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 MAX package.
________________________Applications
Automotive Electronics
Telecom Systems
Wall-Cube-Powered Devices
Industrial Control Systems
Firewire/IEEE1394
____________________________Features
o High-Voltage Operation (up to 36V IN)
o Efficiency >90%
o Output Power Capability Exceeds 50W
o 10-Pin Max Package
o Low-Dropout Voltage
o 100% (max) Duty Cycle
o 90A Quiescent Current
o 4A Shutdown Current
o Up to 330kHz Switching Frequency
o Output Voltage
5V or 3.3V (MAX1744)
Adjustable 1.25V to 18V (MAX1745)
o Current-Limited Control Scheme
MAX1744/MAX1745
High-Voltage, Step-Down DC-DC
Controller in MAX
________________________________________________________________ Maxim Integrated Products
1
19-1776; Rev 1; 10/01
Ordering Information
PART
TEMP RANGE
PIN-PACKAGE
MAX1744EUB
-40
C to +85C
10 MAX
MAX1744AUB
-40
C to +125C
10 MAX
MAX1745EUB
-40
C to +85C
10 MAX
MAX1745AUB
-40
C to +125C
10 MAX
GND
OUT
REF
VL
CS
MAX1744
3/5
5V
3.3V
ON
OFF
SHDN
IN
VH
EXT
P
IN
4.5V TO 36V
OUT
3.3V
OR 5V
Typical Operating Circuit
1
2
3
4
5
10
9
8
7
6
IN
EXT
VH
3/5 (FB)
( ) ARE FOR MAX1745 ONLY.
REF
VL
GND
MAX1744
MAX1745
MAX
TOP VIEW
CS
OUT
SHDN
Pin Configuration
For pricing, delivery, and ordering information, please contact Maxim/Dallas Direct! at
1-888-629-4642, or visit Maxim's website at www.maxim-ic.com.
MAX1744/MAX1745
High-Voltage, Step-Down DC-DC
Controller in MAX
2
_______________________________________________________________________________________
ABSOLUTE MAXIMUM RATINGS
ELECTRICAL CHARACTERISTICS
(VIN = SHDN = 5.5V to 36V, 3/5 = GND, ILOAD = 0, TA = 0C to +85C, unless otherwise noted. Typical values at VIN = SHDN =
36V, TA = +25C.)
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.
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 (T
A
= +70C)
10-Pin MAX (derate 5.6mW/C above 70C) .............444mW
Operating Temperature Range
MAX174_EUB ..................................................-40C to +85C
MAX174_AUB ................................................-40C to +125C
Junction Temperature ......................................................+150C
Storage Temperature Range .............................-65C to +150C
Lead Temperature (soldering, 10s) ................................+300C
PARAMETER
CONDITIONS
MIN
TYP
MAX
UNITS
Input Voltage Range
4.5
36
V
Supply Current into IN
SHDN = V
IN
= 5.5V to 36V
90
140
A
Shutdown Supply Current
SHDN = GND
4
12
A
3/5 = VL
4.85
5.00
5.15
Output Voltage (MAX1744)
3/5 = GND
3.20
3.30
3.40
V
OUT Input Current (MAX1744)
3/5 = VL, V
OUT
= 5V
28
44
A
FB Threshold Voltage (MAX1745)
Falling edge, hysteresis = 8mV
1.22
1.25
1.28
V
FB Input Current (MAX1745)
-50
50
nA
VH Output Voltage with Respect to IN
V
IN
= 5.5V to 36V, I
VH
= 100A to 20mA
-6.0
-5.3
-4.3
V
VL Output Voltage
V
IN
= 5.5V to 36V, I
VL
= 100A to 2mA
4.5
5.0
5.5
V
VL Undervoltage Lockout
2.0
3.0
4.1
V
V
CS
= V
OUT
= 2.5V to 18V
85
100
115
CS Threshold Voltage
V
CS
= V
OUT
= GND
80
110
150
mV
V
CS
= V
OUT
= 2.5V to 18V
0
15
25
CS Input Current
V
CS
= V
OUT
= GND
-25
0
A
SHDN, 3/5 Logic-High Threshold
V
IN
= 4.5V to 36V
2.4
V
SHDN, 3/5 Logic-Low Threshold
V
IN
= 4.5V to 36V
0.4
V
3/5 Input Current
SHDN = GND
1
A
3/5 = GND
1
SHDN Input Current
SHDN = 36V
12
A
EXT Resistance
8
20
