Datasheet

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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

/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

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

GND

OUT

REF

MAX1744

3/5

3.3V

OFF

SHDN

IN VH

EXT

4.5V TO 36V

OUT

3.3V

OR 5V

Typical Operating Circuit

EXT

3/5 (FB)

( ) ARE FOR MAX1745 ONLY.

REF

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.

Summary of content (15 pages)

PAGE 1
9-1776; Rev 4; 8/09 KIT ATION EVALU E L B AVAILA High-Voltage, Step-Down DC-DC Controllers in µMAX 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.
PAGE 2
MAX1744/MAX1745 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....
PAGE 3
High-Voltage, Step-Down DC-DC Controllers in µMAX (VIN = VSHDN = 5.5V to 36V, 3/5 = GND, ILOAD = 0, TA = -40°C to +85°C, unless otherwise noted.) (Note 1) PARAMETER CONDITIONS Input Voltage Range MIN MAX UNITS 4.5 36 V Supply Current into IN VSHDN = VIN = 5.5V to 36V 140 μA Shutdown Supply Current SHDN = GND 12 μA Output Voltage (MAX1744) 3/5 = VL 4.85 5.15 3/5 = GND 3.20 3.40 44 μA 1.
PAGE 4
MAX1744/MAX1745 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 CONDITIONS Input Voltage Range MIN MAX UNITS 4.5 36 V Supply Current into IN VSHDN = VIN = 5.5V to 36V 140 μA Shutdown Supply Current SHDN = GND 15 μA Output Voltage (MAX1744) 3/5 = VL 4.85 5.15 3/5 = GND 3.20 3.40 44 μA 1.
PAGE 5
High-Voltage, Step-Down DC-DC Controllers in µMAX EFFICIENCY vs. LOAD CURRENT (VOUT = +3.3V) D 40 A: VIN = +5.5V B: VIN = +12.0V C: VIN = +24.0V D: VIN = +36.0V 20 40 A: VIN = +7.2V B: VIN = +12.0V C: VIN = +24.0V D: VIN = +36.0V 20 0 0.001 0.01 0.1 1 10 0.0001 0.001 0.01 0.1 1 100 95 90 85 80 0 10 10 20 30 40 LOAD CURRENT (A) LOAD CURRENT (A) INPUT VOLTAGE (V) IN PIN QUIESCENT CURRENT vs. INPUT VOLTAGE (3.5V TO 5.5V) SWITCHING FREQUENCY vs.
PAGE 6
Typical Operating Characteristics (continued) (Circuit of Figure 1, TA = +25°C, unless otherwise specified.) REFERENCE OUTPUT VOLTAGE CHANGE vs. TEMPERATURE MAX1744 ENTERING/EXITING SHUTDOWN MAX1744/5toc11 MAX1744/5toc10 5 REFERENCE OUTPUT VOLTAGE CHANGE (%) 4 3 2 RL = 3.
PAGE 7
High-Voltage, Step-Down DC-DC Controllers in µMAX NAME PIN FUNCTION MAX1744 MAX1745 1 GND GND 2 VL VL 5V Linear Regulator Output. VL provides power to the internal circuitry and can supply up to 1mA to an external load. Bypass VL to GND with 4.7μF or greater capacitor. 3 REF REF 1.25V Reference Output. REF can supply up to 100μA to an external load. Bypass REF to GND with a 0.1μF or greater ceramic capacitor. 4 3/5 — 3.3V or 5V Selection. Connect 3/5 to GND to set the output voltage to 3.
PAGE 8
MAX1744/MAX1745 High-Voltage, Step-Down DC-DC Controllers in µMAX INPUT 4.5V TO 36V C2 4.7μF LOW ESR C3 4.7μF D2 0.47μF 5V VH IN ON OFF SHDN 3.3V 3/5 EXT MAX1744 VL P M1 FAIRCHILD NDS9407 L1 22μH CS OUT REF GND D1 NIHON EC2IQ506 RSENSE 40mΩ OUT 3.3V OR 5V 2A C1 220μF Figure 1. Typical Application Circuit 100% Duty Cycle and Dropout The MAX1744/MAX1745 operate with a duty cycle up to 100%.
PAGE 9
High-Voltage, Step-Down DC-DC Controllers in µMAX MAX1744/MAX1745 EXT IN REF VH SHDN VH LINEAR REGULATOR VL VL LINEAR REGULATOR Q 1.25 REFERENCE TRIG MINIMUM ON-TIME ONE SHOT OUT ERROR COMPARATOR Q (FB) TRIG MINIMUM OFF-TIME ONE SHOT 3/5 Q S R ( ) MAX1745 ONLY - - - MAX1744 ONLY SHDN - + CS 100mV Figure 2. Simplified Functional Diagram lower frequencies, reducing the MOSFET gate drive and switching losses.
PAGE 10
MAX1744/MAX1745 High-Voltage, Step-Down DC-DC Controllers in µMAX A A B B C C 10μs/div 10μs/div CIRCUIT OF FIGURE 1, VIN = 18V, VOUT = 3.3V, ILOAD = 100mA A: MOSFET DRAIN, 10V/div B: OUT, 50mV/div, 3.3V DC OFFSET C: INDUCTOR CURRENT, 1A/div CIRCUIT OF FIGURE 1, VIN = 18V, VOUT = 3.3V, ILOAD = 1.5A A: MOSFET DRAIN, 10V/div B: OUT, 50mV/div, 3.3V DC OFFSET C: INDUCTOR CURRENT, 1A/div Figure 3. Discontinuous-Conduction Mode, Light-Load-Current Waveform Figure 4.
PAGE 11
High-Voltage, Step-Down DC-DC Controllers in µMAX Current-Sense-Resistor Selection The current-sense comparator limits the peak switching current to VCS/RSENSE, where RSENSE is the value of the current-sense resistor and VCS is the current-sense threshold. VCS is typically 100mV. Minimizing the peak switching current will increase efficiency and reduce the size and cost of external components.
PAGE 12
MAX1744/MAX1745 High-Voltage, Step-Down DC-DC Controllers in µMAX Capacitor Selection Table 1.
PAGE 13
High-Voltage, Step-Down DC-DC Controllers in µMAX degrade performance. The current-sense resistor must be placed within 0.2 inches (5mm) of the controller IC, directly between OUT and CS. Place voltage feedback resistors (MAX1745) next to the FB pin (no more than 0.2in) rather than near the output. Place the 0.47μF input bypass capacitor within 0.2in (5mm) of IN. Refer to the MAX1744 Evaluation Kit manual for a twolayer PC board example.
PAGE 14
Package Information For the latest package outline information and land patterns, go to www.maxim-ic.com/packages. PACKAGE TYPE PACKAGE CODE DOCUMENT NO. 10 μMAX U10CN+1 21-0061 10LUMAX.EPS MAX1744/MAX1745 High-Voltage, Step-Down DC-DC Controllers in µMAX α α Note: MAX1744/MAX1745 do not feature exposed pads.
PAGE 15
High-Voltage, Step-Down DC-DC Controllers in µMAX PAGES CHANGED REVISION NUMBER REVISION DATE 0 7/00 Initial release. — 2 8/06 — — 3 4/09 Added lead-free and automotive qualified packages to Ordering Information. 4 8/09 Added MAX1744 automotive package to Ordering Information. DESCRIPTION 1–4, 10, 13 1 Maxim cannot assume responsibility for use of any circuitry other than circuitry entirely embodied in a Maxim product. No circuit patent licenses are implied.