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TPS65988DJEVM: Best way to get PD Source/Sink from BQ battery charger to both ports

Ben Osorio
Prodigy 10 points
Part Number: TPS65988DJEVM

Most of the Ti reference designs use PPHV1/2 for the fixed SYSTEM_5V rail for Sourcing power, and the external powerpaths (controlled by PP_EXT1/2) for PD sink to the BQ charger. 

Instead, can I use PPHV1/2 for PD Source & Sink to BQ charger, and load switches (controlled by PPEXT1/2) to Source SYSTEM_5V to VBUS? 

Is there any reason NOT to do this? 

Does the GUI have options to support this configuration?

Thanks

  • 0
    TI__Genius 12665 points

    Hi Ben,

    The two integrated internal PPHV power paths have bidirectional switches so they can be used to source and sink as you prefer.

    The PP_EXT 1/2 power paths are default used to sink but can be configured to source through the VAR DC/DC. In 0x27 Global System Config register, PP3 and PP4 are the external power paths on the EVM. You can set one or both of these to source only. Then set PP1 and PP2, the internal power paths, to source and sink. You must also configure the sink PDOs in 0x33 TX Sink Capabilities register to sink using PP1 or PP2. If you want to source 5V on the external paths, configure the 5V source PDO in 0x32 TX Source Capabilities register to source using PP3 or PP4.

    Using this configuration should be ok. We just chose to configure it differently in the EVM by default. I would recommend setting one of the external power paths (PP3 or PP4) as sink and source to ensure you can sink power in dead battery mode.

    Best,

    Alex

  • 0 in reply to Alex Liu
    Prodigy 10 points

    Hi Alex

    Per Table 8-8 Dead Battery Configurations, would one of these three config options (BP_WaitFor3V3_Internal, BP_ECWait_Internal , or BP_NoWait) take care of the dead battery condition without using the external power path as sink?


    I ask because the load switch I want to use on external power path is not bidirectional. 

  • +1 in reply to Ben Osorio
    TI__Genius 12665 points

    If you can wait for the PD to start up before sinking then it will be ok even without those config options. BP_WaitFor3V3Internal can be used to enable the internal PPHV for the port sinking power before the PD starts up fully. 

    One correction on my above answer. You can only sink using the internal PPHV power paths if the variable DC/DC converter you use is bidirectional. While the PPHV switches are bidirectional, the variable DC/DC converters on the EVM are not bidirectional. They can only source, not sink. This is why we use the external paths to sink. But you can do this in your system with a variable DC/DC and the proper circuit.

  • 0 in reply to Alex Liu
    Prodigy 10 points

    Perfect.

    Thanks Alex