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.
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
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
Applications
xDSL Modems
xDSL Routers
Copper Gigabit SFP
and GBIC Modules
USB-Powered Devices
Dual LDO Replacement
Typical Operating Circuit
V
IN
2.6V TO 5.5V
Pin Configuration
TOP VIEW
RSI
EN
RSI
EN
IN
V
CC
POR
POR
LX1
OUT1
1.8V
750mA
LX1 1
V
CC
2
COMP1 3
FB1 4
16 PGND
15 LX2
14 IN
MAX1971
COMP1
COMP2
V
CC
FBSEL1
FB1
LX2
FB2
OUT2
2.5V
750mA
FB2 5
COMP2 6
REF 7
MAX1970
MAX1971
MAX1972
13 FBSEL1
12 FBSEL2
PF0 (MAX1970/MAX1972)
11
RSI (MAX1971)
10 EN
9
POR
FBSEL2
REF
PGND
GND 8
QSOP
________________________________________________________________
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.
Dual, 180° Out-of-Phase, 1.4MHz, 750mA Step-
Down Regulator with POR and RSI/PFO
MAX1970/MAX1971/MAX1972
ABSOLUTE MAXIMUM RATINGS
IN, EN, FBSEL1, FBSEL2, PFO,
POR,
RSI, V
CC
to GND ...................................................-0.3V to +6V
COMP1, COMP2, FB1, FB2,
REF to GND .............................................-0.3V to (V
CC
+ 0.3V)
LX1, LX2 to PGND .......................................-0.3V to (V
IN
+ 0.3V)
PGND to GND .......................................................-0.3V to +0.3V
Continuous Power Dissipation (T
A
= +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
(V
IN
= V
CC
= V
EN
= 5V, R
POR
= 100kΩ to IN, R
PFO
= 100kΩ to IN, V
RSI
= 0, C
REF
= 0.1µF, FBSEL1 = unconnected, FBSEL2 =
unconnected,
T
A
= 0°C to +85°C,
unless otherwise noted. Typical values are at T
A
= +25°C.)
PARAMETER
IN AND V
CC
IN Voltage Range
IN Supply Current
IN Shutdown Current
V
CC
Undervoltage
Lockout Threshold
REF
REF Voltage
REF Shutdown Resistance
REF Soft-Start Current
FB1 AND FB2
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,
V
COMP_
= 1.20V to 1.80V, V
IN
= 2.6V to 5.5V
FBSEL_ = unconnected
V
IN
= 2.6V to 5.5V
V
IN
= 4.5V to 5.5V
V
IN
= 2.6V to 5.5V
V
COMP1
= 1.2V, FBSEL1= GND
V
COMP1
= 1.2V, FBSEL1 = V
CC
V
COMP2
= 1.2V, FBSEL2 = GND
V
COMP2
= 1.2V, FBSEL2 = V
CC
FBSEL1 = GND
FBSEL1 = V
CC
FBSEL2 = GND
FBSEL2 = V
CC
1.188
1.2
1.782
3.2670
1.485
2.475
750
30
30
22.5
22.5
60
60
45
45
0.01
120
120
90
90
0.1
1.800
3.3
1.5
2.5
1.200
1.212
V
IN
1.818
3.330
1.150
2.525
V
V
V
V
mA
kΩ
kΩ
µA
I
REF
= 0, V
IN
= 2.6V to 5.5V
REF to GND, V
EN
= 0
V
REF
= 1V
20
1.188
1.200
10
25
1.212
25
30
V
Ω
µA
Switching with no load
V
IN
= 3.3V
V
IN
= 5.5V, V
EN
= 0
V
CC
rising
V
CC
falling
2.20
MAX1971
MAX1970/MAX1972
MAX1970/MAX1972
MAX1971
2.6
5
10
1
1
2.40
2.35
5.5
10
20
100
60
2.55
V
mA
µA
V
CONDITIONS
MIN
TYP
MAX
UNITS
Guaranteed by design (Note 1)
Measured from FB1 to
GND
Measured from FB2 to
GND
FB1 or FB2, FBSEL_ = unconnected, V
FB1
= V
FB2
= 1.15V
2
_______________________________________________________________________________________
Dual, 180° Out-of-Phase, 1.4MHz, 750mA Step-
Down Regulator with POR and RSI/PFO
ELECTRICAL CHARACTERISTICS (continued)
(V
IN
= V
CC
= V
EN
= 5V, R
POR
= 100kΩ to IN, R
PFO
= 100kΩ to IN, V
RSI
= 0, C
REF
= 0.1µF, FBSEL1 = unconnected, FBSEL2 =
unconnected,
T
A
= 0°C to +85°C,
unless otherwise noted. Typical values are at T
A
= +25°C.)
