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TPS65982 EVM - role of the bucks on the sink side

O'Mellin
Expert 6005 points
Other Parts Discussed in Thread: TPS65982, TPS65982-EVM

hi all,

               Quick description of the question: customer uses 2 EVM as source ID 2 and sink ID 7. Everything works as expected except that customer was surprised to see 12V on the sink side at external power with J6 unpopulated. Therefore they removed the inductor of the external buck, and nothing works.

                They are worried of the role of the buck to get the EVM to work as they did not intend to have bucks on the sink side, only the TPS65982. Also can you please confirm that only the 2 external fets are required for the sink to support 20V/5A?

Thanks

  • 0
    TI__Expert 5110 points

    Hi Olivier,

    Is the system using PP_EXT or PP_HV for sink path?

    Regards,

    Atiq

  • 0 in reply to Atiq Rahman
    TI__Expert 6005 points

    Atiq,

    Not sure I understand your question. on the sink side power comes from VBUS and J6 being unpopulated and voltage remaing at 12V or under, PP_EXT FETs should not be involved.

    please call me to accelerate this.

    O'mel

  • 0 in reply to O'Mellin
    TI__Expert 5110 points

    On the sink side one path needs to be configured as input to sink power from VBUS. Like in below example PP_EXT is configured for input. In the experiment you mention, do you know which path is configured for sinking power? 

  • 0 in reply to Atiq Rahman
    TI__Expert 6005 points
    Atiq, I guess it's PP_HV but i'll get confirmation of that. Do you mean there is a path between HV_source and external power without J6 jumper?
    what are the roles of the bucks on the sink side when no tiva board is present except light up the leds?
  • 0 in reply to O'Mellin
    TI__Mastermind 30280 points

    O'Mellin,

    Hopefully we can resolve this problem with a more structured approach to debugging.

    Since RPD_G1/2 are tied to CC1/2 by default on the TPS65982-EVM, this means Dead Battery Mode is automatically supported (assuming no PCB modifications have been made).

    Regardless of the FW Config ID #, the Sink FET path will be enabled for a Type-C connection on either PP_EXT or PP_HV based on the BUSPOWERZ setting (tied to GND by default because S2 is un-populated, meaning PP_EXT is enabled in Dead Battery Mode).

    As long as the Barrel Jack is not applied at J4, only BUSPOWERZ will matter for your tests (the TPS65982 will remain in Dead Battery Mode). The FW, once loaded, cannot modify the Sink FET path enabled by BUSPOWERZ while the EVM remains in Dead Battery operation.

    The voltage on VBUS will depend on the capabilities of the Source board you are connected to via the Type-C cable. I would advise marking an EVM as the 12V PD Source with a piece of electrical tape to ensure it is not swapped out for an EVM that does not have Source capabilities.

    Assuming the Source EVM is static and the Config ID # of your Sink EVM is un-changed (S1, switches 1-4), VBUS should always resolve to the same voltage after USB PD negotiation (ideally, 12V in your test).

    If you measure the voltage for the last 6 columns of the table with a multimeter while testing, we should have a clear picture of what is happening.

    • SCOPE SHOTS of VBUS, PP_EXT, and PP_HV would be preferred
    • PHOTOs of your Sink board showing the S1 switches and J6 jumper can also be helpful.

    Test Case

    #

    Cfg B3

    (S1,4-5)

    Cfg B2

    (S1,3-6)

    Cfg B1

    (S1,2-7)

    Cfg B0

    (S1,1-8)

    BSPWRZ

    S2 (4-5/6)

    J6

    on?

    VBUS

    (TP3)

    PP_EXT

    (J6,1)

    PP_EXT

    (J6,2)

    PP_HV

    (J5,1)

    PP_5V0

    (J5,2)

    VIN_3V3

    (J5,3)
    1 0 1 1 1 GND Yes - - - - - -
    2 0 1 1 1 LDO_1V8D Yes - - - - - -
    3 0 1 1 1 GND No - - - - - -
    4 0 1 1 1 LDO_1V8D No - - - - - -

    When J6 is installed, I expect that the LEDs will be operational and a voltage close to VBUS voltage will be present at PP_EXT & PP_HV.

    When J6 is NOT installed, I expect that the LEDs will off when the PP_EXT Sink path is used (J6, Pin 2 = VBUS) and PP_HV will be approaching 0V as the bulk caps discharge.

    Whenever the PP_HV Sink Path is enabled, all results other than VBUS & PP_HV should be ignored, because the EVM is technically a Source from a HW standpoint and reverse operation of Buck regulators is not relevant.