LDO regulator selection

In this post we will be going over some of the base requirements for the selection of a Low Drop Out(LDO) regulator. There are a variety of factors that need to be considered. It seems that a common issues s in making sure that the input voltage has an adequate distance from the output voltage.

The LDO is a good option for a variety of applications where a higher voltage needs to be brought down to a usable level. Due to its simplicity in function and minimal support parts.


The first step in determining what LDO you need is determining what the output voltage will be. There is a wide range for the output options available.
Voltage output

Now that you have determined your output voltage you can select the current that you are looking for in your output. Since devices will only pull the amount of current that they need having a LDO that can output a bit more current than needed can possibly extend the service life of the LDO. If you underrate the current output that you need the device could shut down and go into a self-preservation mode until the load is removed or another qualifying situation.

Current output

One thing to consider when selecting a LDO is to be certain that the input voltage is above the output voltage per the datasheet following the specification for the drop out voltage. There is quite a range of drop out voltage depending on the part being used. Digi-Key carries options from .1V all the way up to 15V. With a majority of these in the sub 3V range.

Voltage dropout

Here is a formula for calculating what is needed to make sure the input is the appropriate distance from the output.


The quiescent current for the LDO is the amount of draw that will be put on the source when there is no load on the LDO. Higher the current the faster a battery would drain if the LDO is being used in a battery application.

Even though that are a variety of other factors to be considered when selecting an LDO these are a good starting point to get you going in the right direction.

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