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LP5907: Output 1.6MHz 15mV ripple when use a 1uF 0201 cap

Jeff Xie
Intellectual 1780 points
Part Number: LP5907

Hi team,

Customer change 0402 cap to a same value 0201 cap, and find 1.6MHz 15mV ripple. He added a 0.22uF cap in parallel and this ripple disappear. 

Datasheet require output capacitor range is 0.7uF to 10uF, and output capacitor ESR range is 5 to 500mOhm.

1. As impedence and ESR of capacitor is related to frequency, which frequency is specified by datasheet? 

2. As specification is same for these two cap below, what's the cause of ripple?

0201 cap datasheet

https://psearch.cn.murata.com/capacitor/product/GRM155R60J105KE19%23.html

0402 cap datasheet

https://psearch.cn.murata.com/capacitor/product/GRM033R61A105ME15%23.html

  • 0
    TI__Guru 55940 points
    Hi Jeff,

    Please keep in mind that the LP5907 datasheet specifies an output capacitance range for stability of 0.7 to 10 uF. A 1 uF capacitor will not necessarily have 1 uF of capacitance under the application conditions. For more information about capacitor vs capacitance, please refer to Chapter 2 of our LDO Basics E-Book:

    www.ti.com/.../slyy151.pdf

    ESR specifications for LDOs are given at the resonant frequency for the capacitor. This is the lowest point on the capacitor impedance curve.

    Very Respectfully,
    Ryan