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TUSB2077A: Issue with PORTPWR and PORTDIS pins

Clement Soucy
Prodigy 20 points
Part Number: TUSB2077A

Hello,

I have issue with PORTPWR and PORTDIS pins. I have attached the schematic sheets related to it. I want to use LEDs on those pins for troubleshooting the product in the field. The behavior of the LEDs does not seem to respect the description in the device datasheet. More precisely:

1. D22 flash a couple of times during and stays OFF after the first short-circuit on any downstream port (any between port 1 to 6 in my case). I was expecting D22 to stay ON because at least 1 other port is powered after the short circuit. D22 is ON before first short circuit.

2. D21 stays ON even after all 6 downstream ports are disabled after short circuits. I was expecting it to turn OFF right after the first short circuit.

3. D20 and D21 flash a single time after I connect the upstream port. After that, as described in #2, D21 stays ON and D20 stays OFF. I was expecting D20 to turn ON after the first short circuit.

I have confirmed that the USB output voltages are 0 V after short circuits. Problems #1 and #2 are observed when the upstream port is connected (and detected by the computer). I have no USB communication issue using my circuit.

Have I misunderstood the device datasheet? Have you seen this behavior before?

Best regards,

ClementSupport for TI Hub.pdf

  • 0
    TI__Guru 60870 points

    Hi Clement,

    PORTPWR is going low since an overcurrent was reported.  Do the other ports stay powered on?  Typically the USB host controller will power off all hub ports after an overcurrent event is reported.

    PORTDIS is not going low because none of the ports are disabled.  While the hub port is powered off due to overcurrent, this is not the same as the port being disabled per USB protocol - you can see section 11.24.2.7 of the USB 2.0 spec for more information on the hub port status registers.

    Regards,

    JMMN

  • 0 in reply to JMMN
    Prodigy 20 points

    Hello JMMN,

    I understand, I misunderstood the datasheet. However, I think there should be clarification in the datasheet at page 5. Especially for PORTPWR pin, which does not do what is written there. When I have devices powered up and overcurrent on single port, it goes low. It should be "When any port is powered off, PORTPWR goes low".

    To answer your question, when I create an overcurrent on a single port, only this port is powered off and the others are still powered ON. This is what I needed, hence the individual power management in the schematic.

    So for troubleshooting in the field, I will add an antiparallel red diode to D22.

    Regards,

    Clement