Minimum EXT Off-Time
1.5
2.0
2.5
s
Minimum EXT On-Time
0.7
1.0
1.5
s
Output Line Regulation
Figure 1, 5.5V < V
IN
< 36V, I
LOAD
= 1A
5
mV/V
Output Load Regulation
Figure 1, V
IN
= 12V, 30mA < I
LOAD
< 2A
15
mV/A
Reference Voltage
I
REF
= 0
1.22
1.25
1.28
V
REF Load Regulation
0
I
REF
100A
4
10
mV
REF Line Regulation
V
IN
= 4.5V to 36V, I
REF
= 0
30
60
V/V
MAX1744/MAX1745
High-Voltage, Step-Down DC-DC
Controller in MAX
_______________________________________________________________________________________
3
ELECTRICAL CHARACTERISTICS
(VIN = SHDN = 5.5V to 36V, 3/5 = GND, ILOAD = 0, TA = -40C to +85C, unless otherwise noted.) (Note 1)
PARAMETER
CONDITIONS
MIN
MAX
UNITS
Input Voltage Range
4.5
36
V
Supply Current into IN
SHDN = V
IN
= 5.5V to 36V
140
A
Shutdown Supply Current
SHDN = GND
12
A
3/5 = VL
4.85
5.15
Output Voltage (MAX1744)
3/5 = GND
3.20
3.40
V
OUT Input Current (MAX1744)
3/5 = VL, V
OUT
= 5V
44
A
FB Threshold Voltage (MAX1745)
Falling edge, hysteresis = 8mV
1.22
1.28
V
FB Input Current (MAX1745)
-50
50
nA
VH Output Voltage with Respect to IN
V
IN
= 5.5V to 36V, I
VH
= 100A to 20mA
-6.0V
-4.3V
V
VL Output Voltage
V
IN
= 5.5V to 36V, I
VL
= 100A to 2mA
4.5
5.5
V
VL Undervoltage Lockout
2.0
4.1
V
V
CS
= V
OUT
= 2.5V to 18V
85
115
CS Threshold Voltage
V
CS
= V
OUT
= GND
80
150
mV
V
CS
= V
OUT
= 2.5V to 18V
0
25
CS Input Current
V
CS
= V
OUT
= GND
-25
0
A
SHDN, 3/5 Logic-High Threshold
V
IN
= 4.5V to 36V
2.4
V
SHDN, 3/5 Logic-Low Threshold
V
IN
= 4.5V to 36V
0.4
V
3/5 Input Current
SHDN = GND
1
A
3/5 = GND
1
SHDN Input Current
SHDN = 36V
12
A
EXT Resistance
20
Minimum EXT Off-Time
1.5
2.5
s
Minimum EXT On-Time
0.7
1.5
s
Reference Voltage
I
REF
= 0
1.22
1.28
V
REF Load Regulation
0
I
REF
100A
10
mV
REF Line Regulation
V
IN
= 4.5V to 36V, I
REF
= 0
60
V/V
MAX1744/MAX1745
High-Voltage, Step-Down DC-DC
Controller in MAX
4
_______________________________________________________________________________________
ELECTRICAL CHARACTERISTICS
(VIN = SHDN = 5.5V to 36V, 3/5 = GND, ILOAD = 0, TA = -40C to +125C, unless otherwise noted.) (Note 1)
PARAMETER
CONDITIONS
MIN
MAX
UNITS
Input Voltage Range
4.5
36
V
Supply Current into IN
SHDN = V
IN
= 5.5V to 36V
140
A
Shutdown Supply Current
SHDN = GND
15
A
3/5 = VL
4.85
5.15
Output Voltage (MAX1744)
3/5 = GND
3.20
3.40
V
OUT Input Current (MAX1744)
3/5 = VL, V
OUT
= 5V
44
A
FB Threshold Voltage (MAX1745)
Falling edge, hysteresis = 8mV
1.22
1.28
V
FB Input Current (MAX1745)
-50
50
nA
VH Output Voltage with Respect to IN
V
IN
= 5.5V to 36V, I
VH
= 100A to 20mA
-6.0V
-4.3V
V
VL Output Voltage
V
IN
= 5.5V to 36V, I
VL
= 100A to 2mA
4.5
5.5
V
VL Undervoltage Lockout
1.6
4.1
V
V
CS
= V
OUT
= 2.5V to 18V
85
115
CS Threshold Voltage
V
CS
= V
OUT
= GND
80
150
mV
V
CS
= V
OUT
= 2.5V to 18V
0
25
CS Input Current
V
CS
= V
OUT
= GND
-25
0
A
SHDN, 3/5 Logic-High Threshold
V
IN
= 4.5V to 36V
2.4
V
SHDN, 3/5 Logic-Low Threshold
V
IN
= 4.5V to 36V
0.4
V
3/5 Input Current
SHDN = GND
1
A
3/5 = GND
1
SHDN Input Current
SHDN = 36V
12
A
EXT Resistance
20
Minimum EXT Off-Time
1.5
2.5
s
Minimum EXT On-Time
0.7
1.5
s
Reference Voltage
I
REF
= 0
1.22
1.28
V
REF Load Regulation
0
I
REF
100A
10
mV
REF Line Regulation
V
IN
= 4.5V to 36V, I
REF
= 0
80
V/V
Note 1: Specifications to -40C are guaranteed by design, not production tested.
