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19-1776; Rev 4; 8/09
EVAALVUAAILTAIOBNLEKIT
High-Voltage, Step-Down DC-DC
Controllers in µMAX
General Description
The MAX1744/MAX1745 are step-down DC-DC con-
trollers capable of handling up to 36V inputs. These
parts use a proprietary current-limited control scheme
for excellent light- and full-load efficiency, while their
330kHz (max) switching frequency permits small exter-
nal components for space-critical applications.
Operation to 100% duty cycle permits the lowest possi-
ble dropout voltage.
The MAX1744 contains an internal feedback network
that provides a pin-selectable output voltage of either
3.3V or 5V. The MAX1745 uses an external feedback
network to generate an adjustable output voltage
between 1.25V and 18V.
The MAX1744/MAX1745 are available in a space-sav-
ing 10-pin μMAX® package.
________________________Applications
Automotive Electronics
Telecom Systems
Wall-Cube-Powered Devices
Industrial Control Systems
Firewire®/IEEE® 1394
μMAX is a registered trademark of Maxim Integrated Products, Inc.
Firewire is a registered trademark of Apple, Inc.
IEEE is a registered service mark of the Institute of Electrical
and Electronics Engineers, Inc.
Typical Operating Circuit
____________________________Features
High-Voltage Operation (Up to 36V IN)
Efficiency > 90%
Output Power Capability Exceeds 50W
10-Pin µMax Package
Low-Dropout Voltage
100% (max) Duty Cycle
90µA Quiescent Current
4µA Shutdown Current
Up to 330kHz Switching Frequency
Output Voltage
5V or 3.3V (MAX1744)
Adjustable 1.25V to 18V (MAX1745)
Current-Limited Control Scheme
Ordering Information
PART
TEMP RANGE
PIN-PACKAGE
MAX1744EUB+
-40°C to +85°C
10 μMAX
MAX1744AUB+
-40°C to +125°C 10 μMAX
MAX1744EUB/V+ -40°C to +85°C
10 μMAX
MAX1745EUB+
-40°C to +85°C
10 μMAX
MAX1745AUB+
-40°C to +125°C 10 μMAX
MAX1745EUB/V+ -40°C to +85°C
10 μMAX
+Denotes a lead(Pb)-free/RoHS-compliant package.
/V Denotes an automotive qualified part.
Pin Configuration
IN
4.5V TO 36V
TOP VIEW
ON IN VH EXT
OFF SHDN
5V
3.3V 3/5
MAX1744
VL
REF CS
GND OUT
P
OUT
3.3V
OR 5V
+
GND 1
VL 2
REF 3
3/5 (FB) 4
MAX1744
MAX1745
OUT 5
( ) ARE FOR MAX1745 ONLY.
μMAX
10 IN
9 EXT
8 VH
7 SHDN
6 CS
________________________________________________________________ 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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High-Voltage, Step-Down DC-DC
Controllers in µMAX
ABSOLUTE MAXIMUM RATINGS
IN, EXT, SHDN to GND...........................................-0.3V to +38V
VH to GND..............................................................-0.3V to +34V
VH, EXT to IN............................................................-7V to +0.3V
CS, OUT to GND ....................................................-0.3V to +20V
FB, 3/5, REF to GND .....................................-0.3V to (VL + 0.3V)
VL to GND...................................................................-0.3V to 6V
Continuous Power Dissipation (TA = +70°C)
10-Pin μMAX (derate 5.6mW/°C above 70°C) .............444mW
Operating Temperature Range
MAX174_EUB ..................................................-40°C to +85°C
MAX174_AUB ................................................-40°C to +125°C
Junction Temperature ......................................................+150°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 = VSHDN = 5.5V to 36V, 3/5 = GND, ILOAD = 0, TA = 0°C to +85°C, unless otherwise noted. Typical values at VIN = VSHDN =
36V, TA = +25°C.)
