Selecting a linear regulator to provide clean VDD

Hi, all.

I am trying to set up for testing IC. I have to give VDD for both digital and analog using voltage regulators. For example, if I have two regulators - one for digital VDD and the other for analog VDD.

One big simple question is...If I want to provide clean as possible VDD with good isolation between digital and analog sides, should I need to use voltage regulators? Is this good idea?

I am thinking of buying linear regulators from linear technology. Under power management menu on the left of the website (https://www.linear.com/), I see many regulators. I picked linear regulators.
Particulary, postivie regulator.

Say, I chose (LT1121-3.3) - my chip works at 3.3V for both analog and digital.
https://www.linear.com/pc/downloadDocument.do?navId=H0,C1,C1003,C1040,C1055,P1368,D2188

It says, under features, adjustable output from 3.75V to 30V. In addition, it also says 3.3V and 5V fixed output voltages. What's the difference between two features under the same chip.

Should I buy a low drop out voltage one as well? Why LDO is important in general?

Any help is welcom.

Thanks,
BJ

Re: Linear regulator

Hi ee484,

yes I would use the linear regulator. The will be clean and if you are just testing then you probably are not in great need of high efficiency like a switcher will give. The LDO is mainly used when you want to get as much out of the raw voltage as possible so instead of going unregulated when the input voltage drops to within 3 volts of the output the LDO will go out of regulation at a much lower differential. Your linear regulators come in either fixed voltage outputs or adjustable with voltage dividers for feedback.

hope that helps

Regards

dfullmer