MAX1744/MAX1745
High-Voltage, Step-Down DC-DC
Controller in MAX
_______________________________________________________________________________________
5
100
0
0.0001
0.001
0.01
0.1
1
10
EFFICIENCY vs. LOAD CURRENT
(V
OUT
= +3.3V)
20
MAX1744/5toc01
LOAD CURRENT (A)
EFFICIENCY (%)
40
60
80
A: V
IN
= +5.5V
B: V
IN
= +12.0V
C: V
IN
= +24.0V
D: V
IN
= +36.0V
C
D
B
A
100
0
0.0001
0.001
0.01
0.1
1
10
EFFICIENCY vs. LOAD CURRENT
(V
OUT
= +5.0V)
20
MAX1744/5toc02
LOAD CURRENT (A)
EFFICIENCY
(%)
40
60
80
A: V
IN
= +7.2V
B: V
IN
= +12.0V
C: V
IN
= +24.0V
D: V
IN
= +36.0V
B
A
D
C
80
85
90
95
100
105
110
0
10
20
30
40
IN PIN QUIESCENT CURRENT
vs. INPUT VOLTAGE (5.5V TO 36V)
MAX1744/5toc03
INPUT VOLTAGE (V)
QUIESCENT CURRENT (
A)
0
1
4
5
6
3.5
4.5
5.5
IN PIN QUIESCENT CURRENT
vs. INPUT VOLTAGE (3.5V TO 5.5V)
MAX1744/5toc04
INPUT VOLTAGE (V)
QUIESCENT CURRENT (mA)
2
3
V
OUT
= 3.3V
0
60
40
20
80
120
100
140
0
10
20
30
40
SWITCHING FREQUENCY
vs. INPUT VOLTAGE
MAX1744/5toc05
INPUT VOLTAGE (V)
SWITCHING FREQUENCY (kHz)
V
OUT
= 3.3V
I
OUT
= 2.0A
IN PIN QUIESCENT CURRENT
vs. TEMPERATURE
MAX1744/5toc06
TEMPERATURE (
C)
QUIESCENT CURRENT (
A)
100
75
25
50
0
-25
86
87
88
89
90
91
92
93
94
95
85
-50
125
0
40
20
60
100
80
120
0
1000
2000
3000
4000
5000
EXT RISE AND FALL TIMES
vs. CAPACITANCE
MAX1744/5toc07
CAPACITANCE (pF)
t
RISE
AND t
FALL
(ns)
V
IN
= +5V
t
FALL
t
RISE
EXT RISE AND FALL TIMES
vs. TEMPERATURE
MAX1744/5toc08
TEMPERATURE (
C)
t
RISE
AND t
FALL
(ns)
100
75
25
50
0
-25
5
10
15
20
25
30
35
40
45
50
0
-50
125
t
RISE
t
FALL
V
IN
= +5V
C
L
= 1000pF
CURRENT-SENSE TRIP LEVEL
vs. TEMPERATURE
MAX1744/5toc09
TEMPERATURE (
C)
CURRENT-SENSE TRIP LEVEL (mV)
100
75
50
25
0
-25
90
95
100
105
110
115
85
-50
125
Typical Operating Characteristics
(Circuit of Figure 1, T
A
= +25C, unless otherwise specified.)
PDF 
ZIP