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TPS65920 USB Low Speed mode pull-up still on D+ not D-

Mike Score
Expert 4110 points
Other Parts Discussed in Thread: TPS65920

Customer is not able to get the TPS65920 into low speed mode.   He got the device in high speed mode, D+ pull-up showing.  However, when he puts it into low speed mode the pullup does not change from D+ to D-.   The clock is on, the ID pin is shorted low for OTG mode, all LDOs active.  The ID comparitor is working. 

He is writing 0x46 to register 4 for low speed mode...  Is that correct?  Is there something else he needs to configure 1st?

He got 0x46 from:  4 is not suspend mode, and 6 is from Tx select =2, turn-on=1, Op mode=0 (from Table 14-17. D+/D– Termination Settings Versus Signaling Mode ) in the TRM.

-Mike Score

  • 0
    Intellectual 370 points

    Hi Mike

    I am just a bit confused regarding the observations you mentioned above.

    As D+ pull-up is observed in FS (full speed) mode and not in HS (High Speed) mode.

    Can you just re-check and confirm your observations.?

     

    Regarding LS (Low Speed) mode the TPS65920 supports only HOST operation please find the following steps.

    In addition to writing 0x46 to FUNC_CTRL (Reg 4) you have to write 0x26 to OTG_CTRL register (0x0A). Also note that it will not Pull-up the D- line.

    D- line has to be pulled by the external device connected to the USB interface of the TPS65920.

     

    Regards

    Ankit

  • 0 in reply to Ankit Somani15962
    Prodigy 155 points

    Hi Ankit, Mike,

     

    Regarding Ankit's answer - Indeed FS is chracterized by a PU on D+, but HS connection protocol also begins, as FS, with D+ pulled-up. Thus the D+ state gives us no true indication of whether the tranceiver is in HS or FS mode.

    I have the same issue with FS. I would like to connect my device to the PC as an FS device. How do I go about it? Writing 0x46 to register 0x04 does not work for me. After changing the register value I see no identification by the PC and cannot communicate with it.

    So, how can I enable FS connection to the PC?

    Thanks,

    Matan