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TUSB4041I: Hub Power distribution switches - do I really need them on every port?

Mike Nudelman
Intellectual 265 points
Part Number: TUSB4041I
Other Parts Discussed in Thread: TPS2001C

I am making the hub that should take the power from one of the devices and supply it to other devices and the OTG host (Raspberry Pi).

Only one of the devices is hot-pluggable (a memory stick), the rest are permanently plugged in inside the box and are not hot-plugged.

None has a battery.

I have used the TUSB4041I EVM board as the ref design. 

So,

1. I think I should not be using the Power distributor (TPS2001 in my case) on all the device ports, considering one of them supplies the power.

2. Do I really want the Power Distributor on any device that is just a 5V USB device without battery and not hot-plugged?

3. I probably should use one on the external pluggable memory stick for short protection? 

So I only need one of the TPS2001, not four?

Any advice?

  • 0
    TI__Guru 64326 points
    Mike,

    I believe you would want to use TPS2001C or other power switches for over-current situations with 5 V USB devices even if they have no battery and are not hot-plugged. This is to protect the permanently plugged devices. If you are sure the permanently plugged devices can tolerant current spikes from the power source (hot-pluggable device) then a power switch may not be needed however without a power switch the USB OTG host will not be able to turn off downstream port power when necessary. I recommend use of a power switch on every device.
  • 0 in reply to Malik Barton57
    Intellectual 265 points
    Malik

    My hot-plugged device (power source), the controller board (it's been historically a device so I have to work with it; else I would make it a master) provides 5V @3A max protected by a resettable fuse of 2.6A. So I think by itself it won't create any current spikes. The one that could is the other hot-pluggable device, a memory stick. I am using a TPS2001 on it. Wouldn't this protect the power source from spikes?
    I also use some capacitors, 10uF per port plus some bulk to mitigate the spikes (again, other devices other than the power source ones use short 12" permanently plugged cables).
    I do not have any need for the OTG Master to turn any devices On or OFF, as even though it is the Master (again, only for the historical reason of the Controller being a device) it is function-wise is a mere display, based on Raspberry Pi, and since the Pi wants to see everything as devices, hence the configuration, but I do not want it to turn anything Off.

    BTW do I need the EEPROM? I want the operation to be as basic as it gets.
  • 0 in reply to Mike Nudelman
    TI__Guru 64326 points
    Mike,

    In this case it may be fine to use only one power switch but this is not compliant with USB spec.

    A EEPROM is not needed for default operation of TUSB4041.