General Description
The MAX1809 is a reversible energy flow, constant-off-time, pulse-width modulated (PWM), step-down DC-DC converter. It is ideal for use in notebook and subnotebook computers that require 1.1V to 5V active termination power supplies. This device features an internal PMOS power switch and internal synchronous rectifier for high efficiency and reduced component count. The internal 90mΩ PMOS power switch and 70mΩ NMOS synchronous-rectifier switch easily deliver continuous load currents up to 3A. The MAX1809 accurately tracks an external reference voltage, produces an adjustable output from 1.1V to VIN, and achieves efficiencies as high as 93%.

Features
♦ Source/Sink 3A
♦ ±1% Output Accuracy
♦ Up to 1MHz Switching Frequency
♦ 93% Efficiency
♦ Internal PMOS/NMOS Switches
    90mΩ/70mΩ On-Resistance at VIN = 4.5V
    110mΩ/80mΩ On-Resistance at VIN = 3V
♦ 1.1V to VIN Adjustable Output Voltage
♦ 3V to 5.5V Input Voltage Range
♦ <1µA Shutdown Supply Current
♦ Programmable Constant-Off-Time Operation
♦ Thermal Shutdown
♦ Adjustable Soft-Start Inrush Current Limiting
♦ Output Short-Circuit Protection

Applications
    DDR Memory Termination
    Active Termination Buses