I'm working on a project with a micro and some accessories like a really small OLED, accelerometer, and maybe even a uSD card reader (space and power permitting). I'm trying to decide on an approach to best power everything and I'd appreciate input. The entire system will be 3.3V and run from lithium. I'd like the micro to always be powered but cut power to the accessories completely when the micro sleeps for power savings and to be able to reset them in case of things like I2C bus hang/issues.
Major Objectives (In Priority Order) Small footprint / fewest components Low power consumption during micro sleep Cost
Approach 1 A 2-channel 3V3 LDO with low quiescent current like the AP7312 (http://diodes.com/datasheets/AP7312.pdf) will be used. Channel 1 will have the enable pin always active (tired to VBAT) and used to power the micro at all times. Channel 2 will be inactive (pull-down) and driven high only when the micro is awake to power the accessories.
Approach 2 A larger single-channel 3V3 LDO used to power the entire circuit. A MOSFET will be used to enable power to the accessories with the gate enabled online while the micro is awake.
Approach 3 Something I haven't thought of? Since they're only 1mA each maybe just driving them using the micro's GPIO? This wouldn't work if I implement a uSD socket though as it draws too much current but could be viable for the OLED/accelerometer only.