Power down completely

[charlespax]

Does LabWiz ever power down completely or just go into a deep sleep mode? There are no power switching components.

Here is a power switching example. It has a pushbutton (SW2) to power on. Once on, the microcontroller needs to keep the power on via POWER_ON. The micro can also sense the state of the pushbutton via POWER_PB. You can then detect if the switch is pressed again and perform a shutdown. The button can also be used. Short press for normal use, long press for power off.

[charlespax]

It has been suggested that we disconnect the battery with a MOSFET. By completely disconnecting the battery via MOSFET you don't have any leakage current (e.g. the battery sense divider, quiescent current of regulator, etc.). The tradeoff is complexity though. There may be a part that integrates all this functionality

[robojay]

Related items... The 3.3V regulator dropout voltage (MIC5219-3.3, max of 400mV at 150mA, or max of 600mV at a 500mA burst) should be taken into account with battery voltage state. How low do you want to run the battery? 3.3V + 0.4V = battery needs to be >= 3.7V, etc.

If you don't have a way to disconnect the battery, you will continue to run it down, potentially inflicting permanent damage to the battery.

[robojay]

Depending on your overall current requirements, there are parts around that integrate charging, battery disconnect, something like this: http://www.microchip.com/wwwproducts/en/MCP73871

[charlespax]

Li-Po discharge curve:

The Qduino (https://www.sparkfun.com/products/13614) uses the AP2112K-3.3TRG1 (http://www.diodes.com/_files/datasheets/AP2112.pdf).

AP2112K output voltage vs input voltage:

I think this part will take care of us pretty well. We can get our 3.3V all the way down to a battery voltage of 3.3V.

Regulator swapped.

[charlespax]

The Qduino also has autoswitching between battery and USB:

I've incorporated that design:

Still need to add the ability to toggle the enable pin.