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USB charge port configuration if 1A max. output

Barry Klein1
Intellectual 610 points
Other Parts Discussed in Thread: TPS2511

If my USB charger has a 1A maximum output what should my USB port connection indicate to the target device?  I see a lot of products with this output spec but the standards don't seem to focus on 1A maximum output - more like 500mA, 1.5A, and 2.1A.  So if the targets expect 1.5 or 2 A the charger likely overcurrent - hiccup or latch. And if 500mA - how to indicate that to the most typical targets without them failing on it and the product being rejected in the marketplace?  Seems most design/spec focus is on a host charger designed to cover all the load cases but what about for products where that is not cost effective or practical and current limitations are needed?

We have tried a few of the auto-configuration chips like the TPS2511 but they don't seem to cover the case where the host power is limited.

  • 0
    TI__Genius 13700 points
    Hello Barry,

    Just so I clearly understand your question.
    You have a USB source that can supply 5V @ 1A and you want to know how to communicate that to devices that are connecting into the USB Port for power?
    I will continue this post assuming that what I described above is correct if not please respond and correct me.

    Using a part such as the TPS2511 you would want to configure it as a SDP this decision is a result of the contents of Table 1 on Pg 11 of the datasheet for this part.
    When a USB 2.0 device is inserted it will communicate to the power controller and the port controller will say I am a SDP and since you are a USB 2.0 device that means I can support 500mA.
    When a USB 3.0 device is inserted will communicate to the power controller and the port controller will say I am a SDP and since you are a USB 3.0 device that means I can support 900mA.

    Both cases follow the accepted USB standard for 2.0 and 3.0 while negotiating the most current that the inserted USB device can understand given its generation of USB.

    You would then set the current limit of the TPS2511 to be 1A so that if a device does try to pull more than that much current it will protect the upstream source of the power.

    Hopefully that is your question and it answers it otherwise please help me understand by submitting a clarifying response.