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TPS65981: UFP Power Sink Setup

Daniel Neasmith
Prodigy 40 points
Part Number: TPS65981

Hello,

I’m looking for some help debugging a design that uses TPS65981ABIRTQR. The intended setup is to have it as a UFP Power Sink which controls an HD3SS460IRHRT and acts as a mux for SBU and USB 2.0 lines.

Design: See below pictures

Issue: When we connect it with a DFP Source, the VBUS voltage oscillates between 1.1 V and 0.5 V, and there is audible clicking coming from the TPS65981ABIRTQR. I’m assuming this means that one of the gates is continuously opening but an issue is occurring, or the power from the source is being rejected. When we apply 5 Volts independent of the USB-C supply to Vbus, there is no clicking but the device is still not operating as expected so I assume that the aforementioned gates is staying open after the initial application of power.

Current changes made:

  • BUSPOWERZ has been connected to GND through 120k resistor (done after issue was noticed)
  • CCn have been connected to their respective RPD_Gn pin to allow boot from no power
  • PP_5V0 and PP_CABLE have been disconnected from GND and connected to 5V0 (no effect on the issue)

I don’t believe the software is causing this issue as the power cycling is occurring quickly and does not reach a high enough voltage to allow the SPI flash to be read from.

Thank you.

  • 0
    Prodigy 40 points

    As an update, I decided to erase the flash memory of the external SPI flash to verify that the issue wasn't caused by the application software, and the issue persisted. I also tried the blank flash behaviour with the TPS65981EVM as a UFP Sink - the power paths PP_HV and PP_5V0 did not put out a voltage so I do not believe it is an issue of them shorting to ground on boot.

    Below are oscilloscope traces of the 5V Vbus input from the USB-C connection as well as the CC line behaviour. It looks like the source tries to power it every ~200 ms with 5V, keeps power for ~30 ms, then drops to 0V again until the next cycle. This behaviour is not present with the EVM as the sink.

    Thank you

  • 0 in reply to Daniel Neasmith
    TI__Mastermind 25616 points

    Hi Daniel,

    Let me see if I can find an expert on the TPS65981 PD controller. Please do note this model is a NRND (not recommended for new design) and only supports PD 2.0, which is no longer certified by USBIF. I'll get back to you next week. 

    Regards,

    Raymond Lin

  • 0 in reply to Daniel Neasmith
    TI__Mastermind 25616 points

    Hi Daniel,

    can you also obtain a PD log? This will help with debugging.

    Thanks and Regards,

    Raymond Lin

  • 0 in reply to Raymond Lin
    Prodigy 40 points

    Hi Raymond,

    I don't believe I will be able to obtain a PD log as the power to the IC is continually reset. Is there a document I can look at which shows how to obtain it?

    Thank you,

    Dan

  • 0 in reply to Daniel Neasmith
    Prodigy 40 points

    As another update, we realized the clicking noise was due to another IC on the board from it booting each time the 5V input reset. So that is not a source of the issue.

  • 0 in reply to Daniel Neasmith
    Prodigy 40 points

    The datasheet of the TPS65981 says to tie PP_HV to GND when unused, and in the application software I have its switch set to 'Disabled', however it seems that in the EVM it continues to output 5 volts (not tied to GND). Even when no flash is used, the PP_HV is high.

    Could this be a source of the issue as our PP_HV is tied to GND? Or is it due to the schematic design of the EVM itself? It is difficult to track in the TPS65981EVM user's guide, at one point it says it connects to SYS_PWR, but there is also a jumper that lets you select if PP_EXT or PP_HV is tied to SYS_PWR (we currently have it tied to PP_EXT).

    Thanks.

  • 0 in reply to Daniel Neasmith
    Prodigy 40 points

    Another update, this is the Vbus and CC behaviour we are seeing. Vbus is channel 1 and CC line is channel 2.

  • 0 in reply to Daniel Neasmith
    TI__Mastermind 25616 points

    Hi Daniel,

    In the Configuration Tool, can you double check and make sure under System Configuration (0x28) PP_HV switch is not used (disabled)? Also in Transmit Source Capabilities (0x32), make sure the switch source is not from Internal High Voltage Power Path (PP_HV).

    Regards,

    Raymond Lin

  • 0 in reply to Raymond Lin
    Prodigy 40 points

    Hi Raymond,

    This is a sink so it does not have any Sourcing capabilities, and yes the PP_HV switch was disabled.

    Either way we believe we found the issue: the VIN_3V3 and VDDIO external PSU should have been supplied power by the TPS65981 through either the PP_HV or PP_EXT paths so that it could control the power input and delay it. We bypassed this by adding a capacitor onto the CE pin of the PSU to delay it instead.

    Thanks for the help,

    Dan