The MAX1645 is a high-efficiency battery charger capable of charging batteries of any chemistry type. It uses the Intel System Management Bus (SMBusTM) to control voltage and current charge outputs. When charging lithium-ion (Li+) batteries, the MAX1645 automatically transitions from regulating current to regulating voltage. The MAX1645 can also limit line input current so as not to exceed a predetermined current drawn from the DC source. A 175sec charge safety timer prevents "runaway charging" should the MAX1645 stop receiving charging voltage/current commands. The MAX1645 employs a next-generation synchronous buck control circuitry that lowers the minimum input-tooutput voltage drop by allowing the duty cycle to exceed 99%. The MAX1645 can easily charge one to four series Li+ cells.