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How to choose the best LDO for your projects?

by: Apr 19,2021 2131 Views 0 Comments Posted in PCB Design Tutorial

PCB Design Tutorial Circuit PCB layout LDO

Summary:       One of the most used components in electronic circuits is definitely the Low-dropout regulator (LDO). And I will explain how to choose the most suitable LDO for your project. And I will also show you which are the most important parameters of an LDO.


LDOs are used in different types of devices because they play a fundamental role within a circuit. Because they supply specific voltages to microcontrollers, microprocessors, sensors, drivers, etc. Choosing the most suitable LDO is not easy, because several parameters must be carefully evaluated. We must pay close attention to the efficiency of an LDO when our circuit is battery-powered. So, if we choose an LDO with excellent efficiency, we will be able to power our circuit for a longer period. Otherwise, our circuit will not be efficient so we will have to charge the battery more often.

When to use an LDO?

Most microcontrollers/sensors and other similar components have a working voltage of 3V3. If we decide to power our circuit with a voltage higher than 3V3 then we will have to find a way to reduce them. For example, if we power our circuit through a USB connector then we would most likely have an input voltage of 5V.

How to solve the problem

To solve this problem we need to choose an appropriate LDO for our circuit. In some cases, multiple LDOs can be used to get different voltage values that we need to make our circuit work. Obviously, we must keep in mind that each LDO has its own voltage drop caused by the internal components.

Can a voltage divider be used to regulate the voltage?

No, a voltage divider cannot be used as a regulator. A voltage divider is generally used to scale a voltage so that it can be sensed/detected/analyzed more easily. For example, if you want to detect the charge level of a battery.

LDOs are used to regulate the voltage of our circuit because they guarantee a constant output voltage, even if there is a variation in the input (which respects the operating limits of the component). A voltage divider cannot do this.

The important parameters to evaluate when choosing the LDO

A very common mistake is to choose an LDO with parameters that are not suitable for the type of use. For example, a lot of users using AMS1117 for all kinds of projects - this is wrong because you need a power-efficient solution, the AMS1117 is not suitable. Below you will find a screenshot with the main features of the AMS1117.

Here are the features of another AP2112K LDO. Below you will find a screenshot with the main features.

Here are some of the most important parameters:

LDO Efficiency

Here's how to calculate the efficiency of an LDO:

Input voltage

The input voltage range determines the maximum and minimum allowable voltage value for LDO. The input voltage must be higher than the LDO output voltage plus the drop voltage. Furthermore, if the input voltage exceeds the maximum allowed value, the LDO risks being damaged.

Dropout Voltage Parameter

The dropout voltage is the differential voltage between the input and the output for which the regulator output. The LDO must supply constant voltage when for example the battery runs out. Now a small dropout voltage is very important because the lower the dropout voltage, the higher the input voltage, and therefore the longer the operating time.

Output voltage

This value depends on what you need to power, sensors, microcontrollers, etc.

LDO with manual adjust

There are some LDOs that allow the regulation of the output voltage through a voltage divider. These types of LDOs are very useful when we need a specific voltage value.

Output Current

If you only need to power a sensor or component that consumes little energy, do not choose an LDO with a maximum output current of 1A, choose an LDO with a maximum output current of for example 150 / 300mA. Sizing the components of your circuits well allows you to have an efficient, compact, and economical circuit.

Quiescent Current

Is the current required to power the LDO's internal circuitry when the external load current is zero. If your circuit must be efficient in terms of consumption because for example it is powered by a battery, the Iq becomes a very important parameter. It includes the operating currents of the band-gap reference, error amplifier, overcurrent, and overtemperature sensing circuits.

Noise output voltage parameter

Most of the noise comes from flickering noise in the internal LDO voltage reference. In fact, this parameter is the RMS output noise voltage generated only by the LDO over a frequency range.


Linear Low Dropout (LDO) is a key component used in multiple applications. So in the future when designing a new circuit where it will be necessary to use an LDO, read the documentation carefully and look for the perfect component for the circuit you need to build. And now you know how to choose the most suitable LDO for your circuit. I hope this post was useful for you to develop your PCBs. If you have any questions, don't hesitate to ask.

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