MAXIM MAX1744, MAX1745 User Manual

General Description

The MAX1744/MAX1745 are step-down DC-DC con­trollers 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 exter­nal components for space-critical applications.
Operation to 100% duty cycle permits the lowest possi­ble 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-sav­ing 10-pin μMAX®package.

________________________Applications

Automotive Electronics

Telecom Systems

Wall-Cube-Powered Devices

Industrial Control Systems

Firewire

®

/IEEE®1394

____________________________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

Controllers in µMAX

________________________________________________________________

Maxim Integrated Products

1

19-1776; Rev 4; 8/09

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

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 Direct at 1-888-629-4642,
or visit Maxim's website at www.maxim-ic.com.

EVALUATION KIT

AVAILABLE

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.

+

Denotes a lead(Pb)-free/RoHS-compliant package.

/V Denotes an automotive qualified part.

IN

4.5V TO 36V

ON

OFF

5V

3.3V

IN VH

SHDN

3/5

MAX1744

VL

REF

GND

EXT

CS

OUT

P

OUT

3.3V
OR 5V

MAX1744/MAX1745

High-Voltage, Step-Down DC-DC
Controllers in µMAX

2 _______________________________________________________________________________________

ABSOLUTE MAXIMUM RATINGS

ELECTRICAL CHARACTERISTICS

(VIN= V

SHDN

= 5.5V to 36V, 3/5 = GND, I

LOAD

= 0, TA= 0°C to +85°C, unless otherwise noted. Typical values at VIN= V

SHDN

=

36V, TA= +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

Input Voltage Range 4.5 36 V

Supply Current into IN V
Shutdown Supply Current SHDN = GND 4 12 μA

Output Voltage (MAX1744)

OUT Input Current (MAX1744) 3/5 = VL, V

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 VIN = 5.5V to 36V, IVH = 100μA to 20mA -6.0 -5.3 -4.3 V

VL Output Voltage VIN = 5.5V to 36V, IVL = 100μA to 2mA 4.5 5.0 5.5 V

VL Undervoltage Lockout 2.0 3.0 4.1 V

CS Threshold Voltage

CS Input Current

SHDN, 3/5 Logic-High Threshold VIN = 4.5V to 36V 2.4 V
SHDN, 3/5 Logic-Low Threshold VIN = 4.5V to 36V 0.4 V
3/5 Input Current SHDN = GND ±1μA

SHDN Input Current

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 < VIN < 36V, I

Output Load Regulation Figure 1, VIN = 12V, 30mA < I

Reference Voltage I

REF Load Regulation 0 ≤ I

REF Line Regulation VIN = 4.5V to 36V, I

PARAMETER CONDITIONS MIN TYP MAX UNITS

= VIN = 5.5V to 36V 90 140 μA

SHDN

3/5 = VL 4.85 5.00 5.15

3/5 = GND 3.20 3.30 3.40

OUT

VCS = V

V

VCS = V

V

3/5 = GND ±1

V

OUT

= V

CS

OUT

OUT

= V

CS

OUT

= 36V 12

SHDN

= 0 1.22 1.25 1.28 V

REF

≤ 100μA 4 10 mV

REF

= 5V 28 44 μA

= 2.5V to 18V 85 100 115

= V

GND

= 2.5V to 18V 0 15 25

= V

GND

= 1A 5 mV/V

LOAD

< 2A 15 mV/A

LOAD

= 0 30 60 μV/V

REF

80 110 150

-25 0

mV

μA

μA

V

MAX1744/MAX1745

High-Voltage, Step-Down DC-DC

Controllers in µMAX

_______________________________________________________________________________________ 3

ELECTRICAL CHARACTERISTICS

(VIN= V

SHDN

= 5.5V to 36V, 3/5 = GND, I

LOAD

= 0, TA= -40°C to +85°C, unless otherwise noted.) (Note 1)

Input Voltage Range 4.5 36 V

Supply Current into IN V
Shutdown Supply Current SHDN = GND 12 μA

Output Voltage (MAX1744)

OUT Input Current (MAX1744) 3/5 = VL, V

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 VIN = 5.5V to 36V, IVH = 100μA to 20mA -6.0V -4.3V V

VL Output Voltage VIN = 5.5V to 36V, IVL = 100μA to 2mA 4.5 5.5 V

VL Undervoltage Lockout 2.0 4.1 V

CS Threshold Voltage

CS Input Current

SHDN, 3/5 Logic-High Threshold VIN = 4.5V to 36V 2.4 V
SHDN, 3/5 Logic-Low Threshold VIN = 4.5V to 36V 0.4 V
3/5 Input Current SHDN = GND ±1μA

SHDN Input Current

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 Load Regulation 0 ≤ I

REF Line Regulation VIN = 4.5V to 36V, I

PARAMETER CONDITIONS MIN MAX UNITS

= VIN = 5.5V to 36V 140 μA

SHDN

3/5 = VL 4.85 5.15

3/5 = GND 3.20 3.40

= 5V 44 μA

OUT

VCS = V

V

= V

CS

VCS = V

V

= V

CS

3/5 = GND ±1

V

SHDN

= 0 1.22 1.28 V

REF

REF

= 2.5V to 18V 85 115

OUT

= V

OUT

GND

= 2.5V to 18V 0 25

OUT

= V

OUT

GND

= 36V 12

≤ 100μA 10 mV

= 0 60 μV/V

REF

80 150

-25 0

V

mV

μA

μA

MAX1744/MAX1745

High-Voltage, Step-Down DC-DC
Controllers in µMAX

4 _______________________________________________________________________________________

ELECTRICAL CHARACTERISTICS

(VIN= V

SHDN

= 5.5V to 36V, 3/5 = GND, I

LOAD

= 0, TA= -40°C to +125°C, unless otherwise noted.) (Note 1)

Note 1: Specifications to -40°C are guaranteed by design, not production tested.

