FEDEVEL
Platform forum

Shar , 04-02-2025, 12:10 PM

I need to design power section schematic for our board. The main SoC has two rails of 1.2v (core)with absolute maximum current rating of 95mAand other 3.3v with absolute maximum power supply rating of 20mA . And a third rail of 4v is required for network card section which is rated for max 2Amp. Input will be 9v.
How should I proceed with the design....for 9v to 4v I will use a switching regulator.
But for 9v to 3.3v and 1.2 v should I use switching regulator or LDO.(since current is very less in mA)......
Or use a switching regulator for 9 to 3.3 v and then ldo for 3.3v to 1.2v........
And then while choosing these ics cost is our main concern...
Inputs required @Robert Feranec

QDrives , 04-02-2025, 02:56 PM

Switching is always more expensive. Both regulator and 'supporting' components.
On the other hand there is power efficiency. This especially important for battery powered applications.
Do note that 2x95mA from 4V to 1.2V is a 0.53W loss when using LDO. But that is "maximum" as you mentioned.

Elsayed Rakha || Egypt , 04-03-2025, 10:29 AM

*Use a Switching Regulator to convert 9V to 3.3V, then use an LDO to convert 3.3V to 1.2V.*

This can improve efficiency slightly, but since the current is very low, the benefit may not be worth the extra cost and complexity.


//**Cost Optimization**//
Use LDOs for low-current rails (1.2V & 3.3V) to save cost.

Only use a Switching Regulator for the high-current 4V rail.

Shar , 04-06-2025, 06:08 AM

Ok thank you

Robert Feranec , 04-07-2025, 06:04 AM

I would probably do it like: 4V switching from 9V (looks like this may be noisy ?). 3V3 switching from 9V, 1.2 linear from 3V.

Shar , 04-08-2025, 05:15 AM

What if I use switching regulator for 9v to 4v and then step down 4v to 3.3v and 1.2 v using two LDOs?

Robert Feranec , 04-08-2025, 11:52 AM

I don't know what kind of module you are going to connect to 4V but with 2A peak it looks to me like a GSM module or some other kind of module which can make power very noisy. that is why I suggested to split it at 9V

QDrives , 04-08-2025, 03:44 PM

That will still 'port' the noise to the 9V.
Do the 1.2V sections need to be separate? Or can this be a single 1.2V?

Shar , 04-09-2025, 08:23 AM

Yes it's a LTE wireless module