Thanks guys, I appreciate your replies.
I don't think charge pump is a good solution, for 500mA it 'd be both - costly & inefficient.
I already advised two option:
1. ultra-low saturation BJT with LDO, it may squize battery down to 1-2V;
2. step-up/step-down in single chip. I was referring to TI as an example, probably there is low cost IC somewhere - google. If one chip is costly, than option with two IC is still on the table.
Don't know anything about EMI testing, never did.
I am using a lipo, it can't go below 3v. It has a range from 3.7 down to 3v. And I the only way to get the full 3v with an LDO is to bypass it once voltage reaches around 3.4 volts.
And I don't understand what you mean by using BJT with LDO.
If I can find a solution where I don't have to worry about EMI, I will go with step-up/step-down. I looked for metal shields, but didn't see any on digikey or mouser, but maybe I was just searching for the wrong thing.
Thanks
Edit: I found them, RF shield is what you need to search. Problem with those though, is they take up a lot of space, which I don't have.
Smallest one is also $1.50 on digikey, atleast for 1 unit.
Zener diodes require a considerable current to regulate properly and they're not even very well regulated.
Right, I hear you. I guess 10mA is more than I thought.
I've never worked with batteries where I had to be power conscious before.
Scrap the voltage regulator bypass idea. Only use the AP7215, to power the parts of the circuit which don't need much power and require a regulated power supply i.e. CPLD, ADC and MCU etc. The higher current stuff such as motors and any LEDs can be powered from an unregulated power supply, thus saving voltage drop and power dissipation.
I can't do that, my USB port will also some times be plugged into a 3.3v source, and if it is, I need to be able to bypass the regulator, or as MasterT said, use a Step-up/step-down regulator, which I'm really trying to avoid.
Yes I know all USB ports are 5v, but I am designing it so it can be plugged into something else, which is a must.
I could do the bypassing with the TPS3780, but its just going to add another $2 to my board.
Actually, I just realized I can use it for under voltage protection as well, at least I think I can.
It will allow me to drive a p-channel mosfet to shut off the circuit if it goes under 3v, and will pay for itself because I can take off the IC that handles that.
If you want the motor speed to be independent of supply voltage, then PWM the motor, monitor the unregulated rail, using a potential divider and adjust the duty cycle to compensate.
Good idea, but I actually do have Motors and LEDs setup with an N-channel for PWM.

I just took them off of the regulator, that I wasn't doing, I was trying to avoid the variable output, but I think most products on the market have that problem anyways.
So with PWM to avoid variable output, I would have the change the duty cycle depending on voltage, correct?
Thanks.
Don't regulate the DC motor supply - problem solved.
With lower current, very low drop-outs below 100mV are easily available.
Yes I will stop regulating it.
This is in my reply to Zero, its why I still need to bypass the regulator, I can't guarantee when the USB plug is in a 3.3v source, that it will be higher than 100mV.
I can't do that, my USB port will occasionally be plugged into a 3.3v source, and if it is, I need to be able to bypass the regulator, or as MasterT said, use a Step-up/step-down regulator, which I'm really trying to avoid.
Yes I know all USB ports are 5v, but I am designing it so it can be plugged into something else, which is a must.The only way I can not bypass the regulator, is if I make my MCU/CPLD run at 2.5v, which may be an option, I need to look into it further to make sure all the features I need can run at 2.5v, or if I use a step-up/step-down.
I know some MCU's cannot do USB at 2.7v, but I read that you may be able to use a level-shifter, and I already have level-shifter with more channels than I need. That still doesn't guarantee anything, but its a start.
Right now I'm really just trying to find the best cost/efficiency ratio, for bypassing the LDO.
Thanks.