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HD3SS3220: What is the significance of using 900K resistor for "VBUS_DET" Pin?

Purvi Gupta
Prodigy 30 points
Part Number: HD3SS3220

Tool/software:

Hi Team,

What is the significance of using 900K resistor for "VBUS_DET" Pin? How does external 900K and internal 95K resistor satisfies the threshold condition of 3.3V (Typ) ? Can you share the internal circuit of "VBUS_DET" Pin?

And can we use 10K external resistor instead of 900k when VBUS voltage is 5V?

Regards,

Purvi

  • 0
    TI__Mastermind 21775 points

    Hi Purvi,

    Purvi Gupta said:
    What is the significance of using 900K resistor for "VBUS_DET" Pin? How does external 900K and internal 95K resistor satisfies the threshold condition of 3.3V (Typ) ? Can you share the internal circuit of "VBUS_DET" Pin?

    The 900KOhm resistor is required in order to ensure that the system VBUS can be detected without causing damage to the device. You should not use any value aside from what is listed in the datasheet. I don't believe we can share the internal circuit, but I can double check on that.

    Purvi Gupta said:
    And can we use 10K external resistor instead of 900k when VBUS voltage is 5V?

    This is not recommended.

    Please let me know if you have any other questions.

    Thanks,

    Ryan

  • 0
    TI__Guru** 123940 points

    Hi Purvi:

         the threshold on VBUS_DET should be around 450mv, but I will confirm with our system engineer.

    Best

    Brian

  • 0 in reply to Brian Zhou
    Prodigy 30 points

    Hi Brian,

    But the datasheet says, VBUS threshold range is Min - 2.95V, Typ - 3.3V and Max - 3.8V.

    Also what is the maximum voltage acceptable on "VBUS_DET" Pin? 

    Regards,

    Purvi

  • 0 in reply to Purvi Gupta
    TI__Mastermind 21775 points

    Hi Purvi,

    Purvi Gupta said:
    Also what is the maximum voltage acceptable on "VBUS_DET" Pin? 

    The maximum acceptable voltage is 4V. This is part of why VBUS_DET requires a 900KOhm resistor to ensure any voltage used for VBUS goes below 4V. 

    It is recommended to follow the datasheet recommendations as to the VBUS_DET pin.

    Thanks,

    Ryan