Maxim Integrated Products Inc. (Sunnyvale, CA) announced the MAX1873, which provides precise voltage and current regulation for lithium-ion battery charger applications for two-, three-, and four-cell notebook and Internet tablet systems. The MAX1873 also allows the thermal and time monitoring to be done by the system's microprocessor and/or keyboard controller, eliminating the need for a synchronous rectifier to implement its step-down dc/dc configuration.
The MAX1873 includes an input-current control loop, which monitors the total draw from the ac adapter. If the sum of the system and charging currents exceeds the current rating of the wall adapter, the charging current is reduced, allowing the use of a low-cost adapter.
The MAX1873 charges lithium-ion batteries using a standard voltage-limited current-source method. The device is offered with three different preset output-voltage options: the MAX1873R is set for two cells, the MAX1873S for three cells and the MAX1873T for four cells.
With an input-voltage range up to 28V, the MAX1873 operates down to only 200mV dropout at 100-percent duty cycle. The output-voltage tolerance is ±0.75 percent, and the current limit is adjustable with a single resistor. The switching pass element is a single external p-channel MOSFET, pulse-width modulated at 300kHz constant frequency. This allows for easy filtering and the use of small components. Shutdown current is only 5µA.
The MAX1873 provides an optional analog output proportional to the charge current for use as a charge-current gauge. When paired with a microprocessor, the MAX1873 can also be used as a current source for charging 5 to 10 NiMH or NiCd batteries.
