The ISL9518, ISL9518A are highly integrated Narrow VDC system voltage regulators and battery charger controllers. Operating parameters are programmable over the System Management Bus (SMBus). The ISL9518, ISL9518A are designed for applications where the system power source is either the battery pack or the output of the regulator/charger. This makes the max voltage to the system equal to the max battery voltage instead of the max adapter voltage. The ISL9518, ISL9518A also include a system to control trickle charging deeply discharged batteries while maintaining system voltage at a user defined minimum. High efficiency is achieved with a DC/DC synchronous-rectifier buck converter, equipped with diode emulation for enhanced light load efficiency and AC-adapter boosting prevention. The ISL9518, ISL9518A can charge two to four series connected Lithium-ion cells, at up to 8A charge current. The ISL9518 has default settings for 2-cell systems and the ISL9518A has default settings for 3-cell systems. Integrated MOSFET drivers and bootstrap diode result in fewer components and smaller implementation area. Low offset current-sense amplifiers provide high accuracy. The ISL9518, ISL9518A provide two open drain digital outputs that indicate the presence of the AC adapter and trickle charge state. Trickle charge state and AC adapter present indicators are also available via SMBus. The ISL9518, ISL9518A also provide two analog outputs that indicate the adapter current and battery discharge current with 4% accuracy.