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TUSB1002A: Optional pulldown resistor for RX port with HD3SS3320

TerryU
Prodigy 145 points
Part Number: TUSB1002A

Hi Experts,

TUSB1002A document mentions an optional pulldown resistor, 220kohm, for RX port for discharging . I would use TUSB1002A with HD3SS3320, Type-C MUX, for Type-C configuration. In this case, should I consider about this pulldown resistor? And if so, which is put the pulldown pre-MUX or post-MUX?

Best regards,

Tetsu 

  • 0
    TI__Guru**** 152576 points

    Tetsu-san

    The 220k resistors help to further reduce the discharge time to be well within the spec limit of 250 ms. As stated in the TUSB1002A these resistors are not required assuming leakage current from external components is enough to discharge capacitor. There will only be signal integrity impact to USB performance if the resistors are added. The stub created from placing the optional (not necessary) pull down resistor should be minimized to avoid negative affects. 

    Thanks

    David

  • 0 in reply to David (ASIC) Liu
    Prodigy 145 points

    Hi David,

    Thank you for your rapid response. This optinal  resistor works quick discahrage of coupling capasitors, and TUSB1002A RX port does not have discharge system. What will occur, if charge remains a bit large term?

    Best regards,

    Tetsu

  • +1 in reply to TerryU
    TI__Guru**** 152576 points

    Tetsu-san

    The Tdischarge spec is there to ensure that the USB receiver, at the connector, does not hold a previous common mode voltage and prevent a newly plugged device form seeing this common mode.

    Thanks

    David

  • 0 in reply to David (ASIC) Liu
    Prodigy 145 points

    Hi David,

    Thank you for your useful comment. I will consider about discharge.

    Thanks,

    Tetsuj