• State Resolved
  • Locked Locked
  • Replies 10 replies
  • Answers 1 answer
  • Subscribers 34 subscribers
  • Views 603 views
  • Users 0 members are here
Support feedback
Options
Options
Related

This thread has been locked.

If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.

TPS65988EVM: RCP Failed with Multi-port Sink, bricked evaluation board

Cory Van Beek
Prodigy 245 points

Part Number: TPS65988EVM

Hello TI Support,

I'm working on a multi-port USB-PD project where our team was testing the TPS65988DH.  Sink RCP is an important design consideration for us, since users could plug in different source devices that negotiate different voltage contracts.  We would also prefer to be able to sink power from multiple sources if they both have the same contracted voltage.

I was testing out the RCP comparator circuit (page 40) on the TPS65988, and it wasn't working properly.  Here is my setup:

  1. Plugged a 5V legacy charger (no PD) into Port A
    1. This powered on the board properly.  I could see in debugging mode with the application customization tool that a cable was connected and the port was in sink mode.  There was no active contract because it was a legacy non-PD charger, but I could see that VBUS was at VBus_5V_Safe.
  2. Plugged a 100 W USB-C charger (I have a Sink RDO for 20 V, 5A) into Port B
    1. I was expecting a result similar to Figure 17 in the TPS65987D, TPS65988 Power Path Performance and Protection Application Note. Once the 20 V RDO was selected, VBUS for Port B would go to 20 V, and bring the SYS_PWR rail up to 20 V with it.  I expected a slight blip on VBUS for port A before the comparator switched on and closed the power switch, but it should stay within 100 mV of 5V
    2. Instead, Port A's voltage went right up with SYS_PWR.  It made it up to about 7V, at which point, it appeared the device reset.  I haven't changed the default settings for OVP (I think the default is 5% of max, but I imagine that OVP settings are like the OCP clamp where the clamp is actually set above the set point). This process repeated about once per second.  After reset, the 5V charger powers the system back on, and the OVP triggers again on Port A after the 20 V RDO is selected on Port B.

Based on that setup, it appears to me that the comparator RCP circuit completely failed. 

I can attach my TPS65988 configuration project if needed.

After that though, the evaluation board isn't working at all.  If I plug in a source device (legacy or PD), the chip doesn't power up.  If I attach 20 V through the barrel jack, it seems the device is continually resetting.  I put the application customization tool in debug mode (attached via micro-USB to FTDI) and it flashes between connected and disconnected.  In the brief moments it connects, I get some weird readings:

  • Mode is "ÿÿÿÿ"
  • Every single Interrupt Event is "True" (even though the interrupt mask is off for everything except cable plug event)
  • The Plug Present field shows a plug even though nothing is plugged in.

Questions:

  1. What might have gone wrong here?  Why would the comparator RCP circuit fail to close the switch?
  2. What might have caused the board to brick out?
  3. Am I better off using power paths 1 and 2 for Sink roles, and use power paths 3 and 4 for Source roles?  Each of our ports has an isolated supply, so RCP seems less important in the sources than the sinks since the sinks are all connected to the same net after the power switch.
  4. I don't think that anything I did should have caused damage to the board.  Is it possible for TI to ship a new one to me?  These things are expensive.

Best regards,

Cory

  • 0
    TI__Mastermind 32691 points

    Cory,

    I am assuming that you are using the both ports of the TPS65988 and connecting the PPHV pins of each port together.

    1.  If you have this case, then you will be (at least briefly) shorting the 2 VBUS ports together through the USB switch. 

    This will potentially cause a large surge of current between the 2 VBUS ports because of the change of voltage.  This may trigger any one of several protection paths in the part.  It should trip the OVP on PPHV and VBUS of the lower voltage port, as well as the RCP of the lower voltage port because of the charge sharing.  It is difficult to determine which protection will be triggered.

    2.  Yes, this type of situation could cause damage to the board because it is going to drive the device in very unintended methods.

    3.  If you wish to do this scheme, then I would put a diode or circuit to isolate PPHV1 and PPHV2 from each other so that the large voltage/current change is blocked by the diode.

    4.  You will have to request a refund from the TI web site.  I am not able to offer refunds.

    Regards,

    Chuck

  • 0 in reply to Chuck Branch
    Prodigy 245 points

    Hello Chuck,

    Thank you for your reply.  I have a couple of follow-up questions.

    1. Relating to answer 1, is the brief short just due to the delay before the comparator switches on and opens the switch?
    2. No Questions
    3. Relating to 3, The motivation behind using the comparator circuit is we wouldn't be losing power across a diode.  If we used the internal power path instead of the external one for our sink path, how would my scenario be different than the example in Figure 17 of the Power Path Performance and Protection application note?  If I need to add a diode to protect my system, it seems like the RCP of the chip doesn't work as advertised.

    Best regards,

    Cory

  • 0 in reply to Cory Van Beek
    TI__Genius 12700 points

    Hi Cory,

    Chuck will be out of office this week and will provide additional feedback once he returns next week.

    Thank you,

    Hari

  • 0 in reply to Hari Patel1
    Prodigy 245 points

    Hi Hari,

    Thank you for letting me know. Happy thanksgiving!

    Best regards,

    Cory

  • 0 in reply to Cory Van Beek
    TI__Mastermind 32691 points

    Cory,

    I am back in the office and working through my holliday backlog.  

    I will reply back tomorrow.

  • 0 in reply to Chuck Branch
    Prodigy 245 points

    Hi Chuck,

    I just wanted to poke this.  I'm finishing up the schematic for our next board spin and I need to know what will work for RCP on the TPS65988.

    Best regards,

    Cory

  • +1 in reply to Cory Van Beek
    TI__Mastermind 32691 points

    Corry,

    I think the issue in your system is the fact that there are 2 RCP circuits and 2 OVP clamps and 2 FET drivers that are all interacting together.  This is likely causing an issue that is outside of what has been simulated.

    We do not recommend using the TPS65988 as a power or circuit for this reason.  This is essentially what you are doing.

    Do you have a MCU in your system?  I have some ideas on how to handle this situation if you do.

    We can configure each port to be a 5V only PDO on first connection, then have the MCU check the state of each port and then query the SOURCE of each port for it's capabilities, then select the optimum power configuration.  

    When 1 port is configured, the other port can be configured to require the MCU to enable to sink path.  This can prevent the issue that you are seeing.

    Doing this is very complicated and will involve a lot of firmware effort, but it will allow you to do what you are trying to do without relying on the RCP in the manner that you are currently doing.

    Regards,

    Chuck

  • 0 in reply to Chuck Branch
    Prodigy 245 points

    Hi Chuck,

    Thank you for the recommendations.  We do have an MCU, but I agree with you that it would be a significant firmware task to handle those commands.  The process makes sense, but it seems that our best bet at this point is probably to just use a Schottky diode and deal with the slight voltage drop.

    Thank you for looking into all of this for me.

    Best regards,

    Cory

  • 0 in reply to Cory Van Beek
    Prodigy 245 points

    One last thing, I got an email on my refund support ticket (CS0792611) saying that I "need to show that engineer from e2e agrees and confirms that device is defective so we can either provide replacement or refund to the customer".  I was wondering if you could comment on that here instead of opening up a whole new ticket.  I still believe that the steps I performed followed the procedure in the Power Path app note.

  • +1 in reply to Cory Van Beek
    TI__Mastermind 32691 points

    Cory,

    Please provide this confirmation to the support team:

    The TPS65988 was not used in a manner that should have damaged the part and this customer should be refunded on this EVM.