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LM4132: capacitor inquiry

Cedrick
Expert 8270 points
Part Number: LM4132

Hi,

Good day. I hope you are doing well.

Our customer has this inquiry about the LM4132. Can you please help us? Thank you.

We have implemented the LM4132DMF-3V3 in a new design. The part supplies 3.3V rail to a TCXO. We have measured too much noise transferred from the LDO to the TCXO. We also tested that using 44uF capacitor at the input and output of the LDO the noise effect is reduced. Now , the datasheet does not say if 44uF at the output can make the LDO unstable. what is your advise?

The datasheet is not clear. It advises that the LDO is stable with Cout=10uF. It does not say if this is by design or by measurements. It also states that it is possible to use Cin>=Cout and Cin up to 22uF.

My question is if I can use 44uF=Cout=Cin without having stability issues with the LDO.

Looking forward to your help. Thank you.

Regards,

Cedrick



  • 0
    TI__Intellectual 1735 points

    Hi Cedrick,

    To clarify, this is a voltage reference - is it being used as a power regulator? If so, it may be improperly suited to the task since voltage references generally trade off output current capability for better noise and stability performance.

    Given this, you can still use it as an LDO if you are careful with not loading the part too much.

    To answer your question - yes, you can probably put capacitors that large on the input and output - just recognize that startup times will be affected due to large capacitance.

    If you run into stability issues, there is also the option of adding a small series resistance (1ohm) after the vref output and before Cout.

    Let me know if this addresses your question.

    -Tony