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[TPS65920] External PD resistor on VBUS

Antony Lin
Genius 13480 points
Other Parts Discussed in Thread: TPS65920

There's a special situation we need to add external 75kohm resistor on VBUS as below.

The only USB function required for this OMAP platform is to act as a USB-Device (connected to PC for data transfer.)   In addition, we need to detect a non-USB accessory plug-in event by detecting VBUS voltage.  (The pin is connected to a big PU resistor to 5V on the accessory board.)  Therefore, we need to add a 75kohm PD resisotr @ VBUS pin on this OMAP platform.

The question would be, is there any side effect to add 75kohm considering only USB-Device mode is required?

Antony

  • 0
    TI__Genius 15100 points

    Hi,

    What do you mean by non USB accessory plug event?

    If you have a pull down then the VBUS resistor will be affected. Do you want a PU and a PD, not really sure about your use case.

     

    Regards,

    Gandhar.

  • 0 in reply to Gandhar Dighe
    TI__Genius 13480 points

    Hi Gandhar,

    You can consider there's an accessory with several pins.  When the accessory is connected to the OMAP platform, one of the pin (pull up to 5.3V through 1M ohm on accessory) will be connected to TPS65920's VBUS pin.  But, the functionality of this accessory is irrelevant to USB. 

    Their purpose is to have a voltage<0.2V on this pin when the accessory is connected to OMAP platform.  Therefore, they need to add a PD resistot on TPS65920-VBUS pin.  (Now they consider to change this PD resisor value to 20k ohm.)

    Meanwhile, the TPS65920 USB PHY need to be a USB-client when connected to the PC (USB host) for USB data transfer.  We need your help to confirm if there'll be any side effect when connecting to a USB host considering there's a 20k ohm PD resistor on VBUS pin.

    Thanks,

    Antony