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Original question:

TUSB321: TUSB321 not detecting cable inversion

TUSB321: VBUS_DET and DIR problems

Ben Johnson1
Prodigy 20 points
Part Number: TUSB321

Hello,

We have 2 problems

1.  We've had some confusion on the TUSB321 VBUS_DET pin and the voltage thresholds discussed in the datasheet.  In some places (ie 6.1 Absolute Maximum Ratings)  VBUS_DET allows from -0.3 to 4.0V.  Other places (ie 6.3 Recommended Operating Conditions) where the VBUS_DET threshold voltage is described as 4.0V, which indicates to me that the voltage needs to exceed 4.0V in order to be detected).   There appears to be 2 different definitions for VBUS_DET, where one means the pin itself, and the other means the "5- to 28-V VBUS input voltage" on the other side of the RVBUS (909k resistor)

2. I cannot find any indication for how the DIR logic works in conjunction with TVBUS_DB.  I think that the CC1 and CC2 pins are "polled" just after TVBUS_DB times out, which would indicate that if VBUS_DET was not connected, or did not change, then no changes on CC1 and CC2 would be detected, and no change would happen on the DIR pin.

  • 0
    TI__Guru 64326 points

    Hi Ben,

    1. You are correct, VBUS_DET absolute maximum ratings refer to the voltage seen on the VBUS_DET pin itself. The VBUS_DET threshold voltage refers to voltage seen on the other side of the R_Vbus resistor connected to Vbus on the type-C connector. 

    2. This depends on the PORT type can VBUS_DET has no meaning in DFP. DIR is actually determined when a correct CC voltage is detected and debounced. 

  • 0 in reply to Malik Barton57
    Prodigy 20 points

    Thanks Malik!

    For a little more clarification then...  In UFP mode, after the VBUS_DET has been debounced, that is when the CC voltage is "sampled" to determine DIR?  What happens if CC changes sometime later?

    Thanks,

    Ben

  • 0 in reply to Ben Johnson1
    TI__Guru 64326 points

    Hi Ben,

    Yes, VBUS denounce comes first then DIR is determined. In a typical connection the CC voltage will not change later unless there is a full disconnect.