Power supplies will start-up when:
SYS_CTRL goes high (from below 0.4V to above 1.6V)
Battery is attached (VBAT goes from below 0.4V to above 2.8V)
Charger is attached (VCHG does from below 0.4V to above 3.6V)
To meet requirements of USB specification, the chip decides which power input to boot from as follows:
When VBAT > 3.3V then battery is considered good and chip boots from VBAT
−In this case it does not matter what voltage is on VCHG
When VCHG > 3.6V (charger present) and VBAT < 3.3V then battery is considered weak and chip boots from VCHG
When VCHG < 3.6V (charger not present) and chip boots from VBAT as long as VBAT> 2.6V
When VCHG < 3.6V and VBAT < 2.6V then there is no good power source and the chip does not boot
−This is to prevent over-discharging the battery
−The start-up circuit will continue to consume ~100μA until boot stimulus is removed, but the chip will not start
All voltage thresholds are ±5%