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Original question:

TPS65987D: PP_HV1 as a Source Path

TPS65987D: Using PP_HV1 for 5V, 9V, 15V and PP_HV2 for 20V

Ivo Ninive
Prodigy 50 points
Part Number: TPS65987D
Other Parts Discussed in Thread: TPS55288,

Our application uses PP_HV1 for 5V, 9V, 15V and PP_HV2 for 20V. Both power paths are sourcing voltages out on a USB-C connector. PP_HV1 is sourced from TPS55288 buck/boost supply. PP_HV2 is coming from a fixed 20V rail in the PSU inside our product.

The max current for all voltages are 3A.

When testing compliance we see that the PP_HV1 path is not limiting the current when having an OC event. However, the PP_HV2 patch is limiting the current correcty. It limits the current at around 3.27A.

We have tried to swap the PP_HV inputs by applying 20V to PP_HV1 and 5V, 9V, 15V to PP_HV2. Then the PP_HV2 is not able to limit the current, while PP_HV1 is able. So the fault is not following the physical power path.

We are starting to believe that only the PP_HV path with the PDO1(5V) defined is able to limit the current.

Is there a limitation within the chip or could it be the TI config tool that is not mapping correctly to the internal registers? Maybe there are some settings in the config tool that indirectly is affecting this?

Our TI config tool project file can be found here:
https://drive.google.com/file/d/1GFdZ-axdV_NJeWKsa1EPiJpXm0qRie4D/view?usp=sharing

  • 0
    TI__Genius 12665 points

    Hi Ivo,

    Please see our email conversation for a response to this. I have copied it below as well:

    --------------------------------------------------------------------------------------------------------------------

    I did some analysis of the issue today and I believe I have found the cause of the OCP failure to be with the PD controller’s firmware OCP function, which is only used for greater than 5V sourcing. When sourcing 5V, the PD uses an overcurrent clamp circuit to limit current. Can you let me know which version of the TPS65987D firmware you are using? In earlier versions of this TPS65987D firmware, we did not have any firmware OCP function implemented.

    Please see below for a detailed description of our observations so far and what I believe is happening:

    The TPS65987D will perform current limiting or trigger overcurrent protection shutoff in 2 ways:

    1. When the source voltage of the PD is 5V, the PD limits the current using the IOCC overcurrent clamp in hardware.
    2. When the source voltage of the PD is greater than 5V, the PD performs overcurrent protection in firmware only and does not use the hardware overcurrent clamp.

    What you seem to see in terms of overcurrent protection behavior seems to be in 3 categories:

    1. On PP_HV2, the DC/DC converter is limiting the current to ~3A.
    2. On PP_HV2, when you connected the 5V to USBC_ADJ, the PD uses its IOCC overcurrent clamp circuitry to limit the current to ~3A.
    3. On PP_HV1, for a 20V sourcing contract, the PD does not limit the current or trigger overcurrent protection but the PSU does.

    What I believe is the issue is that the TPS65987D’s firmware overcurrent protection (only used for greater than 5V sourcing) is not working on either power path. When sourcing 5V-12V, the DC/DC converter is limiting the current using its own clamp circuit. When sourcing but with 5V connected to USBC_ADJ, the PD’s overcurrent clamp circuitry is limiting the current. When sourcing 20V, the PD’s firmware overcurrent protection is not working, so no overcurrent function is seen. Please let me know what version of the firmware you are using.

    Best,

    Alex