PARAMETER
COMP1 AND COMP2
COMP1
Transconductance
COMP2
Transconductance
LX1 AND LX2
Internal High-Side
MOSFET On-Resistance
V
IN
= 5.0V
I
LX
= -180mA
V
IN
= 3.3V
V
IN
=2.6V
Internal Low-Side
MOSFET On-Resistance
LX_ Current-Sense
Transresistance
LX_ Current-Limit
Threshold
LX_ Leakage Current
LX_ Switching Frequency
LX_ Maximum Duty Cycle
LX_ Minimum Duty Cycle
POR
POR
Thresholds
POR
Delay Time (T
D
)
POR
Output Current, High
POR
Output Voltage, Low
POR
Startup Voltage
Percentage of V
OUT
,
V
IN
= 2.6V to 5.5V
MAX1970
MAX1971/MAX1972
V
POR
= V
IN
= 5.5V, V
FB1
= V
FB2
= 1.15V
V
FB1
= 1.05V or V
FB2
= 1.05V or RSI = IN (MAX1971 only),
I
POR
= 1mA
FB1 = FB2 = GND, I
POR
= 100µA, V
IN
= 1.2V
V
OUT
rising
V
OUT
falling
87
13.3
140
-1
0.01
0.01
92
90
16.6
175
20
210
1
0.05
0.05
94
%
ms
µA
V
V
V
IN
= 2.6V to 5.5V
MAX1970/MAX1972
MAX1971
Duty Cycle = 100%,
V
IN
= 2.6V to 5.5V
V
IN
= 5.5V
V
IN
= 2.6V to 5.5V
High side
Low side
V
LX1
= V
LX2
= 5.5V
V
LX1
= V
LX2
= 0
MAX1970/MAX1972
MAX1971
-20
1.2
0.60
1.4
0.70
100
15
10
20
15
1.6
0.80
V
IN
= 5.0V
I
LX
= 180mA
V
IN
= 3.3V
V
IN
= 2.6V
0.4
0.80
-1.6
0.20
0.24
0.28
0.12
0.14
0.16
0.5
1.2
-0.85
0.6
1.60
-0.40
20
V/A
A
µA
MHz
%
%
0.23
0.25
Ω
0.32
0.37
Ω
FB1 = COMP1,
V
COMP1
= 1.2V
FB2 = COMP2,
V
COMP2
= 1.2V
FBSEL1 = unconnected
FBSEL2 = unconnected
35
35
55
55
85
85
µS
µS
CONDITIONS
MIN
TYP
MAX
UNITS
MAX1970/MAX1971/MAX1972
_______________________________________________________________________________________
3
Dual, 180° Out-of-Phase, 1.4MHz, 750mA Step-
Down Regulator with POR and RSI/PFO
MAX1970/MAX1971/MAX1972
ELECTRICAL CHARACTERISTICS (continued)
(V
IN
= V
CC
= V
EN
= 5V, R
POR
= 100kΩ to IN, R
PFO
= 100kΩ to IN, V
RSI
= 0, C
REF
= 0.1µF, FBSEL1 = unconnected, FBSEL2 =
unconnected,
T
A
= 0°C to +85°C,
unless otherwise noted. Typical values are at T
A
= +25°C.)
PARAMETER
PFO (MAX1970 and MAX1972 Only)
PFO Trip Threshold
PFO Output Current, High
PFO Output Voltage, Low
IN = V
CC
PFO = IN
I
PFO
= 1mA, V
IN
= 4.3V
V
IL
V
IH
5
-1
-1
V
IL
V
IH
0.4
V
CC
rising
V
CC
falling
3.86
-1
0.01
0.95
1.0
10
1.6
20
1
1
4.04
3.94
1
0.05
4.12
V
µA
V
CONDITIONS
MIN
TYP
MAX
UNITS
EN AND RSI (MAX1971 Only)
Logic Input Thresholds
RSI Input Resistance
EN Logic Input Current
IN = 2.6V to 5.5V
V
kΩ
µA
Internal pullup resistor to IN
Logic input at 0 or
5.5V, V
IN
= 5.5V
ELECTRICAL CHARACTERISTICS
(V
IN
= V
CC
= V
EN
= 5V, V
FB1
= V
FB2
= 1.15V, R
POR
= 100kΩ to IN, R
PFO
= 100kΩ to IN, RSI = 0, C
VCC
= 0.1µF, C
REF
= 0.1µF,
FBSEL1 = unconnected, FBSEL2 = unconnected,
T
A
= -40°C to +85°C.)
