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TL751M05QKVURQ1

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Replies: 6

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The TL751M05QKVURQ1 chip is selected when the output MLCC is not 10uf, the ripple is still 400mv, and the output MLCC is replaced by 33uf and the ripple is 200mv. This is obviously different from the claimed data of 150mv. I suspect this chip is It’s not a problem with itself, or it’s impossible to ripple so much.

  • Hi Meng,

    Can you share the ESR of the capacitor or part number? The datasheet pages 6 and 7 describe the output capacitor requirements for stability. A ceramic capacitor (MLCC) will not have enough ESR for this linear regulator. You will need to add a series resistor with the capacitor for stability.

    Best,
    Eric Preiss | Validation Manager | Linear and Low Dropout Regulators | Texas Instruments

  • In reply to Eric.Preiss:

    Hi Meng,

    It sounds like the TL751M05 is oscillating with your MLCC output capacitors. When the linear regulator is stable, you should not see measurable ripple on the output with an oscilloscope unless you have very large ripple on the regulator input.

    PSRR typical is 55 dB.
    PSRR (dB) = 20 x log(Vin/Vout)

    Vout = Vin/(10^(PSRR/20))
    If the input ripple was 1 V peak-peak, then the output ripple would be 1.8 mV peak-peak (typical).

    Best,
    Eric Preiss | Validation Manager | Linear and Low Dropout Regulators | Texas Instruments

  • In reply to Eric.Preiss:

    If external compensation, is it on the capacitor loop?
  • In reply to Meng jeffrey:

    Hi Meng,

    The output capacitor is part of the feedback loop and must be selected according to datasheet recommendations for the regulator to be stable. This is a PNP regulator and you can read more about how the output capacitor affects stability in this application note:
    www.ti.com/.../snoa826.pdf

    Best,
    Eric Preiss | Validation Manager | Linear and Low Dropout Regulators | Texas Instruments

  • In reply to Eric.Preiss:

    See pages 8-11 of that linked application note for section: LDO Regulator Compensation.
    The ESR of the output capacitor introduces a zero to the feedback loop gain, allowing the regulator to be stable. The ESR can be implemented with an external resistor in series with the output capacitor or it can be internal ESR of the capacitor.

    Best,
    Eric Preiss | Validation Manager | Linear and Low Dropout Regulators | Texas Instruments

  • In reply to Eric.Preiss:

    Hi Meng,

    I haven’t heard back from you. I’m assuming you were able to resolve your issue. If not, just post a reply below or create a new thread if the thread has locked due to time-out.

    Best,
    Eric Preiss | Validation Manager | Linear and Low Dropout Regulators | Texas Instruments

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