An external resistor voltage divider attenuates the adapter voltage to the ACDET pin. The adapter detect threshold should typically be programmed to a value greater than the maximum battery voltage and lower than the minimum-allowed adapter voltage. The ACDET divider should be placed before the ACFET in order to sense the true adapter input voltage whether the ACFET is on or off. Before the adapter is detected, BATFET stays on and ACFET turns off.

If PVCC is below 4 V, the device is disable.

If ACDET is below 0.6 V but PVCC is above 4 V, part of the bias is enabled, including a crude bandgap reference, ACFET drive and BATFET drive. IADAPT is disabled and pulled down to GND. The total quiescent current is less than 10 μA.

When ACDET rises above 0.6 V and PVCC is above 4 V, all the bias circuits are enabled and VREF goes to 3.3V. IF CHGEN is LOW, the REGN output rises to 6 V. IADAPT becomes valid to proportionally reflect the adapter current.

When ACDET keeps rising and passes 2.4 V, a valid AC adapter is present. 500 ms later, the following occurs:

• ACGOOD is pulled high through the external pull-up resistor to the host digital voltage rail;
• ACFET is allowed to turn on and BATFET turns off consequently; (refer to System Power Selector )
• Charging begins if all the conditions are satisfied and STAT becomes valid. (refer to Enable and Disable Charging )