10 Nov 2012: AXP209 Real Time Clock Power Out
The AXP209 is an awesome Power Management IC - the only problem is that the datasheet is in Chinese, and an automatic translation doesn't help much either. It turns out however that the AXP209 not only does several LDOs and a couple of DC-DC conversions, but also does battery charging, battery monitoring, USB-OTG detection for power and battery charging as well, and AC power input as well! The only thing is that some help is needed to double-check the datasheet to ensure that it the LDO1 has been set to output 3.3V. The STM32F's RTC battery input requires a minimum of 2.0V, and it appears that if LDO1SET is pulled to GND the output of LDO1 is set to 1.3V.