Rainbow Electronics MAX747 User Manual

19-0171; Rev 1; 9/93

High-Efficiency PWM, Step-Down

P-Channel DC-DC Controller

_______________General Description

The MAX747 high-efficiency, high-current, step-down controller drives external P-channel FETs. It provides 90% to 95% efficiency from a 6V supply with load currents ranging from 50mA up to 2.5A. It uses a pulse-width-modulating (PWM) current-mode control scheme to provide precise output regulation and low output noise. The MAX747’s 4V to 15V input voltage range, a fixed 5V/adjustable (Dual-Mode™) output, and a current limit set with an external resistor make this device ideal for a wide range of applications.

High efficiency is maintained with light loads due to a proprietary dual-control (Idle-Mode™) scheme that minimizes switching losses by reducing the switching frequency at light loads. The low 800µA quiescent current and ultra-low 0.6µA shutdown current further extend battery life.

External components are protected by the MAX747’s cycle-by-cycle current limit. The MAX747 also features a 2V ±1.5% reference, a comparator for low-battery detection or level translating, as well as soft-start and shutdown capability.

The MAX746, discussed in a separate data sheet, functions similarly to the MAX747, but it drives N-channel logic level FETs on the high side.

________________________Applications

Notebook Power Supplies Personal Digital Assistants Battery-Operated Equipment Cellular Phones 5V to 3.3V Green PC Applications

__________________Pin Configuration

TOP VIEW

LBI

REF

SHDN

AV+

1 2

MAX747

3 4

6 7

LBO

GND

13 12

V+ EXT

AGND

OUT

____________________________Features

♦ 90% to 95% Efficiency for 50mA to 2.5A

Output Currents

♦ 4V to 15V Input Voltage Range ♦ Low 800µA Supply Current ♦ 0.6µA Shutdown Current ♦ Drives External P-Channel FETs ♦ Cycle-by-Cycle Current Limiting ♦ 2V ±1.5% Accurate Reference Output ♦ Adjustable Soft-Start ♦ Precision Comparator for Power-Fail or

Low-Battery Warning

______________Ordering Information

PART TEMP. RANGE PIN-PACKAGE

MAX747CPD 0°C to +70°C 14 Plastic DIP MAX747CSD 0°C to +70°C 14 Narrow SO MAX747C/D 0°C to +70°C Dice* MAX747EPD -40°C to +85°C 14 Plastic DIP MAX747ESD -40°C to +85°C 14 Narrow SO MAX747MJD -55°C to +125°C 14 CERIDIP

* Contact factory for dice specifications.

__________Typical Operating Circuit

INPUT

6V TO 15V

V+

100µF

LOW-BATTERY

DETECTOR

INPUT

ON/OFF

MAX747

SHDN

LBI

REF

AV+

5OmΩ

EXT

OUT

LBO

GND

AGNDFBCCSS

0.1µF

LOW-BATTERY DETECTOR OUTPUT

5OµH

OUTPUT

5V

2.3A

430µF

MAX747

DIP/SO

™ Dual-Mode and Idle-Mode are trademarks of Maxim Integrated Products.

________________________________________________________________

Maxim Integrated Products

Call toll free 1-800-998-8800 for free samples or literature.

High-Efficiency PWM, Step-Down P-Channel DC-DC Controller

ABSOLUTE MAXIMUM RATINGS

Supply Voltage V+, AV+ to GND..............................-0.3V to 17V

AGND to GND..........................................................-0.3V to 0.3V

All Other Pins................................................-0.3V to (V+ + 0.3V)

Reference Current (I Continuous Power Dissipation (T

Plastic DIP (derate 10.00mW/°C above +70°C) ..........800mW

SO (derate 8.33mW/°C above +70°C).........................667mW

MAX747

CERDIP (derate 9.09mW/°C above +70°C).................727mW

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.

