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Design >> Analog Design >> LDO compensation schemes comparison
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Message started by hchanda on Oct 17^th, 2007, 5:28pm

Title: LDO compensation schemes comparison
Post by hchanda on Oct 17^th, 2007, 5:28pm

Hi all,

Attaching a pdf which shows two kinds of compensation schemes for LDO.

The first slide inserts Rc and Cc for frequency compensation between the output of error amplifier and VOUT (output of regulator)
This way it spilts the poles seen at the output of error amp. and at the output of LDO.

The second slide inserts Cc for frequency compensation across resistor R1. Can you please explain how it will help in compensating the loop?

Also what are the advantages/disavantages of one method over the other?

Thanks
hc

Title: Re: LDO compensation schemes comparison
Post by hchanda on Oct 17^th, 2007, 5:54pm

sorry I have drawn them wrong earlier. Attaching the corrected one.

Title: Re: LDO compensation schemes comparison
Post by buddypoor on Oct 23^rd, 2007, 5:58am

The second scheme (C across both resistors) is the preferred one, however it is important either to choose a capacitor with a rather big LSR (leakage series resistor) or - to be on the safe side - to put an extra resistor of about 5 to 10 ohms in series to the capacitor.
By doing this and in order to stabilize the circuit the loop gain is a) reduced and b) its frequency response will cross the 0-db_line with a slope of about 20 dB/Dec.
(This can be easily proved in the BODE-Diagram)
Any further question ?
Regards
Lutz