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LM317A: Reproduce "ripple rejection" on EVM?

AnBer
Mastermind 28880 points
Part Number: LM317A
Other Parts Discussed in Thread: LM137, LM317

Team,

Can you please help with the below question?

We are using your Evalution Board LM317A-337N-EVM to test the ripple rejection.
We are interested in reproduce the data of ripple rejection from the datasheet of the LM137 (page 8 Figure 9: ripple rejection vs Voltage output).

The Evaluation Board have an input and output capacitances (C2 & C4 on LM317A-337N-EVM schematic) of 22uF. Could you please confirm us that it is the same input and output capacitors value used during this test? If the value is different, could you provide us the correct ones?

Thanks in advance,

Anthony

  • 0
    TI__Guru 55940 points
    Hi Anthony,

    LM317 was originally released by National Semiconductor over 20 years ago. Unfortunately the exact conditions for Cout were lost in the transition.

    Please note that we do not measure PSRR with an input capacitor. We measure PSRR by using a power amplifier to add a small sine wave on the dc input of the LDO. An input capacitor will reduce the input signal and can cause stability issues with the power amplifier.

    Very Respectfully,
    Ryan