How to combine LDO with buck converter?

Thread Starter


Joined Aug 27, 2021
I want to supply voltage for my IC with 28 V to 5V voltage regulator. IC is noise precise system so I want to try buck converter than LDO.
What are the priorities I should consider?How can I choose voltage regulator?


Joined Feb 24, 2006
You need a set of requirements and a budget.
You have an input voltage and an output voltage. How about some current requirements. How about some requirements for acceptable ripple. How about a description of the types of noise that you want to eliminate or alternatively the type and amount of noise you can tolerate. If you don't consider these things up front there will be no whining about them on the back end of this process. It also makes a difference if this is a one-off design or you intend to manufacture it. For a one-off I suggest that you look for something to purchase. You have essentially zero chance of improving on a commercial product if your requirements are limited to those you outlined in your initial post.


Joined Jun 3, 2019
First buck switcher to bring down the voltage, then rest of the regulation with LDO to reduce the output ripple. Voltage before LDO depends on current output requirement, and LDO dropout voltage. Typically 1-2 volts is ok.


Joined Feb 24, 2006
An LDO with a dropout of 2 volts might be OK if the load current was a couple of hundred mA. That is still less than 1 watt. If the load current is several Amperes then you might not be so happy with that result. The TS really needs to be more specific and thorough in articulating his requirements.