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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 VIN
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 VIN 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
MAX1971
COMP1
LX1
FB1
COMP2
FBSEL1
LX2
FB2
FBSEL2
REF
PGND
POR
OUT1
1.8V
750mA
OUT2
2.5V
750mA
LX1 1
VCC 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
For pricing, delivery, and ordering information, please contact Maxim Direct at 1-888-629-4642,
or visit Maxim’s website at www.maxim-ic.com.

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Dual, 180° Out-of-Phase, 1.4MHz, 750mA Step-
Down Regulator with POR and RSI/PFO
ABSOLUTE MAXIMUM RATINGS
IN, EN, FBSEL1, FBSEL2, PFO, POR,
RSI, VCC to GND ...................................................-0.3V to +6V
COMP1, COMP2, FB1, FB2,
REF to GND .............................................-0.3V to (VCC + 0.3V)
LX1, LX2 to PGND .......................................-0.3V to (VIN + 0.3V)
PGND to GND .......................................................-0.3V to +0.3V
Continuous Power Dissipation (TA = +70°C)
16-Pin QSOP (derate 8.3mW/°C above +70°C)...........667mW
Operating Temperature Range ...........................-40°C to +85°C
Storage Temperature Range .............................-65°C to +150°C
Lead Temperature (soldering, 10s) .................................+300°C
Stresses beyond those listed under “Absolute Maximum Ratings” may cause permanent damage to the device. These are stress ratings only, and functional
operation of the device at these or any other conditions beyond those indicated in the operational sections of the specifications is not implied. Exposure to
absolute maximum rating conditions for extended periods may affect device reliability.
ELECTRICAL CHARACTERISTICS
(VIN = VCC = VEN = 5V, R POR = 100kto IN, RPFO = 100kto IN, VRSI = 0, CREF = 0.1µF, FBSEL1 = unconnected, FBSEL2 =
unconnected, TA = 0°C to +85°C, unless otherwise noted. Typical values are at TA = +25°C.)
PARAMETER
IN AND VCC
IN Voltage Range
IN Supply Current
IN Shutdown Current
VCC Undervoltage
Lockout Threshold
REF
REF Voltage
REF Shutdown Resistance
REF Soft-Start Current
FB1 AND FB2
CONDITIONS
Switching with no load
VIN = 3.3V
VIN = 5.5V, VEN = 0
VCC rising
VCC falling
MAX1971
MAX1970/MAX1972
MAX1970/MAX1972
MAX1971
IREF = 0, VIN = 2.6V to 5.5V
REF to GND, VEN = 0
VREF = 1V
MIN TYP MAX UNITS
2.6 5.5 V
5 10
mA
10 20
1 100
µA
1 60
2.40 2.55
2.20 2.35
V
1.188
20
1.200
10
25
1.212
25
30
V
µA
FB_ Regulation Voltage
OUT_ Voltage Range
OUT1 Regulation Voltage
OUT2 Regulation Voltage
Maximum Output Current
FB1 Input Resistance
FB2 Input Resistance
FB_ Input Bias Current
FBSEL_ = unconnected, OUT1 = FB1, OUT2 = FB2,
VCOMP_ = 1.20V to 1.80V, VIN = 2.6V to 5.5V
FBSEL_ = unconnected
VIN = 2.6V to 5.5V
VCOMP1 = 1.2V, FBSEL1= GND
VIN = 4.5V to 5.5V
VCOMP1 = 1.2V, FBSEL1 = VCC
VIN = 2.6V to 5.5V
VCOMP2 = 1.2V, FBSEL2 = GND
VCOMP2 = 1.2V, FBSEL2 = VCC
Guaranteed by design (Note 1)
Measured from FB1 to
GND
Measured from FB2 to
GND
FBSEL1 = GND
FBSEL1 = VCC
FBSEL2 = GND
FBSEL2 = VCC
FB1 or FB2, FBSEL_ = unconnected, VFB1 = VFB2 = 1.15V
1.188 1.200
1.2
1.782
3.2670
1.485
2.475
750
30
30
22.5
22.5
1.800
3.3
1.5
2.5
60
60
45
45
0.01
1.212
VIN
1.818
3.330
1.150
2.525
120
120
90
90
0.1
V
V
V
V
mA
k
k
µA
2 _______________________________________________________________________________________

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Dual, 180° Out-of-Phase, 1.4MHz, 750mA Step-
Down Regulator with POR and RSI/PFO
ELECTRICAL CHARACTERISTICS (continued)
(VIN = VCC = VEN = 5V, R POR = 100kto IN, RPFO = 100kto IN, VRSI = 0, CREF = 0.1µF, FBSEL1 = unconnected, FBSEL2 =
unconnected, TA = 0°C to +85°C, unless otherwise noted. Typical values are at TA = +25°C.)
