The BQ24810 device automatically switches adapter or battery power to system. An automatic break-before-make logic prevents shoot-through currents when the selectors switch. The system is powered across the body diode of the BATFET during the brief period between the first selector turning off and the second turning on.

The ACDRV drives a pair of common-source (CMSRC) N-channel power MOSFETs (ACFET and RBFET) between the adapter and ACP. The ACFET separates adapter from system and battery, and limits inrush current when the adapter is plugged in by controlling the ACFET turn-on time. Additionally, it protects the adapter when the system or battery is shorted. The RBFET provides negative input voltage protection and battery discharge protection when adapter is shorted to ground, and minimizes system power dissipation with its low R_DS(on) compared to a Schottky diode.

When the voltage measured at the ACDET pin is less than 2.4 V, it is determined that a valid adapter is not present. Under this condition, ACDRV is pulled to CMSRC to keep ACFET and RBFET off, isolating the adapter input from the system rail. BATDRV stays at V_BATSRC + 6 V to connect battery to system if all of the following conditions are valid:

• V_VCC > V_UVLO
• V_ACN < V_SRN + 200 mV
• ACFET/RBFET off

When the voltage measured at the ACDET pin is greater than 2.4 V, a valid adapter is determined to be present. Under this condition, the ACDRV is driven above CMSRC to turn ACFET and RBFET on, and the system power source switches from battery to adapter if all of the following conditions are valid:

• ACOK high with all conditions in Section 6.3.1.2 valid.
• Not in LEARN mode
• In LEARN mode and V_SRN < battery depletion threshold

The gate drive voltage on ACFET and RBFET is V_CMSRC + 6 V. If the ACFET/RBFET have been turned on for 20 ms, and the voltage across gate and source is still less than 5.7 V, ACFET and RBFET are turned off. After 1.3 sec delay, it resumes turning on ACFET and RBFET. If such a failure is detected seven times within 90 seconds, ACFET/RBFET are latched off and an adapter removal is required to force ACDET < 0.6 V to remove the latch. After the latch is reset, ACFET/RBFET can be turned on again.

To turn off ACFET/RBFET, one of the following conditions must be valid:

• In LEARN mode and V_SRN is above battery depletion threshold;
• ACOK low

To limit the adapter inrush current during ACFET turn-on, the Cgs and Cgd external capacitor of ACFET must be carefully selected following the guidelines below:

• Minimize total capacitance on system
• Cgs should be 40× or higher than Cgd to avoid ACFET false turn on during adapter hot plug-in
• Fully turn on ACFET within 20 ms, otherwise, charger IC will consider turn-on failure
• Check with MOSFET vendor on peak current rating
• Place 4-kΩ resistor in series with ACDRV, CMSRC, and BATDRV pin to limit inrush current