drivers for the USB bidirectional/differential requirements that meet the USB specs. I think the advice in the past is to increase your supply voltage when you expect to be using USB. I don't think ST has made representations that the USB PHY will meet specs at lower voltages.

    Perhaps the External PHY mode offers some additional flexibility, but I'm hard pressed to see that some external auto-direction converters are going to get the job done on the regular pins.

    What's available is likely highly specialized, and expects more control signals than you can deliver.

    http://www.ti.com/lit/ds/symlink/sn74avc2t872.pdf

    Your best bet is to talk with your ST FAE about this.

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