MAX1970_09 Datasheet, PDF (1/21 Pages) Maxim Integrated Products – Dual, 180° Out-of-Phase, 1.4MHz, 750mA Step- Down Regulator with POR and RSI/PFO

19-2297; Rev 1; 2/09
Dual, 180° Out-of-Phase, 1.4MHz, 750mA Step-
Down Regulator with POR and RSI/PFO
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
xDSL Modems
xDSL Routers
Copper Gigabit SFP
and GBIC Modules
USB-Powered Devices
Dual LDO Replacement
Typical Operating Circuit
VIN 2.6V TO 5.5V
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
Ordering Information
PART
MAX1970EEE
MAX1971EEE
MAX1972EEE
TEMP RANGE
-40°C to +85°C
-40°C to +85°C
-40°C to +85°C
PIN-PACKAGE
16 QSOP
16 QSOP
16 QSOP
Pin Configuration
TOP VIEW
RSI
EN
VCC
RSI ^IN
VCC
POR
EN
LX1
MAX1971
COMP1
FB1
COMP2
LX2
FBSEL1
FB2
FBSEL2
REF
PGND
POR
OUT1
1.8V
750mA
OUT2
2.5V
750mA
LX1 1
V_CC 2
COMP1 3
FB1 4
FB2 5
COMP2 6
REF 7
GND 8
MAX1970
MAX1971
MAX1972
QSOP
16 PGND
15 LX2
14 IN
13 FBSEL1
12 FBSEL2
11
PF0 (MAX1970/MAX1972)
RSI (MAX1971)
10 EN
9 POR
________________________________________________________________ Maxim Integrated Products 1
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