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TPS22945 Current-limited load switch not restarting

Stephen Hewitson
Intellectual 305 points
Other Parts Discussed in Thread: TPS22945

Hi,


I've got an intermittent problem that I am trying to track down.

I am using the TPS22945 to protect a CPLD in the event of a latch up condition, but on occasion the TPS22945 will shutdown. I am monitoring the OC pin and it is constantly held low.

I've run some experiments with the over-current protection and the device works as expected - it shuts down for a period of time, then starts again. Similarly, it works as expected with the under-voltage lockout; once the input voltage rises above approx 1.4V the device enables and OC floats.

I believe the issue is caused by switching a load down stream that causes ground-bounce and causes the TPS22945 to enter its under-voltage lockout mode... however on occasion the device never restarts until a full power cycle is forced.

Has anyone seen anything similar, or can offer any advice?

Thanks

  • 0
    TI__Prodigy 130 points

    Hello Stephen,

    Can you send us a schematic with the details of your circuit? We would like to know what CIN, COUT, Rpullup, and load types you may have. I can try to replicated what you have and do some testing in the lab to further investigate the problem.

    Regards, Mark

     

  • 0 in reply to Mark Robinson
    Intellectual 305 points

    Mark,

    Thanks for the reply.

    The product sits at the end of a long ribbon cable that feeds 5V, 15V and some parallel data.

    VIN and ON are shorted together and connected to the 5V from the ribbon cable with a 10u MLCC.

    VOUT is decoupled with a 1u MLCC and directly feeds into an MCP1700-3302E (with 22u, 1u, and 1n on the output). The 3V3 then feeds a CPLD (XCR3128XL), microcontroller (PIC16F636), and MOSFETs for external interfaces.

    I don't have an Rpullup as everything is downstream of the load switch (which doesn't actually switch as its permanently on), and I'd have nothing to monitor it with. For my analysis, I attached a 10k pullup to my 5V supply.

    The output of a CPLD pin goes through a 7400 NOT gate, N-channel MOSFET and is used to switch on a P-channel MOSFET controlling 15V to a small daughter board (1u input capacitor, MIC5201 regulator, 47u output capacitor).

    I added some additional capacitance to the 15V rail, which gave an improvement but didn't eliminate it.

    I have moved the TPS22945 to the other side of the MCP1700-3302E to see if this makes a difference.

    I don't believe I am hitting the current limit, but more likely suffering from the undervoltage lockout not resetting for some reason.

  • 0 in reply to Stephen Hewitson
    TI__Prodigy 130 points

    Stephen,

    I am still invetigateing this, I have not duplicated the problem of a shutdown with no decice restart. Will try some different loading schemes and see what I find. Let me know if you have additional information from your testing.

    Best Regards,

    Mark

     

  • 0 in reply to Mark Robinson
    TI__Expert 5275 points

    Hi,

     

    Has there been any progress here in the last month?

     

    Best Regards,

    Adam Hoover

    Drivers & Load Switch Applications Team

  • 0 in reply to Adam Hoover
    TI__Expert 5275 points

    Hi Stephen,

     

    I will close this out for now, please let us know if you experience any future issues.

     

    Best Regards,

    Adam Hoover

    Drivers and Load Switch Applications Team