The device powers up from the higher voltage of VBUS or VBAT through integrated power selector. The charger starts POR (power on reset) when VBUS exceeds V_{VBUS_UVLOZ} or VBAT exceeds V_{VBAT_UVLOZ}. 5 ms after either VBUS or VBAT becomes valid, the charger resets all the registers to the default state. Another 5 ms later, the user registers become accessible to the host.

Power up sequence when the charger is powered up from VBUS:

• After VBUS above V_{VBUS_UVLOZ}, enable 6-V LDO REGN pin and VDDA pin voltage increase accordingly. CHRG_OK pin goes HIGH and the AC_STAT is configured to 1.
• After passing VBUS qualification, the REGN voltage is setup. VINDPM is detected in VBUS steady state voltage and IIN_DPM is detected at ILIM_HIZ pin steady state voltage.
• Battery CELL configuration is read at CELL_BATPRESZ pin voltage and compared to VDDA to determine cell configuration. Corresponding the default value of ChargeVoltage register (REG0x05/04()), ChargeCurrent register (Reg0x03/02), VSYS_MIN register (Reg0x0D/0C) and SYSOVP threshold are loaded.
• Converter powers up.

Power up sequence when the charger is powered up from VBAT:

• If only battery is present and the voltage is above V_{VBAT_UVLOZ} , charger wakes up and the BATFET is turned on and connecting the battery to system.
• By default, the charger is in low power mode (EN_LWPWR = 1b) with lowest quiescent current. The REGN LDO stays off. The Quiescent current is minimized. PROCHOT is available through the independent comparator by setting EN_PROCHOT_LPWR=1b.
• The adapter present comparator is activated, to monitor the VBUS voltage.
• SDA and SDL lines stand by waiting for host commands.
• Device can move to performance mode by configuring EN_LWPWR = 0b. The host can enable IBAT buffer through setting EN_IBAT=1b to monitor discharge current. The PSYS, PROCHOT or the independent comparator also can be enabled by the host.
• In performance mode, the REGN LDO is always available to provide an accurate reference and gate drive voltage for the converter.