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Original question:

LM117HVQML:LM117HVQML

LM117HVQML:LM117HVQML

HIROKAZU MONMA
Prodigy 40 points
Part Number: LM117HVQML

Tool/software:

Please advise on ① and ② below.

① Regarding the ripple rejection rate, the "Ripple Rejection" chart shows that it is 10dB at 1MHz (max), but what happens when it is between 1MHz and 400MHz?

Will it no longer be able to respond to high frequencies and rise above 10dB?

② If a 100Ω and 6000μF RC filter is installed on the output side, the response on the output side will be slower, so I think the ripple rejection rate will also improve. What do you think?

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    TI__Mastermind 45635 points

    Hi,

    The LDO bandwidth is around 100kHz ~ 200kHz at full load (bandwidth increases with increasing load), so frequencies outside of this range are not reduced by the device loop but are reduced by the output capacitor. But, up to 400MHz even the output capacitor is inductive and PSRR won't be good. For these reasons, a filter at the output is a good idea. I'm no expert on filter design, but I imagine that using a simple RC filter (even with a very large C) will have the same issues since the cap will still be inductive at 400MHz. 

    Regards,

    Nick