The MAX1535B is a highly integrated, multichemistry battery charger that simplifies construction of advanced smart chargers with a minimum number of external components. It uses Intel's system management bus (SMBusTM) to control the charge voltage, charge current, and the maximum current drawn from the AC adapter. High efficiency is achieved through use of a constant offtime step-down topology with synchronous rectification. In addition to support of the Smart Battery Charger Specifications Rev 1.1, the MAX1535B includes additional features. The maximum current drawn from the AC adapter is programmable to avoid overloads when supplying the load and the battery charger simultaneously. This enables the user to reduce the cost of the AC adapter. The MAX1535B provides a digital output that indicates the presence of an AC adapter. Based on the presence or absence of the AC adapter, the MAX1535B automatically selects the appropriate source for supplying power to the system by controlling two external p-channel MOSFETs. Under system control, the MAX1535B allows the battery to undergo a relearning or conditioning cycle in which the battery is completely discharged through the system load and then recharged.