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TPS65981: Inconsistent Power Status Readings

Brendan Falvey
Prodigy 50 points
Part Number: TPS65981

In our device, we need to differentiate between high power ports and standard ports. I've been testing the I2C registers to ensure the main processor can access the cable attached and manage the system accordingly. However, I've noticed a discrepancy in the Power Status (0x3F) register when a USB cable is connected in Dead Battery mode versus when the TPS65981 is already powered on and mode is "APP".  For example, when I connect the device to a PC, the register readings return the following information:

Power Status 0x3F Dead Battery In App Mode
PowerConnection Connected Connected
SourceSink Sink Sink
Type-C Current USB DEF 1.5A
BC1.2 Detect Enabled Enabled
BC1.2 Status SDP SDP

The value for Type-C current is inconsistent in detection for the same connection to the PC. This happens for all modes relying on BC1.2 detection whether its a SDP or a DCP.  (I don't have a CDP port to test this case).

Could you please explain the discrepancy and how to fix this.

Also, there was a bug in the python script "register_definitions.py" At line 1369, the definitions for BC12Status_list are wrong

BC12Status_list = ['SDP', 'Res', 'CCP', 'DDP']

I fixed my script to read

BC12Status_list = ['SDP', 'Res', 'CDP', 'DCP']

  • 0
    TI__Mastermind 36756 points
    Hi Brendan,

    Thank you for pointing out that error in our GUI tool. I will make sure this is correct in the next release.
    As far as the dead battery vs normal boot from VIN_3V3 BC1.2 detection is concerned, can you let me know which BC1.2 charger you are using? Also, have you been able to reproduce this on our TPS65981EVM platform?

    Thank you,
    Eric
  • 0 in reply to Eric Beljaars
    Prodigy 50 points
    For testing, the results I posted earlier are from a typical USB port on my Dell desktop PC. The results are similar with the charger I use that doesn't provide PD mode. The Type-C Current will read 1.5A from dead battery, and 3A (correct) when powered from VIN_3V3. The charger is a Phihong USA model AQ15A-050A purchased through Digikey.

    I cannot reproduce the events on TPS65981EVM platform. The results are consistent across both modes.

    I figured the determination of Type-C Current outside of PD is based on an analog measurement. So I measured the value of LDO_3V3 in the two power modes. On our prototype, when running the part from VIN_3V3 (3.304V), LDO_3V3 measures 3.261V. And with VBUS (5V), the value is 3.329V. Could our board be taxing the load of the LDO_3V3 and affecting the sense measurement?
  • 0 in reply to Brendan Falvey
    TI__Mastermind 36756 points
    Hi Brendan,

    I don't think you would be taxing the LDO_3V3. However, what all do you have connected to that net outside of the SPI Flash and some resistor pull-ups/downs?
    What do you have BusPowerZ connected to? Are you sinking power on PPHV or PPEXT?

    Thank you,
    Eric
  • 0 in reply to Eric Beljaars
    Prodigy 50 points
    BUSPOWERZ is set to 1.63V (Res bridge off LDO_1V8). All power is sinking through PPHV.
  • 0 in reply to Brendan Falvey
    TI__Mastermind 36756 points
    Hi Brendan,

    Can you confirm if you have BC1.2 detection enabled once you have booted from dead battery mode?

    Thank you,
    Eric
  • 0 in reply to Eric Beljaars
    TI__Mastermind 36756 points

    Hi Brendan,

    Not sure if you were able to resolve this issue or not.

    If you were able to resolve it, can you please close this thread by selecting This resolved my issue

    Thank you,

    Eric

  • 0 in reply to Eric Beljaars
    Prodigy 50 points

    I was able to test the firmware on the evaluation board and the results were not duplicated there. With the evaluation board, the tests worked correctly and determined the correct condition on all conditions.

    This led me to review the prototype design and I found unintentional loading on the CC pins that would change between dead battery and system on mode. I was able to remove that loading and now my prototype works.

    Thanks for your help