LM2940 regulator question!

Discussion in 'General Electronics Chat' started by bobsuper, Mar 14, 2011.

  1. bobsuper

    Thread Starter New Member

    Mar 14, 2011
    I want to regulate the 14.8 volts from a LiPo battery pack to 12 volts using a lm2940 low-dropout regulator. I have read the datasheet and understand I need an output capacitor with an low-ESR in the specified range, minimum 22 uf, to prevent the regulator from oscillating.

    However, in the datasheet the specified ESR is from ~0.1 to 1 @ 100kHz, so I am a bit confused at to what capacitor type to use for my application.
    And I am dealing with DC voltage from the battery, so why is frequency mentionned? I thought frequency had to do with AC...

    After some research, I settled for a 100 uf tantalum capacitor, datasheet is http://www.avx.com/docs/Catalogs/tap.pdf (scroll down to "16v@85 degrees"), because the ESR is said to be 0.8 ohms @ 100kHz.
    Does that work? The ESR on the cap's datasheet is given for the same frequency as on the lm2940 datasheet, so I guess it's a match...

    It's not mentionned that the input cap has to be low-esr so I guess a normal type will work...

    So if someone can help...

    Thanks a lot!