2A, Low-Voltage, Step-Down Regulator with Synchronous Rectification and Internal Switches

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%.

The MAX1644 uses a unique current-mode, constant-off-time, PWM control scheme, which includes an Idle Mode™ to maintain high efficiency during light-load operation. The programmable constant-off-time architecture sets switching frequencies up to 350kHz, allowing the user to optimize performance trade-offs between efficiency, output switching noise, component size, and cost. The device also features an adjustable soft-start to limit surge currents during start-up, a 100% duty cycle mode for low-dropout operation, and a low-power shutdown mode that disconnects the input from the output and reduces supply current below 1µA. The MAX1644 is available in a 16-pin SSOP package.

Applications

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

* ±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