) ....................................................±2mA

REF

= +70°C)

ELECTRICAL CHARACTERISTICS

(V+ = 10V, I

Input Voltage Range V+ For regulated outputs 415V Output Voltage V

Feedback Voltage

Line Regulation Load Regulation 0V < V+ - CS < 0.125V 1.3 2.5 %

Efficiency Circuit of Figure 1, I OUT Leakage Current V FB Input Logic Low For dual-mode switchover 40 mV FB Input Leakage Current FB = 2V 0.1 100 nA

Reference Voltage I Reference Load Regulation I

Soft-Start Source Current SS = 0V 1 µA Soft-Start Fault Current SS = 2V 100 500 µA

Supply Current

Oscillator Frequency f Maximum Duty Cycle V+ = 6V 91 96 %

CS Amp I EXT Output High I EXT Output Low I EXT Sink Current V EXT Source Current V CC Impedance 24 kΩ

LBI Threshold Voltage V LBO Output Voltage Low I

LBI Input Leakage Current LBI = 2.5V 100 nA LBO Output Leakage Current V+ = 15V, LBO = 15V, LBI = 2.5V 1 µA SHDN Input Voltage Low V SHDN Input Voltage High V SHDN Input Leakage Current SHDN = 10V 0.1 100 nA

2 _______________________________________________________________________________________

= 0mA, I

LOAD

PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS

Threshold V

LIM

= 0mA, TA= T

REF

to T

, unless otherwise noted.)

MAX

V+ = 6V to 15V, 0V < V+ - CS < 0.125V, FB = 0V (includes line and load regulation) V+ - CS = 0V, external feedback mode V+ = 6V to 15V, FB = 0V 0.05 V+ = 4V to 15V, external feedback mode 0.1

= 5V 50 80 µA

OUT

= 0µA

REF

= 0µA to 100µA 920mV

REF

Operating, V+ = 15V 0.95 1.3 Operating, V+ = 10V 0.8 Shutdown mode 0.6 20 µA MAX747C 85 100 115 MAX747E/M 80 100 120

V+ - CS 125 150 175 mV

= -1mA (sourcing) V+ – 0.1 V

EXT

= 1mA (sinking) 0.25 V

EXT

= 7.5V 110 mA

EXT

= 2.5V 170 mA

EXT

LBI falling

= 0.5mA 0.4 V

SINK

OUT

REF

OSC

LIMIT

MIN

Operating Temperature Ranges:

MAX747C_D .......................................................0°C to +70°C

MAX747E_D.....................................................-40°C to +85°C

MAX747MJD..................................................-55°C to +125°C

Junction Temperature

MAX747C_D/E_D.........................................................+150°C

MAX747MJD ...............................................................+175°C

Storage Temperature Range.............................-65°C to +160°C

Lead Temperature (soldering, 10sec).............................+300°C

4.85 5.08 5.25 V

MAX747C MAX747E/M 1.95 2.00 2.05

= 0.5A to 2.5A 91 %

LOAD

MAX747C MAX747E/M 1.96 2.00 2.04

MAX747C MAX747EM 1.96 2.00 2.04

1.96 2.00 2.04

1.97 2.00 2.03

0.4 V

2.0 V

kHz

High-Efficiency PWM, Step-Down

P-Channel DC-DC Controller

__________________________________________Typical Operating Characteristics

(Circuit of Figure 1, V+ = 9V, TA = +25°C, unless otherwise noted.)

SUPPLY CURRENT vs.

TEMPERATURE

SUPPLY CURRENT (mA)

-75

-50 -25 0 25 50 75 100 125

VIN = 9V V

= 5V

OUT

ENTIRE

CIRCUIT

SCHOTTKY DIODE

LEAKAGE EXCLUDED

TEMPERATURE (°C)

PEAK INDUCTOR CURRENT vs.

