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TPS25750: Possible to source 5V via the BQ part instead?

Eric Castle
Intellectual 710 points
Part Number: TPS25750

Hello,

If I understand correctly, for a sink/source configuration (default in the config tool, as shown below), then the 5V/3A PPO is sourced via the 5V regulator, and not from the BQ. Is there a way to change this in the configuration tool? I can still have 5V attached (supplying up to ~1A), but in our current design our 5V regulator cannot handle the total worst-case current draw, whereas the BQ has access to the cells in the pack. This would simplify our design if we could just always use the BQ for sourcing output current. 

Thanks,

-Eric Castle

  • 0
    TI__Genius 12895 points

    Hi Eric,

    Yes, this is possible by switching the 5V 3A PDO power path from the default PP5V to PP_EXT. This would be done in the 0x32 TX Source Capabilities Register. While this capability is supported by the TPS25750, it is not currently supported by the web GUI. 

    To change this setting, you would need to use an embedded controller EC to write to the 0x32 TX Source Capabilities register with the correct data bits. 

    Byte 2, bit 1:0 should be set to 10b (PDO1 is the 5V contract). This would set PDO1 to use the PP_EXT1 power path which connects to the BQ part on our EVM. This would need to be written to register 0x32 on the PD controller along with the proper PDO1 contents as specified in the technical reference manual available on ti.com.

    Note: All PDOs above PDO1 can only use PP_EXT1 power path running through the BQ part. That being said, using PDO1 is still mandatory for boot up.

    Best,

    Alex

  • 0 in reply to Alex Liu
    Intellectual 710 points

    Thanks for the info Alex!

    However, we tried that today, and were unable to get that to get it to work. We tried the following:

    Solution 1) Write to register 0x32 to adjust PowerPathForPDO1 to 01b, and then send the 'SSrC' command. At that point, the device failed to be detected by our USB-C load.

    Starting over:

    Solution 2) Adjust PDO1 to 1A max, and add another 5V PDO at 3A (as any later PDOs will automatically source from PP_EXT1). The load detected the device, and the new PDO appeared in the list, but selecting it caused the TPS to reset.

    Any thoughts on what we're doing wrong?

    Thanks,

    -Eric Castle

  • 0 in reply to Eric Castle
    TI__Genius 12895 points

    Hi Eric,

    Are you using TPS25750D or TPS25750S? The D version has two internal power paths while the S version has one internal and one external power path. In the D version TPS25750D, you cannot change the PDO1 power path to source through PP_EXT1 even by writing to the register. PDO1 must use PP5V. For the TPS25750S, this is possible. 

    I consulted with the team about using two 5V PDOs, with PDO1 being 5V through PP5V and PDO2 being 5V through PPHV or PP_EXT1. However, this is not allowed by the PD controller firmware.

    Please check if you are using TPS25750D or S.

    Best,

    Alex

  • 0 in reply to Alex Liu
    Intellectual 710 points

    Hi Alex,

    Thank you for that clarification. Yes, we're using the D part currently (the EVM reference design), which explains why this doesn't work. 

    So, if I understand correctly, we could switch to the S version and add some external FETs and then we could switch the part to source 5V via PP_EXT1?

    Thanks,

    -Eric Castle

  • 0 in reply to Eric Castle
    TI__Genius 12895 points

    Hi Eric,

    Yes, you are correct. The S version EVM has this external switch on the board. If you are designing your own system you will need to add this external switch PP_EXT1.

    Best,

    Alex

  • 0 in reply to Alex Liu
    Intellectual 710 points

    Hi Alex,

    Does TI have any reference designs using the S version? We based our current design using the EVM, with the D version and the BQ25792RQM.

    Thanks,

    -Eric

  • +1 in reply to Eric Castle
    TI__Genius 12895 points

    Hi Eric,

    There is an example schematic and layout tips for TPS25750S on the TPS25750 datasheet, under the "TPS25750S - Layout" section. 

    While I do not believe we have an official reference design for the S version, you can follow the information in the datasheet for TPS25750S.

    4861.tps25750.pdf

    Best,

    Alex