PARAMETER
CONDITIONS
MIN TYP MAX UNITS
COMP1 AND COMP2
COMP1
Transconductance
FB1 = COMP1,
VCOMP1 = 1.2V
FBSEL1 = unconnected
35 55 85 µS
COMP2
Transconductance
LX1 AND LX2
FB2 = COMP2,
VCOMP2 = 1.2V
FBSEL2 = unconnected
35 55 85 µS
Internal High-Side
MOSFET On-Resistance
ILX = -180mA
Internal Low-Side
MOSFET On-Resistance
LX_ Current-Sense
Transresistance
ILX = 180mA
VIN = 5.0V
VIN = 3.3V
VIN =2.6V
VIN = 5.0V
VIN = 3.3V
VIN = 2.6V
0.20
0.24
0.28
0.12
0.14
0.16
0.32
0.37
0.23
0.25
0.4 0.5 0.6 V/A
LX_ Current-Limit
Threshold
LX_ Leakage Current
Duty Cycle = 100%,
VIN = 2.6V to 5.5V
VIN = 5.5V
LX_ Switching Frequency VIN = 2.6V to 5.5V
High side
Low side
VLX1 = VLX2 = 5.5V
VLX1 = VLX2 = 0
MAX1970/MAX1972
MAX1971
0.80
-1.6
-20
1.2
0.60
1.2
-0.85
1.4
0.70
1.60
-0.40
20
1.6
0.80
A
µA
MHz
LX_ Maximum Duty Cycle
LX_ Minimum Duty Cycle
POR
VIN = 2.6V to 5.5V
MAX1970/MAX1972
MAX1971
100 %
15 20
%
10 15
POR Thresholds
POR Delay Time (TD)
POR Output Current, High
POR Output Voltage, Low
POR Startup Voltage
Percentage of VOUT,
VIN = 2.6V to 5.5V
VOUT rising
VOUT falling
MAX1970
MAX1971/MAX1972
VPOR = VIN = 5.5V, VFB1 = VFB2 = 1.15V
VFB1 = 1.05V or VFB2 = 1.05V or RSI = IN (MAX1971 only),
I POR = 1mA
FB1 = FB2 = GND, IPOR = 100µA, VIN = 1.2V
87
13.3
140
-1
92
90
16.6
175
0.01
0.01
94
20
210
1
0.05
0.05
%
ms
µA
V
V
_______________________________________________________________________________________ 3

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Dual, 180° Out-of-Phase, 1.4MHz, 750mA Step-
Down Regulator with POR and RSI/PFO
ELECTRICAL CHARACTERISTICS (continued)
(VIN = VCC = VEN = 5V, R POR = 100kto IN, RPFO = 100kto IN, VRSI = 0, CREF = 0.1µF, FBSEL1 = unconnected, FBSEL2 =
unconnected, TA = 0°C to +85°C, unless otherwise noted. Typical values are at TA = +25°C.)
PARAMETER
CONDITIONS
MIN TYP MAX UNITS
PFO (MAX1970 and MAX1972 Only)
PFO Trip Threshold
IN = VCC
VCC rising
VCC falling
PFO Output Current, High PFO = IN
PFO Output Voltage, Low IPFO = 1mA, VIN = 4.3V
EN AND RSI (MAX1971 Only)
Logic Input Thresholds
IN = 2.6V to 5.5V
VIL
VIH
RSI Input Resistance
Internal pullup resistor to IN
EN Logic Input Current
Logic input at 0 or
5.5V, VIN = 5.5V
VIL
VIH
3.86
-1
0.4
5
-1
-1
4.04
3.94
0.01
0.95
1.0
10
4.12
1
0.05
1.6
20
1
1
V
µA
V
V
k
µA
ELECTRICAL CHARACTERISTICS
(VIN = VCC = VEN = 5V, VFB1 = VFB2 = 1.15V, R POR = 100kto IN, RPFO = 100kto IN, RSI = 0, CVCC = 0.1µF, CREF = 0.1µF,
FBSEL1 = unconnected, FBSEL2 = unconnected, TA = -40°C to +85°C.) (Note 2)
PARAMETER
IN AND VCC
IN Voltage Range
IN Supply Current
IN Shutdown Current
VCC Undervoltage
Lockout Threshold
REF
REF Voltage
REF Shutdown Resistance
REF Soft-Start Current
FB1 AND FB2
CONDITIONS
Switching with no load
VIN = 3.3V
