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OPA4172: output voltage is locked to low status

Part Number: OPA4172

Hi Team,

Customer is consulting below amplifier's output voltage is locked to -3.8V until resetting power supply. The OPA4172 is powered by ±5V, and the input voltage of pin 2/3 is basically 0V, but pin 1 outputs is locked to be -3.8V. And it does not recover to normal until it is powered off and on. Do u know what's the root cause here? Thanks.

Best,

Stanley.

  • Hi Stanley,

    what signals are coming from the left? And what everything is connected to the output of OPAmp?

    Did you notice that the OPA4172 is no input rail-to-rail OPAmp and that the input voltage should not rise above +5V - 2V = +3V?

    Kai

  • Hi Kai,

    Update total Schematic below. The current transducer(U501A)'s ratio is 1:2000. Below circuit is for current sample. The InvRCurr+/InvRCurr- will be in ±1.375V. When circuit is abnormal, the value for InvRCurr+/InvRCurr- will be larger. 

    The key concern for customer is our device will be locked to -3.8V, which never recovery to normal until resetting power supply.

    Best,

    Stanley

  • Hello Stanley,

    When the output is stuck at -3.8V, what are the voltages at pins 2, 3, 4, 11 at this time?

  • Hi Stanley,

    hmm, looks fine so far. Could be a power supply sequencing issue: If the current sensor is already powered while the OPA4172 is not, latch-up could occur. The add of a diode clamp could help.

    Or the current sensor is overdriving the OPA4172 during normal operation. The change of input voltage divider could be a remedy, so that even with maximum output voltage of current sensor the common mode input voltage range of OPA4172 isn't violated.

    As being a bit paranoid, I would combine both measures Relaxed

    By the way, C617 is a bit small for my taste. Why not increasing it up to 100nF or so? It would help to filter out unwanted glitches, if this is what causes the latch-up.

    Kai

  • Here the datasheet of your current sensor:

    4646-X201_en-277115-1.pdf

    Kai

  • Hi Kai,

    Many thanks for your very detailed explanations. It does help. You mentioned adding a diode clamp could help supply sequencing issue. Can you demonstrate how to add it? Thanks again. 

    Best,

    Stanley