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USB Charging

297925
Prodigy 80 points
Other Parts Discussed in Thread: TPS65950

 

Reading all community info and datasheets i get the impression that it is possible to use USB charging (using the TPS65950) at 1.7A.
But it seems to me that the advised Tusb FET cannot handle the linear regulating dissipation.

Am i wrong?

Is there anyway to use the USB Charging Specification 1.1 with the TPS65950?

 

 

  • 0
    TI__Genius 15100 points

    Hi,

    Yes, you can use USB charging for maximum charging current.

    The recommended FET can handle dissipation. Can you please elaborate your concern about FET dissipation specs.

     

    Regards,

    Gandhar.

     

  • 0 in reply to Gandhar Dighe
    Prodigy 80 points

     

    Maybe i'm too straigt forward here,

    Well, let's suppose an empty Li+ battery with a voltage of 3.5V, the FET would have to dissipate (5Vusb - 3.5Vbat) * 1.7A = 2.55W
    In my case i need the 1.7A continuously for my system, and if my system at a point does not require the 1.7A, the battery should use this current.
    So pulsed charging mode wil not work.  The absolute maxium rating for the advised FDJ1027P fet is 1.5W.

    Also when trying to pull this current from a USB OTG plug (USB Charging Spec) i've noticed that the ID resistors TI describes (CEA) differ from the USB Charging Spec. Are the ID resistors only targeted at carkits?

    Thanks Gandhar, for the quick reply.

  • 0 in reply to 297925
    TI__Genius 15100 points

    Hi,

    In this particular case you will have to ensure that the software manages the current such that the FET specs are not violated. The best way to charge the battery is to use the default charging, in that case you will not have to worry about the power dissipation.

    If we are moving away from the default settings then as you pointed the FET should be the one which can handle the dissipation. If you have an external charger then you can limit the charger so that the current will not exceed a certain amount. If you know that you will need the maximum current and keep the same FET then some intelligent should be added in the software to handle this or you can have FETs with higher dissipation. Please ensure that the other parameters of the FET (especially the Rdson) are similar.

    I hope this information helps. Thanks for pointing this glitch in the external components used.

     

    Regards,

    Gandhar.