VIN = 5.5V, VEN = 0
VCC rising
VCC falling
MAX1971
MAX1970/MAX1972
MAX1970/MAX1972
MAX1971
IREF = 0, VIN = 2.6V to 5.5V
REF to GND, VEN=0
VREF = 1V
MIN TYP MAX UNITS
2.6 5.5 V
10
mA
20
20
µA
100
2.55
V
2.20
1.185
20
1.212
25
30
V
µA
FB_ Regulation Voltage
OUT_ Voltage Range
OUT1 Regulation Voltage
OUT2 Regulation Voltage
Maximum Output Current
FBSEL_ = unconnected, OUT1 = FB1, OUT2 = FB2,
VCOMP_ = 1.20V to 1.80V, VIN = 2.6V to 5.5V
FBSEL_ = unconnected
VIN = 2.6V to 5.5V
VCOMP1 = 1.2V, FBSEL1= GND
VIN = 4.5V to 5.5V
VCOMP1 = 1.2V, FBSEL1 = VCC
VIN = 2.6V to 5.5V
VCOMP2 = 1.2V, FBSEL2 = GND
VCOMP2 = 1.2V, FBSEL2 = VCC
Guaranteed by design (Note 1)
1.185
1.2
1.778
3.259
1.481
2.469
750
1.212
VIN
1.818
3.333
1.515
2.525
V
V
V
V
mA
4 _______________________________________________________________________________________

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Dual, 180° Out-of-Phase, 1.4MHz, 750mA Step-
Down Regulator with POR and RSI/PFO
ELECTRICAL CHARACTERISTICS (continued)
(VIN = VCC = VEN = 5V, VFB1 = VFB2 = 1.15V, R POR = 100kto IN, RPFO = 100kto IN, RSI = 0, CVCC = 0.1µF, CREF = 0.1µF,
FBSEL1 = unconnected, FBSEL2 = unconnected, TA = -40°C to +85°C.) (Note 2)
PARAMETER
FB1 Input Resistance
FB2 Input Resistance
FB_ Input Bias Current
COMP1 AND COMP2
CONDITIONS
Measured from FB1 to
GND
Measured from FB2 to
GND
FBSEL1 = GND
FBSEL1 = VCC
FBSEL2 = GND
FBSEL2 = VCC
FB1 or FB2, FBSEL_ = unconnected, VFB1 = VFB2 = 1.15V
MIN
30
30
22.5
22.5
TYP
MAX
120
120
90
90
0.1
UNITS
k
k
µA
COMP1
Transconductance
FB1 = COMP1,
VCOMP1 = 1.2V
FBSEL1 = unconnected
35
85 µS
COMP2
Transconductance
LX1 AND LX2
Internal High-Side
MOSFET On-Resistance
Internal Low-Side
MOSFET On-Resistance
LX_ Current-Sense
Transresistance
FB2 = COMP2,
VCOMP2 = 1.2V
ILX = -180mA
ILX = 180mA
FBSEL2 = unconnected
VIN = 5.0V
VIN = 3.3V
VIN = 5.0V
VIN = 3.3V
35
0.4
85 µS
0.32
0.37
0.23
0.25
0.6 V/A
LX_ Current-Limit
Threshold
LX_ Leakage Current
LX_ Switching Frequency
LX_ Minimum Duty Cycle
POR
POR Thresholds
POR Delay Time (TD)
POR Output Current, High
POR Output Voltage, Low
POR Start-Up Voltage
Duty cycle = 100%,
VIN = 2.6V to 5.5V
VIN = 5.5V
VIN = 2.6V to 5.5V
VIN = 2.6V to 5.5V
High side
Low side
VLX1 = VLX2 = 5.5V
VLX1 = VLX2 = 0
MAX1970/MAX1972
MAX1971
MAX1970/MAX1972
MAX1971
Percentage of VOUT,
VIN = 2.6V to 5.5V
MAX1970
VOUT rising
VOUT falling
MAX1971/MAX1972
V POR = VIN = 5.5V, VFB1 = VFB2 = 1.15V
VFB1 = 1.05V or VFB2 = 1.05V or RSI = IN (MAX1971 only),
IPOR = 1mA
FB1 = FB2 = GND, IPOR = 100µA, VIN = 1.2V
0.76
-1.6
-20
1.2
0.60
87
13.3
140
-1
1.60
-0.40
20
1.6
0.80
20
15
A
µA
MHz
%
94
%
20
ms
210
1 µA
0.05 V
0.05 V
_______________________________________________________________________________________ 5