OUTPUT CURRENT (V

VIN = 9V

VIN = 6V

PEAK INDUCTOR CURRENT (A)

VIN = 5V

0.01 0.1 10 OUTPUT CURRENT (A)

OUT

= 3.3V)

CONTINUOUS-CONDUCTION MODE BOUNDARY

AND CORRESPONDING PEAK INDUCTOR CURRENT (V

DISCONTINUOUS CONDUCTION REGION

SUPPLY VOLTAGE (V)

PEAK

INDUCTOR

CURRENT

0.6 1.0 1.4

0.4

0.8

OUTPUT CURRENT (A)

= 3.3V

OUT

L = 33µH R

SENSE

1.0

MAX747-TOC1

0.9

0.8

0.7

SUPPLY CURRENT (mA)

0.6

100

MAX747-TOC6

EFFICIENCY (%)

= 50mΩ

CONTINUOUS CONDUCTION REGION

1.2

SUPPLY CURRENT vs.

SUPPLY VOLTAGE

71115

SUPPLY VOLTAGE (V)

EFFICIENCY vs. OUTPUT CURRENT

= 5V)

OUT

VIN = 6V

VIN = 9V

VIN = 12V

0.01 0.1 10 OUTPUT CURRENT (A)

CONTINUOUS-CONDUCTION MODE BOUNDARY

= 3.3V)

OUT

2.0 PEAK INDUCTOR CURRENT (A)

MAX747-TOC3

1.6

1.2

0.8

0.4

AND CORRESPONDING PEAK INDUCTOR CURRENT (V

SUPPLY VOLTAGE (V)

0.5

PEAK INDUCTOR CURRENT vs. OUTPUT CURRENT (V

MAX747-TOC2

VIN = 12V

VIN = 9V

PEAK INDUCTOR CURRENT (A)

0.01 0.1 10 OUTPUT CURRENT (A)

EFFICIENCY vs. OUTPUT CURRENT

100

MAX1747-TOC7

EFFICIENCY (%)

0.01 0.1 10

DISCONTINUOUS CONDUCTION REGION

= 5V

OUT

L = 50µH R

= 50mΩ

SENSE

0.7 1.3 OUTPUT CURRENT (A)

OUTPUT CURRENT (A)

PEAK INDUCTOR

CURRENT

CONTINUOUS CONDUCTION REGION

OUT

VIN = 6V

VIN = 9V

VIN = 12V

1.10.9

= 5V)

OUT

VIN = 6V

= 3.3V)

= 5V)

OUT

2.0

PEAK INDUCTOR CURRENT (A)

MAX747-TOC4

1.6

1.2

0.8

0.4

MAX747

MAX747-TOC5

MAX747-TOC8

_______________________________________________________________________________________

High-Efficiency PWM, Step-Down P-Channel DC-DC Controller

____________________________Typical Operating Characteristics (continued)

CONTINUOUS-CONDUCTION MODE WAVEFORMS

DISCONTINUOUS-CONDUCTION IDLE-MODE WAVEFORMS

MAX747-SCOPE1

MAX747

V+ = 9V, I a) EXT VOLTAGE, 10V/div b) INDUCTOR CURRENT, 1A/div c) V

MAX747-SCOPE4

I a) V+ = 6V to 12V, 5V/div b) V

= 2.5A

OUT

RIPPLE, 50mV/div

OUT

LINE-TRANSIENT RESPONSE

= 2.0A

OUT

RIPPLE, 100mV/div

OUT

5µs/div

5ms/div

MODERATE LOAD, IDLE-MODE WAVEFORMS

MAX747-SCOPE2

20µs/div

V+ = 9V, I

= 125mA

OUT

a) EXT VOLTAGE, 10V/div b) INDUCTOR CURRENT, 200mA/div

RIPPLE, 50mV/div

c) V

OUT

LOAD-TRANSIENT RESPONSE

MAX747-SCOPE5



100µs/div

V+ = 9V, C a) LOAD CURRENT, 0.1A TO 2.5A, 1A/div b) V

= 430µF

OUT

RIPPLE, 100mV/div

OUT

MAX747-SCOPE3

5µs/div

V+ = 9V, I a) EXT VOLTAGE, 5V/div b) INDUCTOR CURRENT, 0.5A/div c) V

= 560mA

OUT

RIPPLE 100mV/div

OUT

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