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DBhut.1
DBhut.1
Senior
October 11, 2022
Solved

STM32L412CBT6 VDDUSB Pin status for ultra low power Application

Hello,

I have used STM32L412CBT6 microcontroller in my recent Project.

I have query regarding "VDDUSB" pin that I am not using it in my ultra low power application.

So, Can I keep that Pin Floating or any Component Connection would be needed?

Thank You

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    Peter BENSCH
    Peter BENSCHBest answer
    ST Technical Moderator
    October 11, 2022

    The data sheet of the STM32L412 says:

    • Table 18, 19: “All main power (VDD, VDDA, VDDUSB, VBAT) and ground (VSS, VSSA) pins must always be connected to the external power supplies, in the permitted range.�?
    • Table 21: “VDDUSB: USB supply voltage, USB not used = 0…3.6V�?
    • 3.9.1 Power supply schemes:
      • […] When the functions supplied by VDDA or VDDUSB are not used, these supplies should preferably be shorted to VDD.
      • If these supplies are tied to ground, the I/Os supplied by these power supplies are not 5 V tolerant.

    Allowing something to float is usually a gateway for interference. You can certainly connect VDDUSB to GND, but then the 5V tolerance of the GPIO is missing. That is why it is also recommended to put VDDUSB on VDD when USB is not used.

    For ultra low power applications, connecting to GND might be the best option.

    Regards

    /Peter

    In order to give better visibility on the answered topics, please click on Accept as Solution on the reply which solved your issue or answered your question.
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    3 replies

    Peter BENSCH
    Peter BENSCHBest answer
    ST Technical Moderator
    October 11, 2022

    The data sheet of the STM32L412 says:

    • Table 18, 19: “All main power (VDD, VDDA, VDDUSB, VBAT) and ground (VSS, VSSA) pins must always be connected to the external power supplies, in the permitted range.�?
    • Table 21: “VDDUSB: USB supply voltage, USB not used = 0…3.6V�?
    • 3.9.1 Power supply schemes:
      • […] When the functions supplied by VDDA or VDDUSB are not used, these supplies should preferably be shorted to VDD.
      • If these supplies are tied to ground, the I/Os supplied by these power supplies are not 5 V tolerant.

    Allowing something to float is usually a gateway for interference. You can certainly connect VDDUSB to GND, but then the 5V tolerance of the GPIO is missing. That is why it is also recommended to put VDDUSB on VDD when USB is not used.

    For ultra low power applications, connecting to GND might be the best option.

    Regards

    /Peter

    In order to give better visibility on the answered topics, please click on Accept as Solution on the reply which solved your issue or answered your question.
    DBhut.1
    DBhut.1Author
    Senior
    October 13, 2022

    thank you so much for this brief answer.

    Peter BENSCH
    Peter BENSCH
    ST Technical Moderator
    October 13, 2022

    Very nice! I hope it helps you a little with your application.

    Regards

    /Peter

    In order to give better visibility on the answered topics, please click on Accept as Solution on the reply which solved your issue or answered your question.
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