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TUSB319-Q1: VBUS_DET function clarification

Patrick Hewette
Prodigy 30 points
Part Number: TUSB319-Q1

Tool/software:

Support Team - my Assigned Focus Account has the follow question to clarify VBUS_DET operation...

                We need a bit of clarification on the VBUS_DET. The verbiage of

 

VBUS_DET being below the values in the table when the device is assuming vSafe0V connector voltage. It sounds like it is checking for a source being on the connector or maybe some residual capacitance that needs to finish bleeding off in the customer phone before it turns on the ID pin.

 

Am I reading this correctly? Can you provide any further clarity?

  • 0
    TI__Mastermind 38655 points

    Hi Patrick,

    The TUSB319-Q1 monitors VBUS via the VBUS_DET pin in order to determine whether the VBUS voltage being supplied exceeds what is allowed or not. If the VBUS_DET pins sees a voltage that exceeds VBUS(thr), then it will assume this voltage is not safe to be used for VBUS, and will not make the connection.

    If the VBUS_DET pin sees a voltage below VBUS(thr) and sees a connection on the CC lines, then the device will assume VBUS is at a safe level, and will allow the connection with the UFP to be made, letting the ID pin go low.

    Please let me know if you have any other questions.

    Thanks,

    Ryan

  • 0 in reply to Ryan Kitto
    TI__Intellectual 2095 points

    Ryan,

    In this particular situation the customer would like to ensure Vbus threshold is below 3.3V so it can detect legacy USB PD sources that could back feed at 3.3V.  The datasheet has the maximum limit of Vbus threshold at 4.2V when using a 900K ohm resistor.  Can they lower the resistor value on Vbus_DET to 700K ohms to lower the detection limit?  If not, how can the VBUS threshold be lowered below their required 3.3V limit?

    Thanks,

    Mark

  • 0 in reply to Mark Dahlman
    TI__Mastermind 38655 points

    Hi Mark,

    Just want to confirm, you are looking for a way for VBUS_DET to detect when a VBUS of less than 3.3V and prevent a connection from being made, as this will prevent PD sources from being back fed, correct?

    If you wanted to make VBUS_DET more sensitive to the voltages coming in at VBUS, yes, you could try using a lower resistance for VBUS_DET, like 700KOhm. This could cause lower and higher voltages to exceed the threshold for VBUS_DET, thus causing the ID pin to not be set low as easily.

    You could also do the opposite by setting the resistance for VBUS_DET higher, causing lower voltages to stay below the threshold of VBUS_DET, while higher voltages may be within that threshold.

    If you are aiming for only lower-voltages to be within the VBUS_DET range, thus setting the ID pin low, I would recommend using a lower resistance, like you suggested. Just keep in mind, this may cause higher voltages for VBUS, like up to 28V, to go to the VBUS_DET pin, which may damage it if they are not lowered enough by the VBUS_DET resistor.

    Thanks,

    Ryan

  • 0 in reply to Ryan Kitto
    TI__Intellectual 2095 points

    Hi Ryan,

    You are correct, I'm looking for a way to detect when VBUS is 3.3V or higher to prevent a connection being made.  I'll use the lower resistor value.

    Thanks,

    Mark