Cyclone 4 board - 2 or 4 layers?

[BrianHG]

What do you know about Torex Semiconductor? I'm looking at these two regulators:

https://www.digikey.ca/en/products/detail/torex-semiconductor-ltd/XC6210B252MR-G/2138117
https://www.digikey.ca/en/products/detail/torex-semiconductor-ltd/XC6222B121MR-G/2138183

Their heatsink on their package can only dissipate a puny 250mw.  Do your current and voltage drop calculations to make sure they wont overheat.  Compare that to the the LM1117 you are currently using.

[Miti]

That's 312mA on 2.5V and 119mA on 1.2V from 3.3V. PCB mounted with a bit of copper around, I expect them to dissipate at least 350 - 400 mW.
Anyway, it may be a bit marginal since I don't know how the current is distributed between the voltage rails. Yeah, I know that Intel has a power estimator ...

[BrianHG]

Play it safe....  You are placing this PCB inside another device.  You want clearance for heat coming from that device as well.

Also, the 2.5v should have very little current.  The 1.8v core probably has the higher current.  And, since 1.8v is further from your 5v source, it will generate more heat.

Also, if you look at TI's data sheet for the LM1117, it has copper GND layout recommendations for the GND heatsink pad with which levels of thermal conductivity you will receive.

[langwadt]

Play it safe....  You are placing this PCB inside another device.  You want clearance for heat coming from that device as well.

Also, the 2.5v should have very little current.  The 1.8v core probably has the higher current.  And, since 1.8v is further from your 5v source, it will generate more heat.

Also, if you look at TI's data sheet for the LM1117, it has copper GND layout recommendations for the GND heatsink pad with which levels of thermal conductivity you will receive.

the LM1117 has Vout on the tap and is picky about what output cap you put on it

[Siwastaja]

Consider doing Vcore=1.2V with a switcher from 5V. My secret go-to sauce: SC189CSKTRT and MAMK2520T2R2M + 0603 or 0805 MLCCs, because I don't like generating heat. Not much more expensive or bigger than a linear solution.

Vpll = 2.5V should be very low current and good for linear reg from 5V or from 3V3, but do verify this from the datasheet.

[Miti]

Yes, I think this is the best solution, I was contemplating it. Have you tried that inductor? Looks like the DC resistance is a bit higher than recommended in the IC data sheet.

[Siwastaja]

Yes, I think this is the best solution, I was contemplating it. Have you tried that inductor? Looks like the DC resistance is a bit higher than recommended in the IC data sheet.

Yes but not at full output current but some 500mA so heating is negligible. Of course, do your own loss calculation.