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TPS65981: TPS65981 Transmit Source Capabilities - Maximum Current setting

GerryP
Prodigy 160 points
Part Number: TPS65981
Other Parts Discussed in Thread: TPS25820, TPS25810

Hi,

I am using the TPS65981 to charge a Samsung S3 tablet whilst the tablet (as a DFP) establishes a USB2.0 connection with an FTDI FQ232R device (as an UFP).

I am trying to define the Transmit Source Capabilites in the TPS6598X customisation tool so that the maximum current is less than 0.5A. However, I'm finding that reducing the maximum current, say to 250mA, doesn't change the charging current for the tablet. I don't have a PD analyser to check what the power negotiation steps are. Should it be possible to define the maximum current to be less than 0.5A?

  • 0
    TI__Mastermind 36751 points

    Hi Gerry,

    You can read back your negotiated PD contract using the TPS6598x application customization tool when entering Debug mode. Just a question from my end: Why would you use PD to charge at less than 500mA? PD is used to negotiate power at higher levels offered by standard USB. If you just need standard USB charging currents, you can consider using the TPS25810 or TPS25820.

    If this answers your question, PLEASE select This resolved my issue

    Thank you,

    Eric

  • 0 in reply to Eric Beljaars
    Prodigy 160 points
    Hi Eric,

    Thanks for the suggestion. Our application is slightly strange in that the TPS65981 is part of s system that is battery powered itself and we want to see if we can reduce the charging to the tablet to "trickle charge" it below 500mA to save the TPS65981 system battery. If the TPS65981 is capable of supporting a source capability of less than 500mA, it is a case that the tablet can override that and take 500mA anyway?

    Best regards,

    Gerry
  • 0 in reply to GerryP
    TI__Mastermind 36751 points

    Hi Gerry,

    Per the USB Type-C spec, a Type-C port that supports USB 3.1 data rate needs to supply 900mA. A USB Type-C port that only supports USB 2.0 needs to supply 500mA. The TPS65981 is following this spec and cannot offer less than those current levels based on the supported data rates.

    If this answers your question, PLEASE select This resolved my issue

    Thank you,

    Eric

  • 0 in reply to Eric Beljaars
    Prodigy 160 points
    Thanks Eric, that clarifies that point.

    Best regards,

    Gerry