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Linear regulator with very low ESR caps

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sefton

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I am using a linear regulator (LM1117). For reasons that I will not go into here, I have to connect 3 caps (470uF each) to the output. The effective ESR of theses caps is less than 0.05Ω. In the data sheet for the LM1117 they recommend an output cap with ESR of 0.3Ω - 22Ω. I remember reading somewhere that if the ESR is too low there can be instability although I don't remember if it was for switchmode or linear. The data sheet specifies a minimum ESR value of 0.3Ω so I am worried about that. Should I connect a series resistance of 0.27Ω ?
Any comments or suggestions will be appreciated.
 

leomecma

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With very low ESR the supply feedback system can oscilate .... the best is use capacitors with more ESR for respect the datasheet ....


leomecma
 

Kral

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sefton,
See National Semiconductors application note AN-1148; the section entitled "ESR and Stability".
Regards,
Kral
 

sefton

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Thanks guys. I checked that app note and it seems that I can't use an LDO here. Unfortunately I am stuck with the low esr cap - cannot change it.
 

huojinsi

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ESR of capacitor is very difficult to estimate. For ur best application,u had better select the recommend capacitor.
 

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