The MAX1970/MAX1971/MAX1972 dual-output current-mode PWM buck regulators operate from 2.6V to 5.5V input and deliver a minimum of 750mA on each output. The MAX1970 and MAX1972 operate at a fixed 1.4MHz (MAX1971 operates at 700kHz) to reduce output inductor and capacitor size and cost. Switching the regulators 180° out-of-phase also reduces the input capacitor size and cost. Ceramic capacitors can be used for input and output.
The output voltages are programmable from 1.2V to V
IN using external feedback resistors, or can be preset to 1.8V or 3.3V for output 1 and 1.5V or 2.5V for output 2. When one output is higher than 1.2V, the second can be configured down to sub-1V levels. Output accuracy is better than ±1% over variations in load, line, and temperature. Internal soft-start reduces inrush current during startup.
All devices feature power-on reset (active-low POR). The MAX1971 includes a reset input (RSI), which forces active-low POR low for 175ms after RSI goes low. The MAX1970 and MAX1972 include an open-drain power-fail output (PFO) that monitors input voltage and goes high when the input falls below 3.94V. For USB-powered xDSL modems, this output can be used to detect USB power failure. A minimum switching frequency of 1.2MHz ensures operation outside the xDSL band.
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