General Description
The MAX649/MAX651/MAX652 BiCMOS, step-down DC-DC switching controllers provide high efficiency over three decades of load current. A unique, current-limited pulse-frequency-modulated (PFM) control scheme gives these devices the benefits of pulse-width-modulation (PWM) converters (high efficiency at heavy loads), while using only 100µA of supply current (vs. 2mA to 10mA for PWM converters). The result is high efficiency over loads ranging from 10mA to more than 2.5A.
These devices use miniature external components. Their high switching frequency (up to 300kHz) allows for less than 9mm diameter surface-mount inductors.
The MAX649/MAX651/MAX652 have dropout voltages less than 1V and accept input voltages up to 16.5V. Output voltages are preset at 5V (MAX649), 3.3V (MAX651), and 3V (MAX652). These controllers can also be adjusted to any voltage from 1.5V to the input voltage by using two resistors.
These step-down controllers drive external P-channel MOSFETs at loads greater than 10W. If less power is required, use the MAX639/MAX640/MAX653 step-down converters with on-chip FETs, which allow up to a 225mA load current.

Features
♦ More than 90% Efficiency (10mA to 1.5A Loads)
♦ More than 12.5W Output Power
♦ 100µA Max Quiescent Supply Current
♦ 5µA Max Shutdown Supply Current
♦ Less than 1.0V Dropout Voltage
♦ 16.5V Max Input Voltage
♦ 5V (MAX649), 3.3V (MAX651), 3V (MAX652), or Adjustable Output Voltage
♦ Current-Limited Control Scheme
♦ Up to 300kHz Switching Frequency

Applications
   5V-to-3.3V Green PC Applications
   High-Efficiency Step-Down Regulation
   Minimum-Component DC-DC Converters
   Battery-Powered Applications