How to determine the error amplifier’s gain and unit gain frequency for a LDO design?

[chungming]

How to determine the error amplifier’s gain and unit gain frequency for a LDO design?

Hi~~
This is my first time to design a LDO.
I have seen some theses about it.
But i have some questions about that:
How to determine the error amplifier’s gain & unit gain frequency? How much it is?
And how larger size the pass element has?
Is the length of pass element can use minimum size (ex in .35um process, length using 0.35um)?

Thanks a lot ~!!!!!!!!

 

[ambreesh]

Re: LDO design questions

Download the PhD thesis of Rinconmora from the following link.
that would answer all your questions
**broken link removed**

 

[safwatonline]

LDO design questions

error amp. gain will set ur DC regulation, GBW will set the high freq. rejection.

size of Mpass depends on ur dropOut voltage , and if u can afford that u let it enter triode

usually it is min. size to get min. overdrive without increasing the width very much

 

[chungming]

Re: LDO design questions

safwatonline, ambreesh :
thanks a lot ~~!!!

 

[rfzheng]

LDO design questions

that is depende on your spec.

normally mini channel length is best choice for your power MOSFET

opamp dc gain consider in the loop of the LDO .
loop compenation and loop gain, loop unit frequency should be considered in all.

so it is nor easily to say what is the best.

 

[yen]

Re: LDO design questions

Hello,
I have two questions.
1.I want to design LDO. I have a question.
How much of my power mos's size?
It's size is larger, load current is larger.
But it may be have a big capacitor.
So how do I do?
2.I am studying Switching regulator.
I don't understand PWM and PFM.
I want to know which circuits do a Switching regulator consist of.
Like PWM,PFM, over current detection....?
If you know,please tell me.Thanks.

 

[krishnareddy]

LDO design questions

loop dynamics of the ldo determines loopbandwidth and phase margin. steady state accuract determines loop gain. maximum load current and drop out voltage determines pass transistor size. erroe amplifier gain is part of loop gain. error amplifiers bandwidth is decided by the choice of its pole which is governed by loop stability constraints