Input Voltage Range 4.5 36 V

Supply Current into IN V
Shutdown Supply Current SHDN = GND 15 μA

Output Voltage (MAX1744)

OUT Input Current (MAX1744) 3/5 = VL, V

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 VIN = 5.5V to 36V, IVH = 100μA to 20mA -6.0V -4.3V V

VL Output Voltage VIN = 5.5V to 36V, IVL = 100μA to 2mA 4.5 5.5 V

VL Undervoltage Lockout 1.6 4.1 V

CS Threshold Voltage

CS Input Current

SHDN, 3/5 Logic-High Threshold VIN = 4.5V to 36V 2.4 V
SHDN, 3/5 Logic-Low Threshold VIN = 4.5V to 36V 0.4 V
3/5 Input Current SHDN = GND ±1μA

SHDN Input Current

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 Load Regulation 0 ≤ I

REF Line Regulation VIN = 4.5V to 36V, I

PARAMETER CONDITIONS MIN MAX UNITS

= VIN = 5.5V to 36V 140 μA

SHDN

3/5 = VL 4.85 5.15

3/5 = GND 3.20 3.40

= 5V 44 μA

OUT

VCS = V

V

= V

CS

VCS = V

V

= V

CS

3/5 = GND ±1

V

SHDN

REF

= 2.5V to 18V 85 115

OUT

= V

OUT

GND

= 2.5V to 18V 0 25

OUT

= V

OUT

GND

= 36V 12

= 0 1.22 1.28 V

≤ 100μA 10 mV

REF

= 0 80 μV/V

REF

80 150

-25 0

V

mV

μA

μA

MAX1744/MAX1745

High-Voltage, Step-Down DC-DC

Controllers in µMAX

_______________________________________________________________________________________

5

EFFICIENCY

(%)

Typical Operating Characteristics

(Circuit of Figure 1, TA = +25°C, unless otherwise specified.)

EFFICIENCY vs. LOAD CURRENT

= +3.3V)

(V

A

OUT

B

C

D

LOAD CURRENT (A)

A: VIN = +5.5V
B: V
C: V
D: V

100

80

60

40

EFFICIENCY (%)

20

0

0.0001 0.001 0.01 0.1 1 10

= +12.0V

IN

= +24.0V

IN

= +36.0V

IN

100

MAX1744/5toc01

EFFICIENCY vs. LOAD CURRENT

A

80

60

40

20

0

0.0001 0.001 0.01 0.1 1 10

IN PIN QUIESCENT CURRENT

vs. INPUT VOLTAGE (3.5V TO 5.5V)

6

5

4

3

2

QUIESCENT CURRENT (mA)

1

V

= 3.3V

OUT

0

3.5 4.5 5.5
INPUT VOLTAGE (V)

140

120

MAX1744/5toc04

100

80

60

40

SWITCHING FREQUENCY (kHz)

20

0

0 10203040

= +5.0V)

(V

OUT

B

D

C

A: VIN = +7.2V
B: V

IN

C: V

IN

D: V

IN

LOAD CURRENT (A)

SWITCHING FREQUENCY

vs. INPUT VOLTAGE

V

OUT

I

OUT

INPUT VOLTAGE (V)

= +12.0V
= +24.0V
= +36.0V

= 3.3V

= 2.0A

MAX1744/5toc02

MAX1744/5toc05

IN PIN QUIESCENT CURRENT

vs. INPUT VOLTAGE (5.5V TO 36V)

110

105

100

95

90

QUIESCENT CURRENT (μA)

85

80

0 10203040

INPUT VOLTAGE (V)

IN PIN QUIESCENT CURRENT

vs. TEMPERATURE

95

94

93

92

91

90

89

88

QUIESCENT CURRENT (μA)

87

86

85

-50 125

TEMPERATURE (°C)

1007525 500-25

MAX1744/5toc03

MAX1744/5toc06

120

100

(ns)

FALL

AND t

RISE

t

80

60

40

20

0

0 1000

EXT RISE AND FALL TIMES

vs. CAPACITANCE

VIN = +5V

t

FALL

t

RISE

2000

CAPACITANCE (pF)

3000

4000 5000

MAX1744/5toc07

EXT RISE AND FALL TIMES

vs. TEMPERATURE

50

VIN = +5V

45

= 1000pF

C

L

40

35

(ns)

30

FALL

25

AND t

20

RISE

t

15

10

5

0

-50 125

t

RISE

t

FALL

TEMPERATURE (°C)

CURRENT-SENSE TRIP LEVEL

vs. TEMPERATURE

115

110

MAX1744/5toc08

105

100

95

CURRENT-SENSE TRIP LEVEL (mV)

90

1007525 500-25

85

-50 125

TEMPERATURE (°C)

MAX1744/5toc09

1007550250-25