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TPS65987D: CC changes from Rd to Open when VBUS changes to Off

Takumi Egawa
Prodigy 100 points

Part Number: TPS65987D
Other Parts Discussed in Thread: TPS65987,

Hi,

We use TPS65987 as a self-power Sink device.
It seems to make CC changes from Rd to Open when VBUS changes to Off.
Is it possible to avoid this behavior by changing the FW?

Our Host device monitors whether CC-pin is terminated with Rd even when Host does not output VDD. 
We want CC of TPS5987D is always terminated with Rd.

Regards,
Takumi
  • 0
    TI__Genius 9370 points

    Hi,

    Thanks for reaching us. I'll get back to you by tomorrow. 

    Thanks
    Prajith 

  • 0 in reply to Prajith Cheerakkoda
    TI__Genius 9370 points

    Hi,

    I can see 87 EVM presenting Rd irrespective of Vbus. I connected Rp (56K pulled to 5V) directly to CC and can see terminated voltage on CC. 

    Hope you are also performing the same test. if yes, please share the scope trace. BTW, are you testing this on EVM?

    Thanks
    Prajith 

  • 0 in reply to Prajith Cheerakkoda
    Prodigy 100 points

    Please check the attached scope traces.
    Ch1=CC, CH2=VBUS

    In regards to the first trace, TPS65987D requests 5V and enters DPAltMode.
    Then Source stopped supplying VBUS and Vconn,
    In this case, TPS65987D presents Rd and voltage is divided into Rp and Rd.

    In regards to the second trace, TPS65987D requests 12V and enters DPAltMode.
    Only the PDO is diffrent.
    After Source stopped supplying VBUS and Vconn, CC voltage changes to 3.3V for 150ms.
    Then, CC voltage reverse to divided voltage.
    I think this is because Rd changes to Open and CC is pulled-up by Rp(3.3V)

  • 0 in reply to Takumi Egawa
    TI__Genius 9370 points

    Hi,

    I believe UVP = 50% in your project file, that's why CC line goes to 3.3V in the middle of Vbus transition (12V-.0V). Here the disconnect happens due to the PD controller entering Error Recovery triggered by UVP. Looks like this a self powered device, it takes 150ms to present Rd.  

    Thanks

    Prajith