Well, I was calculating absolute maximums, not necessarily the average current the regs would be putting out.
In my particular setup for example, I would like to power a 3v vibration motor or a few lasers. A massive 10G vibration motor or a green laser might need 200mA. A smaller vibration motor or three red lasers might need 150mA. And a small vibration motor or a single laser might need onl 60mA. But in any case, they would only be on for brief periods of time. A few seconds at most, usually.
One thing about those teensy-weensy v.regs is they might work ok in a dedicated app, like a cellphone/whatever where
you know what the load will always be, but when you have a more general-purpose board, you never know what might
be connected to it.
Just think, 150degC = ~300degF. That's almost the temperature most things are cooked at in the oven. If nothing else,
you run the possible risk of someone burning the heck out of their fingers. To me, even the 175degF I mentioned is
more than I want to reckon with.
The switch on/off bit is a problem, but I still might look for a more robust part with enable.
Well, my plan as of this moment is to forget trying to run the 3.3v off the battery because even a NiMh doesn't leave me with much amperage to work with before the 3.3v reg would overheat. So the plan now is to run both 3.3v regs on my board off the 5v regulator. That will allow them to put put almost 350mA, which is 150mA more than what I ever expect the reg will need to put out, and even if does get to 200mA, it will only be for brief periods as I mentioned earlier.
Even running off 5V is a problem. (5V-3.3V) * 0.2A = 0.34W * 206degC/W = 75degC temp rise. That still gives 212degF
on the part. For me, that's too hot, boiling water hot, but it's your board.
... but I don't really have the space for it, and it would make the way everything connects to the main board a lot more complicated for people. Trying to keep things simple. The board is already studded with pinouts:
Space is always a problem on pcbs. I can never get them as small as the original goal. Having burned up boards is
worse. In the end, you just have to make your own choice of tradeoffs.
Fourthly, I don't even like the SOT223 parts [160degC/W], let alone the tiny ones you're using. I
go for the NCP1117 DPAKs [67 degC/W].That looks like a nice part, but the problem is, that regulator doesn't have an enable pin, and the plan is to switch the motor and laser using the enable pin on the regulator.
Ok re on/off. I would still look around for another part, but that's just me/LOL. I'm sure they're there.
A lot of Arduino bds use the little SOT223 parts, and a few use the DPAK parts. Most don't even have a 3.3V reg. On
my own Arduino form factor pcb, I ended up with a TO220 5V reg and a DPAK 3.3V reg, both 1 Amp. That's my very
conservative idea of "general-purpose", where anyone using it will be less likely to burn the thing up.
At least you have some other considerations to think about. Good luck.
Last point, I might try buying 10 proto pcbs for $100 first, and try out the circuit, before jumping in and
buying 1000 bds.