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TPS54225-Q1: Intermittent failure to power on

Ryan Tochtermann87
Prodigy 50 points
Part Number: TPS54225-Q1
Other Parts Discussed in Thread: TPS54225, DS90UB964-Q1,

We have the TPS54225 configured for 5V output based on the TI reference design for this circuit ( http://www.ti.com/tool/ds90ub964-q1evm )

During start-up, when the board has been sitting for an extended period of time, the TPS54225 chip will not turn on as expected. It gets to about 4 volts on the output and then shuts off. Power cycling will resolve the issue and it will not return until either a) extended power down time has passed or b) discharging all capacitors will sometimes get the issue to reappear.

Schematic:

Power on sequence fail

Power on sequence success

Thanks for the help.

  • 0
    TI__Guru**** 191445 points
    TPS54225 can latch off due to OVP or UVP conditions. I will assign this to the reference designer.
  • 0 in reply to JohnTucker
    Prodigy 50 points

    John,

    Thanks for the help with this. Will the reference designer contact me directly?

    We did see an improvement by increasing the soft start capacitance. We don't see the issue with a 47 nF cap but would like to confirm with the reference designer whether any additional testing is needed to ensure the design stability.

    Plot below with a 47 nF cap instead of 3 nF on Soft-start control pin 4.

    Regards,
    Ryan

  • 0 in reply to Ryan Tochtermann87
    TI__Guru**** 191445 points
    Hi Ryan,

    I do not personally know the designer of that reference design. I have sent him an email reminder, but he is OOO until next week. Most likely he is an expert on the DS90UB964-Q1 camera hub, and not real familiar with TPS54225-Q1. Can you tell me about your application? Are you using DS90UB964-Q1? Or do you just have a different application using TPS54225-Q1? Your start up waveform looks normal now.

    You ask about stability. Are you concerned with traditional control loop stability, which is different from start up problems? I notice you are designing with mixed electrolytic and ceramic capacitors. Generally you only need 22 uF to 68 uF all ceramic caps for TPS54225-Q1. I do not believe there are any tools for analyzing stability for TPS54225-Q1. Your only option there would be to manually measure the loop response in your circuit.
  • 0 in reply to JohnTucker
    Prodigy 50 points

    John,

    Our application is using the DS90UB964-Q1, where the TPS54225 is powering the same 1.1V and 3.3V / 1.8V power supplies as the reference design downstream. Thanks for contacting him. At this point we are mostly looking to confirm that this waveform looks normal (which you addressed, thanks) and if there are any other measurements we should make to rule out other possible causes for intermittent start-up. We'll wait on confirmation from the reference designer.

    JohnTucker said:
    You ask about stability. Are you concerned with traditional control loop stability, which is different from start up problems?

    No, I should have been more specific. We currently are not concerned with traditional control loop stability in our application. Thanks for clarifying.

    We appreciate all the help!

    Regards,
    Ryan

  • 0 in reply to Ryan Tochtermann87
    TI__Guru**** 191445 points
    Ryan,

    From the reference design author:
    "I recall the soft start cap value needs to be adjusted. The original design used the values per Fig 13 in the TPS54225 datasheet."

    It looks like you are good to go with your current SS cap value. Let us know if you need further assistance.