Running straight off Battery vs LDO

[cde 334]

Found a nice app note by TI, and wrote some thoughts on it:
 
Just recently read an app note that targets your same circumstances. Using power solutions to extend battery life in MSP430 applications By TI's Michael Day. While it uses the MSP430 as its target, the same applies to any MCU.
 
Depending on the MCU's Current vs Voltage, and Voltage vs Clock Speed, using an LDO with a low Quiescent Current will be much better than powering the MCU directly off the battery. The example uses 2x AA, and a TPS780xx regulator with 0.5

[Fmilburn 445]

I read the same app note right after I decided to make my nRF24 radio pcb run directly off 2xAA batteries.  Maybe that was a good idea and not just a money saver after all.

[spirilis 1,265]

That is a good idea, I recall TI mentioning this app note on twitter a while back. Of course remember the FET... the professional MSP-FET has pins to drive the level shifter to support low voltage use but a LaunchPad might be different.

[abecedarian 330]

Interesting read.

 

I have a FR6989 launchpad running the default program in temp mode, powered by a 3.6V NiCD cordless phone pack that was charged to about 2.6V. It was connected to the 3v3/GND pins at the lower right of the LP for a few days, then removed for a day so the V would settle, and the jumpers from the ICDI were removed so it didn't power those when running. It has been running continuously since 8am Feb 18, so that's about 8 days / 192 hours on the pack as of 8am this morning, or about 200 hours as of this moment.

 

No doubt a few, cheap solar panels would extend the run time by at least an order of magnitude... as would modifying the stock code to take advantage of the processor's low power abilities.