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USB Power Distribution switch Current limit thresholds .....!

malli arjun1
Intellectual 610 points
Other Parts Discussed in Thread: TPS2041A, TPS2041C

Hi..,

for one of ours USB HUB solution, we are trying evaluate the Power switches. I have basic doubt regarding this.

from my knowledge, USB2.0 allows a peripheral to consume max of 500mA . correct me if i am wrong.

Most of the switches like TPS2041A... states continuous allowed current is 500mA which is compliant to USB2.0.,

But the electrical characterstics says Current limit will be min = 0.67A, Typ = 0.85A and Max =1.01A. what are the conditions for these 3 ratings. if it alows 1A current to pass through without issing Over Current, this is violating USB2.0...

  • 0
    TI__Expert 7990 points

    The USB2 spec calls for the source to supply a minimum of 500mA.  Practically speaking, a system design would allow for some margin between the loading and sourcing.  Some loads such as disk drives are well known to draw peak currents over 500mA.

  • 0 in reply to Martin Patoka
    Intellectual 610 points

    there is no data in USB2.0 spec regarding these peak currents. Please correct me if i am wrong. if peak currents are taken also they will be taken for very short durations. I have seen in most datasheets the Over current contnious until the device enters Thermal shutdown or Current limit threshold( which is very higher than 0.5A, it has min, typ and max also, even i am not sure what these min,typ and max specifcations for Current limit and what are the conditions for min, typ and max) crossed.

    Sorry for the late reply. I can't able to track this message. it is not coming to my mail.....

  • 0 in reply to malli arjun1
    TI__Expert 7990 points

    I don't understand your question.  Please provide a specific question about a specific part.

  • 0 in reply to Martin Patoka
    Intellectual 610 points

    My question is general question related to USB Power distribution switches.

    The values mentioned in Qtn are related to TPS2041C. I am attaching a snippet from datahsheet regarding Over Current limit by the part.

    for 0.5A part, 

    my qtns

    1. Current limt has 3 values(min,typ,max) with large variation, which value has to be taken under what conditions(max value should be taken under what conditions)

  • 0 in reply to malli arjun1
    TI__Intellectual 2795 points

    (1) Current limit has tolerance, so it has min/typ/max,  this is because corner case, such as  the process, operation voltage and temperature shift.

    (2) As martin point out, USB2.0 request maxium allowable current drwan by porttable device is 500mA, so the power siwtch for USB2.0 application, minimum current limit must exceed 500mA and has some margin.

    (3)  For maximum current limit, it is better make sure  your front end dc-dc converter has  bigger current capacity, so that, power switch would limit the current when over-load or hot-short happen, and your front end dc-dc converter would not see it and be protected.