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  • TI Thinks Resolved

TPD3S044: Managing power for a Self powered device/Bus powered Device/USB Host

Part Number: TPD3S044

I tried to put this question in the USB forum but once you select the TPD3S0x4 then the forum is hard wired. It's not a circuit protection question. Well it is and it isn't.

I'm working on a device which may operate as a USB Host, in which the device is powered by a DC/DC converter and 5V could be switched to the USB Bus with a TI TPD3S0x4. 

However the device can also operate as a USB Device, both self powered and USB Bus powered. This is all on a single USB interface of a uC which can be configured for the USB Mode of operation. The TPD3S0x4 only solves the Host configuration. If the device is acting as a USB Device and is self powered I assume I'd have to isolate the device's power from the USB Bus and be in self powered USB Device mode. If however the device is acting as a USB Device but powered from the USB Bus in that case you'd want the device's 5V Rail connected to the VBus of USB Bus.

I'm wondering is there a single solution to this problem, or is this a case of switching transistors to detect and manage the USB Power? If anybody knows of an IC which could mange all power requirements that'd be great.

  • John,

    You will need to implement a VBUS power mux to ensure that your system works correctly for both the HOST mode using the TPD3S0x4 and for Device mode where you would be best served to add a USB power switch from the TPS20XX family. I cannot suggest a specific switch without knowing your system's current needs. For a 500mA system, I would recommend the TPS2041B as a good starting point.

    You will have to control the #EN lines of the two power devices depending on the mode of operation. They both support wired or type pulldown logic so you can use supply detectors or other logic to build the power safe enable logic.

    If you can provide me some more detail about your system, I will be happy to help you with part selection.

    Please reply to this thread with any further questions.

    Chuck
  • In reply to Chuck Branch:

    Hi Chuck, thanks a million for that suggestion. I'm not sure that chip would work as you have to actively switch. I'm still going through it. As I'm dealing with USB2.0 it's only going to be sourcing 500mA in Host mode, to a single connected device, or in device mode be sinking 500mA from the USB VBus. I did find an interesting thread on stack exchange which mentioned some interesting devices.

    In that post the basic circuit I was thinking of is in the initial question but then a few interesting options are mentioned in the post. The LTC4417 looks interesting on the surface but it's got a large pin count and size. Probably cost as well if I looked at it. However it certainly doesn't simplify the design at all and I think at present the best solution is the BJT circuit.

    I did find another product which selected between two power inputs and prioritised one of those inputs. That sounded great but again had a rather large pin count and price tag. I just assumed that there had to be an integrated solution but the BJT seems to be the way to go.

  • In reply to John Whitmore:

    John,

    If you need to or two power supplies together in your system, you might consider this part www.ti.com/.../tps24741.

    I am not sure if it meets your needs, but it is similar in function to the circuit you described.

    Regards,
    Chuck

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