PARAMETER
CONDITIONS
MIN TYP MAX UNITS
Input Voltage Range
4.5 36 V
Supply Current into IN
Shutdown Supply Current
VSHDN = VIN = 5.5V to 36V
SHDN = GND
90 140 μA
4 12 μA
Output Voltage (MAX1744)
3/5 = VL
3/5 = GND
4.85 5.00 5.15
3.20 3.30 3.40
V
OUT Input Current (MAX1744)
FB Threshold Voltage (MAX1745)
3/5 = VL, VOUT = 5V
Falling edge, hysteresis = 8mV
28 44
1.22 1.25 1.28
μA
V
FB Input Current (MAX1745)
VH Output Voltage with Respect to IN
VL Output Voltage
VL Undervoltage Lockout
VIN = 5.5V to 36V, IVH = 100μA to 20mA
VIN = 5.5V to 36V, IVL = 100μA to 2mA
-50 50
-6.0 -5.3 -4.3
4.5 5.0 5.5
2.0 3.0 4.1
nA
V
V
V
CS Threshold Voltage
CS Input Current
SHDN, 3/5 Logic-High Threshold
SHDN, 3/5 Logic-Low Threshold
3/5 Input Current
VCS = VOUT = 2.5V to 18V
VCS = VOUT = VGND
VCS = VOUT = 2.5V to 18V
VCS = VOUT = VGND
VIN = 4.5V to 36V
VIN = 4.5V to 36V
SHDN = GND
85 100 115
mV
80 110 150
0 15 25
μA
-25 0
2.4 V
0.4 V
±1 μA
SHDN Input Current
EXT Resistance
3/5 = GND
VSHDN = 36V
±1
μA
12
8 20 Ω
Minimum EXT Off-Time
Minimum EXT On-Time
1.5 2.0 2.5
0.7 1.0 1.5
μs
μs
Output Line Regulation
Output Load Regulation
Reference Voltage
REF Load Regulation
REF Line Regulation
Figure 1, 5.5V < VIN < 36V, ILOAD = 1A
Figure 1, VIN = 12V, 30mA < ILOAD < 2A
IREF = 0
0 IREF 100μA
VIN = 4.5V to 36V, IREF = 0
5 mV/V
15 mV/A
1.22 1.25 1.28
V
4 10 mV
30 60 μV/V
2 _______________________________________________________________________________________

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High-Voltage, Step-Down DC-DC
Controllers in µMAX
ELECTRICAL CHARACTERISTICS
(VIN = VSHDN = 5.5V to 36V, 3/5 = GND, ILOAD = 0, TA = -40°C to +85°C, unless otherwise noted.) (Note 1)
PARAMETER
Input Voltage Range
Supply Current into IN
Shutdown Supply Current
Output Voltage (MAX1744)
OUT Input Current (MAX1744)
FB Threshold Voltage (MAX1745)
FB Input Current (MAX1745)
VH Output Voltage with Respect to IN
VL Output Voltage
VL Undervoltage Lockout
CS Threshold Voltage
CS Input Current
SHDN, 3/5 Logic-High Threshold
SHDN, 3/5 Logic-Low Threshold
3/5 Input Current
SHDN Input Current
EXT Resistance
Minimum EXT Off-Time
Minimum EXT On-Time
Reference Voltage
REF Load Regulation
REF Line Regulation
CONDITIONS
VSHDN = VIN = 5.5V to 36V
SHDN = GND
3/5 = VL
3/5 = GND
3/5 = VL, VOUT = 5V
Falling edge, hysteresis = 8mV
VIN = 5.5V to 36V, IVH = 100μA to 20mA
VIN = 5.5V to 36V, IVL = 100μA to 2mA
VCS = VOUT = 2.5V to 18V
VCS = VOUT = VGND
VCS = VOUT = 2.5V to 18V
VCS = VOUT = VGND
VIN = 4.5V to 36V
VIN = 4.5V to 36V
SHDN = GND
3/5 = GND
VSHDN = 36V
IREF = 0
0 IREF 100μA
VIN = 4.5V to 36V, IREF = 0
MIN
4.5
4.85
3.20
1.22
-50
-6.0V
4.5
2.0
85
80
0
-25
2.4
1.5
0.7
1.22
MAX
36
140
12
5.15
3.40
44
1.28
50
-4.3V
5.5
4.1
115
150
25
0
0.4
±1
±1
12
20
2.5
1.5
1.28
10
60
UNITS
V
μA
μA
V
μA
V
nA
V
V
V
mV
μA
V
V
μA
μA
Ω
μs
μs
V
mV
μV/V
_______________________________________________________________________________________ 3

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High-Voltage, Step-Down DC-DC
