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1745EUB.pdf
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DC-DC控制器The MAX1744/MAX1745 are step-down DC-DC controllers capable of handling up to 36V inputs.
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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/IEEE1394
____________________________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
MAX1744/MAX1745
High-Voltage, Step-Down DC-DC
Controller in µMAX
________________________________________________________________ Maxim Integrated Products 1
19-1776; Rev 1; 10/01
Ordering Information
PART TEMP RANGE PIN-PACKAGE
MAX1744EUB -40°C to +85°C 10 µMAX
MAX1744AUB
-40°C to +125°C
10 µMAX
MAX1745EUB -40°C to +85°C 10 µMAX
MAX1745AUB
-40°C to +125°C
10 µMAX
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
µMAX
TOP VIEW
CSOUT
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 µMAX
2 _______________________________________________________________________________________
ABSOLUTE MAXIMUM RATINGS
ELECTRICAL CHARACTERISTICS
(V
IN
= SHDN = 5.5V to 36V, 3/5 = GND, I
LOAD
= 0, T
A
= 0°C to +85°C, unless otherwise noted. Typical values at V
IN
= SHDN =
36V, T
A
= +25°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.
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
= +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
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 µA
Shutdown Supply Current SHDN = GND 4 12 µA
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 µA
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
= 100µA to 20mA -6.0 -5.3 -4.3 V
VL Output Voltage V
IN
= 5.5V to 36V, I
VL
= 100µA 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
µA
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 ±1µA
3/5 = GND ±1
SHDN Input Current
SHDN = 36V 12
µA
EXT Resistance 820Ω
Minimum EXT Off-Time 1.5 2.0 2.5 µs
Minimum EXT On-Time 0.7 1.0 1.5 µs
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
≤ 100µA 4 10 mV
REF Line Regulation V
IN
= 4.5V to 36V, I
REF
= 0 30 60 µV/V
MAX1744/MAX1745
High-Voltage, Step-Down DC-DC
Controller in µMAX
_______________________________________________________________________________________ 3
ELECTRICAL CHARACTERISTICS
(V
IN
= SHDN = 5.5V to 36V, 3/5 = GND, I
LOAD
= 0, T
A
= -40°C to +85°C, 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 µA
Shutdown Supply Current SHDN = GND 12 µA
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 µA
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
= 100µA to 20mA -6.0V -4.3V V
VL Output Voltage V
IN
= 5.5V to 36V, I
VL
= 100µA 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
µA
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 ±1µA
3/5 = GND ±1
SHDN Input Current
SHDN = 36V 12
µA
EXT Resistance 20 Ω
Minimum EXT Off-Time 1.5 2.5 µs
Minimum EXT On-Time 0.7 1.5 µs
Reference Voltage I
REF
= 0 1.22 1.28 V
REF Load Regulation 0 ≤ I
REF
≤ 100µA 10 mV
REF Line Regulation V
IN
= 4.5V to 36V, I
REF
= 0 60 µV/V
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