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matt-crc
Graduate II
October 27, 2025
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STM32N657-DK board bug or Documentation error?

  • October 27, 2025
  • 1 reply
  • 212 views

In the default configuration, the SMPS on the development board is disabled.  As such the VDDA18PMU appears to be floating.  According to the spec sheet, it says that the pin MUST be tied to Vss when the SMPS in not used.  Is there an internal pull down?

    This topic has been closed for replies.
    Best answer by ELABI.1

    Hi @matt-crc,

    There is no internal pull-down resistor on this pin.

    Note: The connection schematic of VDDA18PMU and VDDSMPS on this board does not exactly match the recommendations in AN5967 (Figure 4: System supply configurations) because the STM32N657-DK board was designed much earlier than the application note.

    You can refer to application note AN5967 section 3.7 System startup and the Datasheet DS14791, specifically section 3.4.4 SMPS usage, which provide guidelines to follow for using the SMPS.

    When the design is in SMPS Bypass mode (SMPS disabled), VDDA18PMU, VDDSMPS, and VFBSMPS must be connected to ground (GND) to prevent them from floating.

    Thanks.

    ELABI.1

    1 reply

    E
    ELABI.1Answer
    Technical Moderator
    October 28, 2025

    Hi @matt-crc,

    There is no internal pull-down resistor on this pin.

    Note: The connection schematic of VDDA18PMU and VDDSMPS on this board does not exactly match the recommendations in AN5967 (Figure 4: System supply configurations) because the STM32N657-DK board was designed much earlier than the application note.

    You can refer to application note AN5967 section 3.7 System startup and the Datasheet DS14791, specifically section 3.4.4 SMPS usage, which provide guidelines to follow for using the SMPS.

    When the design is in SMPS Bypass mode (SMPS disabled), VDDA18PMU, VDDSMPS, and VFBSMPS must be connected to ground (GND) to prevent them from floating.

    Thanks.

    ELABI.1

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