Controllers in µMAX
ELECTRICAL CHARACTERISTICS
(VIN = VSHDN = 5.5V to 36V, 3/5 = GND, ILOAD = 0, TA = -40°C to +125°C, unless otherwise noted.) (Note 1)
PARAMETER
Input Voltage Range
Supply Current into IN
Shutdown Supply Current
Output Voltage (MAX1744)
OUT Input Current (MAX1744)
FB Threshold Voltage (MAX1745)
FB Input Current (MAX1745)
VH Output Voltage with Respect to IN
VL Output Voltage
VL Undervoltage Lockout
CS Threshold Voltage
CS Input Current
SHDN, 3/5 Logic-High Threshold
SHDN, 3/5 Logic-Low Threshold
3/5 Input Current
SHDN Input Current
EXT Resistance
Minimum EXT Off-Time
Minimum EXT On-Time
Reference Voltage
REF Load Regulation
REF Line Regulation
CONDITIONS
VSHDN = VIN = 5.5V to 36V
SHDN = GND
3/5 = VL
3/5 = GND
3/5 = VL, VOUT = 5V
Falling edge, hysteresis = 8mV
VIN = 5.5V to 36V, IVH = 100μA to 20mA
VIN = 5.5V to 36V, IVL = 100μA to 2mA
VCS = VOUT = 2.5V to 18V
VCS = VOUT = VGND
VCS = VOUT = 2.5V to 18V
VCS = VOUT = VGND
VIN = 4.5V to 36V
VIN = 4.5V to 36V
SHDN = GND
3/5 = GND
VSHDN = 36V
IREF = 0
0 IREF 100μA
VIN = 4.5V to 36V, IREF = 0
MIN
4.5
4.85
3.20
1.22
-50
-6.0V
4.5
1.6
85
80
0
-25
2.4
1.5
0.7
1.22
Note 1: Specifications to -40°C are guaranteed by design, not production tested.
MAX
36
140
15
5.15
3.40
44
1.28
50
-4.3V
5.5
4.1
115
150
25
0
0.4
±1
±1
12
20
2.5
1.5
1.28
10
80
UNITS
V
μA
μA
V
μA
V
nA
V
V
V
mV
μA
V
V
μA
μA
Ω
μs
μs
V
mV
μV/V
4 _______________________________________________________________________________________

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High-Voltage, Step-Down DC-DC
Controllers in µMAX
(Circuit of Figure 1, TA = +25°C, unless otherwise specified.)
Typical Operating Characteristics
EFFICIENCY vs. LOAD CURRENT
(VOUT = +3.3V)
100
B
A
80
60 C D
40
20
0
0.0001 0.001 0.01
A: VIN = +5.5V
B: VIN = +12.0V
C: VIN = +24.0V
D: VIN = +36.0V
0.1 1 10
LOAD CURRENT (A)
IN PIN QUIESCENT CURRENT
vs. INPUT VOLTAGE (3.5V TO 5.5V)
6
5
4
3
2
1
VOUT = 3.3V
0
3.5
4.5
INPUT VOLTAGE (V)
5.5
EFFICIENCY vs. LOAD CURRENT
(VOUT = +5.0V)
100
B
A
80
CD
60
40
20
0
0.0001
140
A: VIN = +7.2V
B: VIN = +12.0V
C: VIN = +24.0V
D: VIN = +36.0V
0.001 0.01 0.1
1
LOAD CURRENT (A)
SWITCHING FREQUENCY
vs. INPUT VOLTAGE
10
120
100
80
60
40
20
0
0
VOUT = 3.3V
IOUT = 2.0A
10 20 30
INPUT VOLTAGE (V)
40
IN PIN QUIESCENT CURRENT
vs. INPUT VOLTAGE (5.5V TO 36V)
110
105
100
95
90
85
80
0
95
94
93
92
91
90
89
88
87
86
85
-50
10 20 30
INPUT VOLTAGE (V)
IN PIN QUIESCENT CURRENT
vs. TEMPERATURE
-25 0 25 50 75 100
TEMPERATURE (°C)
40
125
EXT RISE AND FALL TIMES
vs. CAPACITANCE
120
VIN = +5V
100
80
60
tFALL
40
20
0
0
tRISE
1000 2000 3000 4000
CAPACITANCE (pF)
5000
EXT RISE AND FALL TIMES
vs. TEMPERATURE
50
45
VIN = +5V
CL = 1000pF
40 tRISE
35
30
25 tFALL
20
15
10
5
0
-50 -25
0 25 50 75 100 125
TEMPERATURE (°C)
CURRENT-SENSE TRIP LEVEL
vs. TEMPERATURE
115
110
105
100
95
90
85
-50 -25
0 25 50 75 100 125
TEMPERATURE (°C)
_______________________________________________________________________________________ 5