Difficulty in VReg selection

[aurmer]

My Mouser search powers are failing me. Or is my ELEN 101 why I fail?? What type of Voltage Regulator am I looking for with these requirements? I started with looking LDO Vregs, but all I was finding were ones that change Vout based on Vin. Does such a thing exist?

Requirements:
Iout: 150mA sustained (even 100mA sustained?)
Vin: 3.3V - 5V (as low as 3.3V isn't realistic, but trying to go as low as possible for 'acceptable Vin' because backup battery is 3 AA cells. The lower it will accept power, the longer it can run on battery.)
Vout: 3.3V - constant across Vin range.

[Jeroen3]

LDO's wil always drop some voltage. And they often turn off when Vin < Vout+1.
You could use a buck-boost regulator. Such as: TPS63060.