LOWEST COST SWITCH-MODE Li+ CHARGER INCLUDES INPUT-CURRENT-LIMITING LOOP
SUNNYVALE, CA-September 4, 2001-Maxim Integrated Products introduces the MAX1873, which is the simplest and lowest cost lithium ion (Li+) battery charger for 2-, 3-, and 4-cell notebook and Internet tablet systems. It provides precise voltage and current regulation, and sheds cost by allowing the thermal and time monitoring to be done by the system’s microprocessor and/or keyboard controller and by not requiring a synchronous rectifier to implement its step-down DC-DC configuration. The MAX1873 also 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 that need not be overspecified.
The MAX1873 charges Li+ batteries using a standard voltage-limited current-source method. Available with three different preset output-voltage options to save the cost of external components, the MAX1873R is set for 2 Li+ cells, MAX1873S for 3 Li+ cells, and MAX1873T for 4 Lit+ cells.
With an input voltage range up to 28V, the device operates down to only 200mV dropout at 100% duty cycle to accommodate low-cost, loosely regulated AC adapters. The output voltage tolerance is ±0.75%, and the current limit is adjustable with a single resistor. The switching pass element is a single external P-channel MOSFET, which is pulse-width modulated (PWM) at a constant frequency of 300kHz to allow easy filtering and 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.
The MAX1873REEE, MAX1873SEEE, and MAX1873TEEE come in 16-pin QSOP packages and are screened for the extended-industrial temperature range (-40°C to +85°C). Prices start at $1.98 (1000-up, U.S. recommended resale). The MAX1873 evaluation kit is available to speed designs.
|
