I think it is a type/ Basically the energy (U * I) out = eneryg going in corrected with inefiiciency losses. OS if the voltage goes down the current goes up.
I built a project recently myself where I have an ADXL345 (6 DoF sensor) running at 3.3V (constant in sleep mode) and a Tiny84 direct on the battery. The ADXL345 gets fed by the regulator. The nice thing about the linears is that they will push the Vin to Vout when Vin is below 3.3V + dropout. So the only reason for the regulator to work is as long as the battery voltage is above 3.3V (i am using 3 x AAA in series = 4.5V). Once it gest below the regulating voltage only a few uA's are lost in the regulator
There is a boost circuit (MCP1640) sleeping when everything else is (Boost is disabled).
Now when the ADXL345 detects a change in the axis (rotation), an interrupt wakes the CPU. That in turn reads the ADXL. If the direction change is relevant, the boost circuit is switched on. That in turn switches a 433 Mhz transmitter on and data is sent.
And then everything goes back to sleep. The whole process takes about 2 seconds (mostly because of some delays I think I need).
Current consumption:
- in sleepmode about 120uA.
- in activation 15 mA And that is including a LED.
Expected lifetime with average 3 x AAA batteries is more than a year.
The circuit has been running now for about 6 weeks with triple amount of activity on a daily basis. Voltage drop has been 3mV sofar 