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Design >> Analog Design >> LDO design
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Message started by spanandiyer1979 on Oct 29^th, 2008, 11:45am

Title: LDO design
Post by spanandiyer1979 on Oct 29^th, 2008, 11:45am

hi

i have to design a low drop out regulator with an input voltage range of 2.8+/-10% , output voltage of 1.8V and a load current of 10mA to 50mA.I am new to LDO design. Can anybody let me know the design methodology for this ldo. i mean from the system specs , down to the amplifier specs etc. any pointers would be helpful.

thanks
anand

Title: Re: LDO design
Post by buddypoor on Oct 29^th, 2008, 12:35pm

Hi spanandiyer1979,

I don´t know your technical/theoretical background - therefore, please excuse me if I tell you something what you already know.
Searching in the internet you certainly will find a lot of papers, contributions and documents about LDO´s.
However, my recommendation is, before starting with LDO design to become familiar with the basics of control theory.

A LDO is a system with feedback, which is designed based on certain rules derived from control theory. At least you should know what the following terms mean (hopefully I didn´t forget something):

Positive/negative feedback, stability, loop gain, stability/phase margin,
Bode and Nyquist diagrams, pole/zero distribution and their relationship to the dynamic properties of a system,....

Regards and good luck.
Buddypoor

Title: Re: LDO design
Post by spanandiyer1979 on Oct 30^th, 2008, 11:28am

Hi Buddypoor

I have a good background on electrical engineering and I am used to designing PLLs. So I am familiar with the things you mentioned. I was looking at obtaining a design methodology for a fully integrated LDO(meaning no external capacitance at the output) with the specifications mentioned.

Please let me know if you could direct me to specific papers etc since the discrete designs available in ti.com use external capacitors.

Thanks
Anand

Title: Re: LDO design
Post by buddypoor on Oct 30^th, 2008, 12:35pm

Hello,

I´m not sure if the following document link contains some interesting information for you; it´s a 109 page description of an LDO design process.

http://www.micrel.com/_PDF/other/LDOBk.pdf

Regards
LvW

Title: Re: LDO design
Post by ywguo on Nov 4^th, 2008, 12:30am

I think Dr. Rincon-Mora's thesis is a good source.
http://users.ece.gatech.edu/rincon-mora/publicat/books/thesis/

Yawei

Title: Re: LDO design
Post by Dan Clement on Jan 25^th, 2009, 10:59pm

LDO regulators can be very tough to design. The biggest issue is usually that you need to be stable for a huge range of loads while not consuming much power in your error amp.

You also have to take care of reliability with good layout for latchup and ESD immunity.