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PCM2707C: D+ pullup

Part Number: PCM2707C

Hi

My customer have the issue of leak current to Host through the USB D+.

Is It any problem the following circuit that is used external power supply for D+ pull-up instead of VDD?

3.3V is made by DCDC from Vbus input.

Should we use VDD pullup at Bus powered mode?

Muk

  • Hi Mukuno-san,

    I believe the issue is caused by delay in the DCDC generating the 3.3V when the USB is connected.  The PCM is likely being powered before the DCDC output is at the desired 3.3V.  Connecting the pull-up to the VDD pin of the PCM should solve this issue.

    Thanks,

    Paul

  • Hi Paul-san,

    Sorry for your confusing.

    Now, customer is using pullup power source from VDD. The issue was occurred at this condition.

    So, they are considering to change pullup power source from VDD to external 3.3V.

    Their question, is it no problem?

    Muk

  • Hi Paul-san

    (Additional question)

    The recommended operating conditions of VBUS in the Datasheet is from 4.35V to 5.25V

    However, I think, In case of Self-powered mode, Vbus can accept 3.3V power supply. Is it correct? (Vbus in the Figure 37 is connected 3.3V. )

    If yes, could you please let me know the range(min , max) of Vbus at self-powered mode?

    Muk

  • Hi Mukuno-san,

    When the device is in self-powered mode, VBUS should be connected to VDD.  In this mode, the VBUS pin has the same limits as the VDD pin.  Please refer to the image below:

    In regards to the DCDC driving the pull-up resistor - that is okay as well, as long as the output of the DCDC is off when the USB is disconnected.

    Thanks,

    Paul