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What are the most important parameters of an opamp used in LDO

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anhtuan

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Hi!
I'm intend to design a LDO as the picture below. So i'm finding documents about it, if anyone have documents please send to me! Thanks
 

Re: LDO design

Hi ,
Your project seems great, Can you explain for me the function of each block so we can discuss about your project ?
Thanks.
 

Re: LDO design

it's available Chip in market. So,I just try to design it but i don't have Schematic and documents about it!

Another question: What the most important parameters of the Opamp used in LDO (BW, Av, SR,noise..)??
 

Re: LDO design

I think the most important parameters for an opamp in a LDO are PSRR and offset voltage, since they would directly affect your output accuracy. Open loop gain is also important to have better accuracy. Slew Rate and noise are important according as the specification of your LDO and the reference level.
 

Re: LDO design

what kind of components used in LDO design? BJT,CMOS, or DMOS...??and Why??
 

Re: LDO design

All of them may be used. Reasons depend on your specifications. DMOS if you need high voltage operation. BJT if you need good accuracy and low offset Opamps. MOS otherwise.
 

LDO design

your design maybe large.
 

Re: LDO design

can you tell some specifications about it?
 

Re: LDO design

what is DMOS? Is there any differences between DMOS and CMOS?
Thanks.
 

Re: LDO design

I have just design a LDO same as your figure . But If I upload it , My boss
will .....
So what I may say is , the main constraint on the design is the PSRR of
voltage reference , and the eror amplifier is 1 stage with a buffer ..
nothing is special !
 

Re: LDO design

:)
Now i am designing a same LDO as yours.
But i have a question about LDO.
How to compesation frequence of the LDO?
Who have this kind of experience?
 

Re: LDO design

I think all of us are the new beginer. if anybody have documents about LDO please upload for us. So,we can discuss...

Added after 1 hours 27 minutes:

to :fanrong
Why you just use the 1st stage opamp. The opamp in LDO has gain usualy more than 60dB???
 

Re: LDO design

horzonbluz said:
:)
Now i am designing a same LDO as yours.
But i have a question about LDO.
How to compesation frequence of the LDO?
Who have this kind of experience?

There are many ways you may use for compensation for example:
1. Dominant Pole Compensation
2. Gain Compensation
3. Lead Compensation
4. Lag-Lead Compensation
 

Re: LDO design

Gabriel Rincon-Mora - "Current Efficient, Low Voltage, Low Drop-Out Regulators"

hxxp://users.ece.gatech.edu/rincon-mora/publicat/books/thesis/ldo_book.pdf

On hxxp://users.ece.gatech.edu/rincon-mora/publicat/ there are many useful papers for designing LDO
 

Re: LDO design

It's so pity that i cannot login in.
But the ldo book is very useful.
 

Re: LDO design

To anhtuan,

I think you had better confirm spec. and target of the LDO at first, as to achieve different targets you should apply quite different schematics.

To horzonbluz,

If you want to know how to compensate the frequency, this article may be helpful.



Saimen
 

LDO design

DMOS is high voltage CMOS device , it is different with LDD structure cmos device ..

by the way , CMOS LDO , you can use OPA + nmos or pmos

nmos response is fast , but use for small output (nmos have Vth drop )
 

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