(Note 2)
PARAMETER
IN AND V
CC
IN Voltage Range
IN Supply Current
IN Shutdown Current
V
CC
Undervoltage
Lockout Threshold
REF
REF Voltage
REF Shutdown Resistance
REF Soft-Start Current
FB1 AND FB2
FB_ Regulation Voltage
OUT_ Voltage Range
OUT1 Regulation Voltage
OUT2 Regulation Voltage
Maximum Output Current
FBSEL_ = unconnected, OUT1 = FB1, OUT2 = FB2,
V
COMP_
= 1.20V to 1.80V, V
IN
= 2.6V to 5.5V
FBSEL_ = unconnected
V
IN
= 2.6V to 5.5V
V
IN
= 4.5V to 5.5V
V
IN
= 2.6V to 5.5V
V
COMP1
= 1.2V, FBSEL1= GND
V
COMP1
= 1.2V, FBSEL1 = V
CC
V
COMP2
= 1.2V, FBSEL2 = GND
V
COMP2
= 1.2V, FBSEL2 = V
CC
1.185
1.2
1.778
3.259
1.481
2.469
750
1.212
V
IN
1.818
3.333
1.515
2.525
V
V
V
V
mA
I
REF
= 0, V
IN
= 2.6V to 5.5V
REF to GND, V
EN
=0
V
REF
= 1V
20
1.185
1.212
25
30
V
Ω
µA
Switching with no load
V
IN
= 3.3V
V
IN
= 5.5V, V
EN
= 0
V
CC
rising
V
CC
falling
2.20
MAX1971
MAX1970/MAX1972
MAX1970/MAX1972
MAX1971
2.6
5.5
10
20
20
100
2.55
V
mA
µA
V
CONDITIONS
MIN
TYP
MAX
UNITS
Guaranteed by design (Note 1)
4
_______________________________________________________________________________________
Dual, 180° Out-of-Phase, 1.4MHz, 750mA Step-
Down Regulator with POR and RSI/PFO
ELECTRICAL CHARACTERISTICS (continued)
(V
IN
= V
CC
= V
EN
= 5V, V
FB1
= V
FB2
= 1.15V, R
POR
= 100kΩ to IN, R
PFO
= 100kΩ to IN, RSI = 0, C
VCC
= 0.1µF, C
REF
= 0.1µF,
FBSEL1 = unconnected, FBSEL2 = unconnected,
T
A
= -40°C to +85°C.)
(Note 2)
PARAMETER
FB1 Input Resistance
FB2 Input Resistance
FB_ Input Bias Current
COMP1 AND COMP2
COMP1
Transconductance
COMP2
Transconductance
LX1 AND LX2
Internal High-Side
MOSFET On-Resistance
Internal Low-Side
MOSFET On-Resistance
LX_ Current-Sense
Transresistance
LX_ Current-Limit
Threshold
LX_ Leakage Current
LX_ Switching Frequency
LX_ Minimum Duty Cycle
POR
POR
Thresholds
POR
Delay Time (T
D
)
POR
Output Current, High
POR
Output Voltage, Low
POR
Start-Up Voltage
Percentage of V
OUT
,
V
IN
= 2.6V to 5.5V
MAX1970
MAX1971/MAX1972
V
POR
= V
IN
= 5.5V, V
FB1
= V
FB2
= 1.15V
V
FB1
= 1.05V or V
FB2
= 1.05V or RSI = IN (MAX1971 only),
I
POR
= 1mA
FB1 = FB2 = GND, I
POR
= 100µA, V
IN
= 1.2V
V
OUT
rising
V
OUT
falling
87
13.3
140
-1
20
210
1
0.05
0.05
94
%
ms
µA
V
V
Duty cycle = 100%,
V
IN
= 2.6V to 5.5V
V
IN
= 5.5V
V
IN
= 2.6V to 5.5V
V
IN
= 2.6V to 5.5V
High side
Low side
V
LX1
= V
LX2
= 5.5V
V
LX1
= V
LX2
= 0
MAX1970/MAX1972
MAX1971
MAX1970/MAX1972
MAX1971
-20
1.2
0.60
1.6
0.80
20
15
I
LX
= -180mA
I
LX
= 180mA
V
IN
= 5.0V
V
IN
= 3.3V
V
IN
= 5.0V
V
IN
= 3.3V
0.4
0.76
-1.6
0.32
0.37
0.23
0.25
0.6
1.60
-0.40
20
Ω
Ω
V/A
A
µA
MHz
%
FB1 = COMP1,
V
COMP1
= 1.2V
FB2 = COMP2,
V
COMP2
= 1.2V
FBSEL1 = unconnected
FBSEL2 = unconnected
35
35
85
85
µS
µS
Measured from FB1 to
GND
Measured from FB2 to
GND
CONDITIONS
FBSEL1 = GND
FBSEL1 = V
CC
FBSEL2 = GND
FBSEL2 = V
CC
MIN
30
30
22.5
22.5
TYP
MAX
120
120
90
90
0.1
UNITS
kΩ
kΩ
µA
MAX1970/MAX1971/MAX1972
FB1 or FB2, FBSEL_ = unconnected, V
FB1
= V
FB2
= 1.15V
_______________________________________________________________________________________
5
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