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LM27761: Maximum output capacitance

Marcel Schildknecht
Prodigy 90 points
Part Number: LM27761
Other Parts Discussed in Thread: LP5907

What is the maximum capacitance that can be connected to the LDO output for stability, or can it be increased without limit? I would connect around 100uF.

Output current ~10mA. The other three capacitors would be according the example in the datasheet. LDO output voltage -2.5V.

  • 0
    TI__Mastermind 23840 points

    Hi Marcel,

    LM27761 requires the use of only a 2.2-µF ceramic output capacitor for stable operation. Of course you may increase the output capacitance slightly. But 100uF seems much higher than the recommended value and there will be stability issues with such a high output capacitance. I recommend to choose a value in the range of the recommended value.

    Please let me know if I can help you further.

    Regards,

    Febin

  • 0 in reply to Febin
    Prodigy 90 points

    What means "slightly increase"? Is there a design limit?

    For example, the LP5907 states a maximum capacitance of 10uF in the datasheet. I'm looking for a similar specs for the LM27761.

  • 0 in reply to Marcel Schildknecht
    TI__Mastermind 23840 points

    Hi Marcel,

    I totally understand your concern.

    LM27761 is a very old device. Yes, the datasheet does not specify the limits. Unfortunately, I will not be able to provide any maximum value for the output capacitance as it would be like extending the datasheet. I would suggest to keep it below 10uF and test for stability.

    In any case, the customer needs to perform bode plot measurements if the BOM is outside the typical recommendations in the datasheet. Another suggestion would be to do transient simulations for the desired BOM and then test it on the bench.

    I hope this helps.

    Regards,

    Febin

  • 0 in reply to Febin
    TI__Mastermind 23840 points

    Hi Marcel,

    I would like to close this thread, if you don't have any further questions.

    Regards,

    Febin

  • 0 in reply to Febin
    Prodigy 90 points

    You can close the thread

  • 0 in reply to Marcel Schildknecht
    TI__Mastermind 23840 points

    Hi Marcel,

    Thank you for the confirmation.

    Regards,

    Febin