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Design >> Analog Design >> LDO, ESR of the capacitor
https://designers-guide.org/forum/YaBB.pl?num=1177341719

Message started by Faisal on Apr 23^rd, 2007, 8:21am

Title: LDO, ESR of the capacitor
Post by Faisal on Apr 23^rd, 2007, 8:21am

Hi,

I have a questions related to LDO.

ESR variation of capacitor with frequency: What value of the ESR (for the capacitor) should I consider in my simulation? The ESR of the capacitor varies with frequency. At the moment, I take the value of ESR near resonance (from the capacitor data sheet).

Regards,
Faisal

Title: Re: LDO, ESR of the capacitor
Post by zhonghan on Apr 23^rd, 2007, 8:57pm

I think temperature coefficient of ESR is more often concerned . For 1uf ceramic capacitor , typical ESR is 0.01ohm with good immunity to temperature. But for large ceramic capacitor , the variation due to temperatur become prominent.

Title: Re: LDO, ESR of the capacitor
Post by amitsh on Apr 23^rd, 2007, 9:52pm

the typical esr values usually range from 50m ohms to 10 ohms for a standard 4.7uF cap, so depending on the type cap you are using, you should choose appropriate values for esr. for simulation also the esr values make the pole freq change. so chose the value from the cap datasheet and simulate ldo, such that it shouldnt effect your stability of ldo.

Title: Re: LDO, ESR of the capacitor
Post by Faisal on Apr 24^th, 2007, 1:27am

Please see pg 9 of this attached document. ESR vs frequency curves are specified. Now ESR varies considerably with frequency. (Note that these curves are not specified till DC but rather the minimum frequency is 10 Hz)

Which frequency shall I consider for selecting ESR value and why?

Title: Re: LDO, ESR of the capacitor
Post by Faisal on Apr 24^th, 2007, 2:41am

I attach another data-sheet of a ceramic capacitor.

Title: Re: LDO, ESR of the capacitor
Post by Faisal on Apr 26^th, 2007, 1:11am

After modeling the ESR variation vs. frequency as described in the Ken Kundert's paper "Modeling Dielectric Absorption in Capacitors", I have come to conclusion that for LDO, only the ESR value near the resonance frequency is critical.

The Resistance value at low frequencies has no influence either on stability or transient behavior, probably because of high time constants.

I would like to know about the experience of ESR with other LDO designers on this forum