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TPS40200 shuts down

Ryan Parasram
Prodigy 50 points
Other Parts Discussed in Thread: TPS40200

Hi,

I am using the TPS40200 in a flyback configuration and observe the COMP pin railing to 0 for a while before restarting under certain conditions. The COMP pin sticks at zero even though the FB is falling.

ISNS is disabled by shorting pins 7 and 8. And I don't observe VDD falling below 4.1V for a UVLO condition. The soft start pin is connected to ground thru a 1uF X7R ceramic cap in parallel with a 50k resistor, and voltage there looks stable at 3V.

The RC oscillator does not stop during the failure condition. The COMP pin is monitored thru a 100k resistor and the railing to 0 is observed.

What will cause the COMP pin to jump to zero volts? Could the internal 700mV reference be failing? Or could I be missing the soft start observation?

I am assuming that the functional diagram (Fig 4) in the datasheet is close to what is there. Is there another condition that may cause the COMP pin to rail to zero with a falling FB voltage?

  • 0
    TI__Mastermind 24075 points

    Hi Ryan,

    Can you send the schematic in pdf file to my email?

    Q-CHEN@TI.COM

    What's the VDD voltage during failure condition. The typical UVLO turn off threshold is 4.05V, the actual turn off threshold could be higher.

    If the VDD voltage is close to turn off threshold, can you increase VDD voltage to see if the issue goes away?

    Thanks

    Qian

  • 0 in reply to Qian Chen
    Prodigy 50 points
    The part of schematic of interest is sent.

    Note that we have a simple linear pre-regulator that keeps 12V on the switcher.
    Note that the switcher is functioning as a flyback.
    We do not observe VDD falling close to the UVLO shutdown.

    The testing we are doing is in a setup that shorts the input to the pre-regulator for about 1ms with a very high voltage applied to the pre-regulator (500VDC).
    Could exceeding the limits on the FB or COMP pins cause the internal OpAmp to latch up and fail as we observe or the internal reference to fail?