General Description
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 induc-
tor and capacitor size and cost. Switching the regula-
tors 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 tem-
perature. Internal soft-start reduces inrush current dur-
ing startup.
All devices feature power-on reset (POR). The
MAX1971 includes a reset input (RSI), which forces
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.
Applications
Features
o Current-Mode, 1.4MHz Fixed-Frequency PWM
Operation
o 180° Out-of-Phase Operation Reduces Input
Capacitor
o ±1% Output Accuracy Over Load, Line, and
Temperature Ranges
o 750mA Guaranteed Output Current
o 2.6V to 5.5V Input
o Power-On Reset Delay of 16.6ms (MAX1970) or
175ms (MAX1971 and MAX1972)
o Power-Fail Output (MAX1970 and MAX1972 Only)
o Power-On Reset Input (MAX1971 Only)
o Operation Outside xDSL Band
o Ultra-Compact Design with Smallest External
Components
o Outputs Adjustable from 0.8V to V
IN
or 1.8V/3.3V
and 1.5V/2.5V Preset
o All-Ceramic Capacitor Application
o Soft-Start Reduces Inrush Current
MAX1970/MAX1971/MAX1972
Dual, 180° Out-of-Phase, 1.4MHz, 750mA Step-
Down Regulator with POR and RSI/PFO
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Maxim Integrated Products
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