It's been a while since I've been on the forum, but I had a good look and can't find anything similar to my query.
I'm making an LED wrist-watch, using an MSP430G2102, after seeing some low power stuff it had been used for. The idea is that it's in a low power mode most of the time, only leaving sleep mode to increment the time, once a second, or when a button is pressed, activating the display for a few seconds after the last press.
I plan to run it off a single 3v coin cell, but as this voltage drops, the blue LEDs it's required to power might not even turn on. They are being Charliplexed, which for this problem, means that all of the LED current for this display is sourced and sunk from/into the MSP430 itself, rather than directly from a supply line. I would require a step-up DC/DC converter, but these aren't terribly efficient at low current draws (like the low power mode the device will spent most of its time in) and so I am planning to use the enable line on the DC/DC (
http://au.element14.com/jsp/search/productdetail.jsp?sku=1077152 ) to turn it on, and power the MSP430 only when the LEDs are required to be on.
I'm having difficulty designing a circuit which can use a single GPIO on the MSP430 to both disconnect the battery directly from supplying voltage to the MSP430 for its low-power mode, and turning on the SMPS when required. The more simple the external componentry is, the better, as I've got to solder the board by hand and think smaller/more elegant is better etc..
If anyone has done this before, or could help me out, that would be great! Thanks!