The IC automatically switches adapter or battery power to the system load. The battery is connected to the system by default during power up or during SLEEP mode. When the adapter plugs in and the voltage is above the battery voltage, the IC exits SLEEP mode. The battery is disconnected from the system and the adapter is connected to the system after exiting SLEEP. An automatic break-before-make logic prevents shoot-through currents when the selectors switch.

The ACDRV is used to drive a pair of back-to-back N-channel power MOSFETs between adapter and ACP with sources connected together to CMSRC. The N-channel FET with the drain connected to the ACP (Q2, RBFET) provides reverse battery discharge protection, and minimizes system power dissipation with its low-RDS_ON. The other N-channel FET with drain connected to adapter input (Q1, ACFET) separates battery from adapter, and provides a limited dI/dt when connecting the adapter to the system by controlling the FET turnon time. The /BATDRV controls a P-channel power MOSFET (Q3, BATFET) placed between battery and system with drain connected to battery.

Before the adapter is detected, the ACDRV is pulled to CMSRC to keep ACFET off, disconnecting the adapter from system. /BATDRV stays at ACN - 6 V (clamp to ground) to connect battery to system if all the following conditions are valid:

• V_AVCC > V_UVLO (battery supplies AVCC)
• V_ACN < V_SRN + 200 mV

After the device comes out of SLEEP mode, the system begins to switch from battery to adapter. The AVCC voltage has to be 300 mV above SRN to enable the transition. The break-before-make logic keeps both ACFET and BATFET off for 10 µs before ACFET turns on. This prevents shoot-through current or any large discharging current from going into the battery. The /BATDRV is pulled up to ACN and the ACDRV pin is set to CMSRC +
6 V by an internal charge pump to turn on N-channel ACFET, connecting the adapter to the system if all the following conditions are valid:

• V_ACUV < V_OVPSET < V_ACOV
• V_AVCC > V_SRN + 300 mV

When the adapter is removed, the IC turns off ACFET and enters SLEEP mode.

BATFET keeps off until the system drops close to SRN. The BATDRV pin is driven to ACN - 6V by an internal regulator to turn on P-channel BATFET, connecting the battery to the system.

Asymmetrical gate drive provides fast turnoff and slow turnon of the ACFET and BATFET to help the break-before-make logic and to allow a soft-start at turnon of both MOSFETs. The delay time can be further increased, by putting a capacitor from gate to source of the power MOSFETs.