General Description
The MAX1644 constant-off-time, PWM step-down DC-DC converter is ideal for use in applications such as PC cards, CPU daughter cards, and desktop computer bus-termination boards. The device features internal synchronous rectification for high efficiency and reduced component count. It requires no external Schottky diode. The internal 0.10Ω PMOS power switch and 0.10Ω NMOS synchronous-rectifier switch easily deliver continuous load currents up to 2A. The MAX1644 produces a preset +3.3V or +2.5V output voltage or an adjustable output from +1.1V to VIN. It achieves efficiencies as high as 95%.

Features
♦ ±1% Output Accuracy
♦ 95% Efficiency
♦ Internal PMOS and NMOS Switches
    70mΩ On-Resistance at VIN = +4.5V
    100mΩ On-Resistance at VIN = +3V
♦ Output Voltage
    +3.3V or +2.5V Pin-Selectable
    +1.1V to VIN Adjustable
♦ +3V to +5.5V Input Voltage Range
♦ 360µA (max) Operating Supply Current
♦ < 1µA Shutdown Supply Current
♦ Programmable Constant-Off-Time Operation
♦ 350kHz (max) Switching Frequency
♦ Idle Mode Operation at Light Loads
♦ Thermal Shutdown
♦ Adjustable Soft-Start Inrush Current Limiting
♦ 100% Duty Cycle During Low-Dropout Operation
♦ Output Short-Circuit Protection
♦ 16-Pin SSOP Package

Applications
    +5V to +3.3V/+2.5V Conversion
    CPU I/O Supply
    +3.3V PC Card and CardBus Applications
    Notebook and Subnotebook Computers
    Desktop Bus-Termination Boards
    CPU Daughter Card Supply