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LM317A: CADJ Capacitor Value

Liang Tsai
Intellectual 2290 points
Part Number: LM317A

Tool/software:

Hi teams,

I was wondering how to determine the value of CADJ. I have scrolled through the datasheet and it only mentioned that the CADJ should be 10uF. Is there any rule while determine the value for CADJ?

Best,

Liang Tsai

  • 0
    TI__Genius 14245 points

    Hi Liang, 

    CADJ is used to improve the PSRR, and reduce the noise on the output. It does this by creating an low pass RC filter with the series resistor R1. with CADJ=10uF and R1=240 Ohm, you get a 3dB cutoff frequency of 66Hz, so if you change CADJ it will change the frequencies that can be filtered. You can recalculate it using the equation below.  

    fc=1/(2*π*CADJ*R1)