Dual power requirement on board

[JohnStein]

Hi All,

I have been lurking around for quite a while and finally decided to take the step and start interacting.  I am new to electronics and have been learning for a while.  I studied basic electronics but that was 20 years ago.  I am fascinated with how things have changed.

I am designing a board that has a two different power requirements.  Some components on the board require 12v and some (MCU) 3.3v.  My input voltage would always be between 12v and 24v.

I have been designing a buck converter circuit for the board and currently my thinking is to use two step down converters (TP5430 (https://datasheet.lcsc.com/lcsc/1811081920_Texas-Instruments-TPS5430DDAR_C9864.pdf)).  The first converter will convert to 12V.  The output from the first converter can then be used on the board for the 12V components and the output also fed into the second TP5430 to convert down to 3.3v.

Is this an efficient design or is there another standard way of achieving this requirement maybe?

Would appreciate any help.

[bob91343]

If you could run the lower voltage from the source it would probably be more efficient, since the load current wouldn't pass through both converters.

[tooki]

I wanna say that I read somewhere that in fact, going through multiple steps is actually more efficient, not less. (I remember because it totally surprised me, as my gut feeling would have been that it’s less efficient.) It might have had to do with the fact that most converters aren’t super efficient at very low load. Doing it in steps keeps each converter loaded a bit more, and I think there were less losses when the voltage drop is smaller.

[tooki]

Hi All,

I have been lurking around for quite a while and finally decided to take the step and start interacting.  I am new to electronics and have been learning for a while.  I studied basic electronics but that was 20 years ago.  I am fascinated with how things have changed.

I am designing a board that has a two different power requirements.  Some components on the board require 12v and some (MCU) 3.3v.  My input voltage would always be between 12v and 24v.

I have been designing a buck converter circuit for the board and currently my thinking is to use two step down converters (TP5430 (https://datasheet.lcsc.com/lcsc/1811081920_Texas-Instruments-TPS5430DDAR_C9864.pdf)).  The first converter will convert to 12V.  The output from the first converter can then be used on the board for the 12V components and the output also fed into the second TP5430 to convert down to 3.3v.

Is this an efficient design or is there another standard way of achieving this requirement maybe?

Would appreciate any help.

Use TI’s Webench power designer tool, on their website, to get reference designs. You put in your parameters (input V, output V, current, minimum component size, etc) and it spits out a list of designs, complete with simulations, schematics, PCB layouts, all of which you can modify and re-simulate. Very useful for working out this kind of thing.

[bdunham7]

How much current will you need on each leg?  That regulator may not work if your V_in drops to anything near your 12 volt output.

[David Hess]

I am designing a board that has a two different power requirements.  Some components on the board require 12v and some (MCU) 3.3v.  My input voltage would always be between 12v and 24v.

The first converter will convert to 12V.  The output from the first converter can then be used on the board for the 12V components and the output also fed into the second TP5430 to convert down to 3.3v.

Is this an efficient design or is there another standard way of achieving this requirement maybe?

There is nothing wrong with that method.  It is what I would do unless I wanted to deal with custom magnetics or had special requirements.