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TPS23861 Semi-Auto mode drop out before power enable

Jeff Witrock
Prodigy 30 points
Other Parts Discussed in Thread: TPS23861

I am encountering a problem using the TPS23861 in semi-auto mode.

In auto mode everything works fine.  When I plug a PD into a port, I see detection, classification, and power up fine for class (0-4).  Two event classification is also working.

In semi-auto mode, I have detect and classification enabled (register 0x14 set to 0xFF,  DETE and CLE bits set for all ports)

When a PD is connected, I can see detection and classification occurring properly.

When I set the power enable push button register PWONx bit to 1, power to the port is enabled,.

The problem is that there is approximately a 1ms period after the classification and before power is enabled where the voltage drops below the MARK level.  This is causing a problem for some PD especially class 4.  Class 4 devices are not seeing our device as a class 2 PSE probably because the drop below mark level is causing the PD to reset and so it will not see the second classification event.

I do not have an oscilloscope screen shot right now, but below shows what I am seeing.  The trace marked in red is what I see in semi-auto mode.  In auto mode, I do not see this drop out.

The data sheet section 7.4.3 explains that in semi auto mode, a new detection/classification will occur after the PWON bit is set if needed to meet the 400ms detection to power on time limit, but it looks like there is some period after classification and before power on where the output is not being driven.

Any help is appreciated.

  • 0
    TI__Genius 15655 points

    Hi Jeff,

    What kind of PD did you use when you saw this issue? Did you use an external MCU to control TPS23861?  If yes, please check our MSP430 reference code to turn on the port properly. If you want to get better understanding of the code, please email me at p-xu@ti.com . Thanks.

    Best regards,

    Penny

  • 0 in reply to Penny Xu
    Prodigy 30 points
    Hello Penny,

    I have been using a number of different cameras and also as a test I have been able to reproduce the problem using just a PDJack with a light maintaining load.
    www.molex.com/.../datasheet.jsp

    I see the "droop" regardless of the PD I use. So far, it is causing us problems with class 4 devices because of the missed two-event classification.

    We are using a microcontroller to control the TPS23861. When I originally wrote the firmware, I used the reference code you mentioned as a starting point.

    After seeing this problem, I have also cut the code down to the bare essential of putting the part into semi-auto mode with detect/classification enabled, and using the PWON to enable and I am seeing the same problem.

    Thanks,
  • 0 in reply to Jeff Witrock
    Prodigy 30 points

    OK, I want back to download the most recent reference design, and now I see that instead of using the PWON command, the reference design

    1.  switches the port to auto mode to enable power

    2.  once power up is finished, it switches the port back to semi-auto

    Is this to work around the issue I am seeing?

    Thanks,

  • 0 in reply to Jeff Witrock
    TI__Genius 15655 points

    Hi Jeff,

    Yes. You got it right. We have new devices available for sampling now so that you don't need to implement this workaround. Please contact me through email and we can figure out how to send you the samples if you want. Thanks.

    Best regards,

    Penny