I think this is a common situation so hopefully an answer helps more than just me. I have a 3.3v low power MCU which will be controlling a 5v 5A run of LEDs. When the LEDs are off the system will go to low power sleep mode, however the LEDs have a relatively high quiescent current which I’ll need to cut off. I’ve narrowed my power management setup down to two options with different tradeoffs that I’ve list below but I’d love some feedback on which would be better, if I’m mistaken about something or if I’m missing some other solution.
Everything will be powered from a 9.6v-12v supply.
Option 1) 3.3v rail is its own switching regulator and the 5v rail is also its own dedicated switching regulator rated to above the required 5A. Both lines will be powered directly from the 12v supply and the MCU on the 3.3v line will control the enable pin of the 5V regulator giving it the ability to turn of the 5v line and cut the LED quiescent current.
- Pros - Most efficient on both 5v and 3.3v and I only have to worry about the heat dissipation on the 5v reg.
- Cons - Most complex option with the most components, which means most likely the most expensive and with two switching regulators should I ever need EMC certs it could be tricky. Also at the low loads of sleep mode on the 3.3v rail my switching reg is not at peak efficiency.
Option 2) 5v line is still a 5A rated switching regulator but now the 3.3v line is just an LDO downstream from the 5v rail. The MCU on the 3.3v rail now would not be able to switch off the enable pin on the 5v rail so I would have to use a power mosfet between the 5v regulator and my 5A led strip to kill the quiescent current.
Pros - Simpler design and slightly cheaper replacing the 3.3v switching with the LDO, plus I get back some space on the PCB
Cons - I’ve been researching the power mosfets and I’m worried about heat dissipation if I’m actually driving near 5v 5A. I’m also not sure what having the LDO off the 5v switching regulator will do for my overall power efficiency vs. a 5v and 3.3v dedicate switching reg in option 1, could be this option lets me switch off the quiescent current but then I give that power savings right back by sending power to the micro from a 5v reg to a 3.3v LDO.
As I see it I have a tradeoff between complexity and cost vs. simplicity and possible heat issues. On top of that I have to consider PCB space and possible EMC issues with two switching regulators.
Thanks for any input.