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TUSB8043: Questions about USB HUB design

Josue Osses
Prodigy 40 points
Part Number: TUSB8043
Other Parts Discussed in Thread: LP3470

Hello from Chile,

I am designing a USB hub with TUSB8043 and I have some questions.

I am not using the power switch to control the power of the low ports. Can I connect them directly to 5 [V]?

The pins FULLPWRMGMTz, SMBUSz / SS_SUSPEND and GANGED are disconnected. it's okay?

GRSTz is only connected to a capacitor to GND, how can I make VDD stable to a minimum of 10 μs before the VDD33? I do not really understand Timing Requirements well. I hope you can help me, thanks

  • 0
    TI__Guru 60865 points
    Hello Josue,

    Yes, downstream port power can be connected directly to 5V. In this case the FULLPWRMGMTz pin should be pulled high to indicate to the host that the hub does not implement full power management of the downstream ports. Also, it is recommended that you still have overcurrent reporting enabled in the hub even if the downstream ports are not power managed.

    It is ok to leave SMBUSz and GANGED disconnected.

    For GRSTz timing, make sure that the 3.3V and 1.1V rails ramp simultaneously or 1.1V before 3.3V. This is because the GRSTz internal pullup is connected to the 3.3V rail. If 3.3V ramps before 1.1V, GRSTz will already be pulled up before the device is fully powered. You can adjust the capacitor value to increase the reset if needed.

    Regards,
    JMMN
  • 0 in reply to JMMN
    Prodigy 40 points
    only one capacitor is needed? I was thinkin in a active reset using LP3470 in GRTS. Is that ok?
  • 0 in reply to JMMN
    Prodigy 40 points
    Respect to the FULLPWRMGMTz, datasheet says: "Can be left unconnected if full power management and SMBus are not implemented."
    You says to pull up it, so what do I have t do?

    Thanks!
  • 0 in reply to Josue Osses
    TI__Guru 60865 points

    Add a 4.7K pullup resistor to 3.3V to change the setting.

    Regards,

    JMMN

  • 0 in reply to Josue Osses
    TI__Guru 60865 points
    Yes, active reset is also a good solution and easier to control that a passive reset circuit.

    Regards,
    JMMN
  • 0 in reply to JMMN
    Prodigy 40 points
    datasheet says: "Can be left unconnected if full power management and SMBus are not implemented."
  • 0 in reply to Josue Osses
    TI__Guru 60865 points
    Hi Josue,

    Ok, the datasheet is not very clear. It would be better to say: Can be left unconnected if full power management is implemented and SMBus is not implemented. In this case, you are not using SMBUS mode and you are not implementing full power management so the pin needs a pull-up.

    Regards,
    JMMN