Tuesday 20 January 2015

power supply - 1.2V, 2.5V and 3.3V from 5V


I have a slightly ambitious project for my first PCB: I want to control a wall of WS2812 LEDs from an Altera CycloneIV. The LEDs are connected to a rail carrying the 5V supply, at up to 350W, and expect their control signals at 5V as well.


For the FPGA, I need 1.2V (core), 2.5V (PLL) and 3.3V (I/O).


I'm routing the I/Os (40 of them) to voltage converters to bring them up to 5V and get ESD protection.


My current approach would be a linear regulator for 3.3V, as I expect the current draw to be minimal, and there isn't much room to work with; for 2.5V and 1.2V I'd use a switching converter each and add large capacitors for stability.


For additional safety I could place reverse-facing diodes between the five voltage levels, although I'm not sure these are actually required.


Is that a viable approach, or can this be improved somehow?




Answer



You can generate all three rails (3.3, 2.5 and 1.2) from a single chip, the Alegro A4490: Triple Output Step-Down Switching Regulator. It is available from Digi-Key in a 20-VQFN package.


I have used this chip in several projects, and it works fine. You can run at least 2A through each output.


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