Rainbow Electronics MAX763A User Manual

19-0190; Rev 0; 9/93

3.3V, Step-Down,

Current-Mode PWM DC-DC Converters

__________________General Description

The MAX748A/MAX763A are 3.3V-output CMOS, stepdown switching regulators. The MAX748A accepts inputs from 3.3V to 16V and delivers up to 500mA. The MAX763A accepts inputs between 3.3V and 11V and delivers up to 500mA. Typical efficiencies are 85% to 90%. Quiescent supply current is 1.4mA (MAX763A), and only 0.2µA in shutdown.

Pulse-width-modulation (PWM) current-mode control provides precise output regulation and excellent transient responses. Output voltage accuracy is guaranteed to be ±5% over line, load, and temperature variations. Fixed-frequency switching allows easy filtering of output ripple and noise, as well as the use of small external components. A 22µH inductor works in most applications, so no magnetics design is necessary.

The MAX748A/MAX763A also feature cycle-by-cycle current limiting, overcurrent limiting, undervoltage lockout, and programmable soft-start protection. The MAX748A is available in 8-pin DIP and 16-pin wide SO packages; the MAX763A comes in 8-pin DIP and SO packages.

___________________________Applications

5V-to-3.3V Converters Cellular Phones Portable Instruments Hand-Held Computers Computer Peripherals

________________________________Features

♦ Up to 500mA Load Currents ♦ Guaranteed 159kHz to 219.5kHz Current-Mode

PWM

♦ 85% to 90% Efficiencies ♦ 1.7mA Quiescent Current (MAX748A)

1.4mA Quiescent Current (MAX763A)

♦ 0.2µA Shutdown Supply Current ♦ 22µH Preselected Inductor Value;

No Component Design Required

♦ Overcurrent, Soft-Start, and Undervoltage

Lockout Protection

♦ Cycle-by-Cycle Current Limiting ♦ 8-Pin DIP/SO Packages (MAX763A)

_________________Ordering Information

PART TEMP. RANGE PIN-PACKAGE

MAX748ACPA 0°C to +70°C 8 Plastic DIP

MAX748ACWE 0°C to +70°C 16 Wide SO MAX748AC/D 0°C to +70°C Dice* MAX748AEPA -40°C to +85°C 8 Plastic DIP MAX748AEWE -40°C to +85°C 16 Wide SO MAX748AMJA -55°C to +125°C 8 CERDIP

Ordering Information continued on last page.

* Contact factory for dice specifications.

MAX748A/MAX763A

____________Typical Operating Circuit

INPUT

3.3V TO 16V

100µF

OUTPUT

3.3V

V+

MAX748A



SHDNON/OFF

REF

OUT

GNDSS

_______________________________________________________________________

22µH

____________________Pin Configurations

TOP VIEW

SHDN

REF

MAX748A

MAX763A

Pin Configurations continued on last page.

Maxim Integrated Products

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



DIP

V+

GND

OUT

3.3V, Step-Down, Current-Mode PWM DC-DC Converters

ABSOLUTE MAXIMUM RATINGS

Pin Voltages:

V+ (MAX748A)......................................................+17V, -0.3V

V+ (MAX763A)......................................................+12V, -0.3V

LX (MAX748A) .................................(V+ - 21V) to (V+ + 0.3V)

LX (MAX763A) .................................(V+ - 12V) to (V+ + 0.3V)

OUT.................................................................................±25V

SHDN

SS, CC, Peak Switch Current (I Reference Current (I Continuous Power Dissipation (T

8-Pin Plastic DIP (derate 6.90mW/°C above +70°C)...552mW

8-Pin SO (derate 5.88mW/°C above +70°C)...............471mW

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.

..........................................-0.3V to (V+ + 0.3V)

).....................................................2.0A

)...................................................2.5mA

REF

= +70°C)

ELECTRICAL CHARACTERISTICS

(Circuit of Figure 3, V+ = 5V, I

MAX748A/MAX763A

PARAMETER CONDITIONS

Input Voltage Range 3.3 16.0 3.3 11.0 V

Output Voltage

Line Regulation 0.13 0.13 %/V Load Regulation I

= 0mA, TA= T

LOAD

C/E temp. ranges, V+ = 4.0V to 16V, 3.135 3.3 3.465 0mA < I

M temp. range, V+ = 4.0V to 16V, 3.135 3.3 3.465 0mA < I

C/E temp. ranges, V+ = 4.75V to 16V, 3.135 3.3 3.465 0mA < I

M temp. range, V+ = 4.75V to 16V, 3.135 3.3 3.465 0mA < I

C/E temp. ranges, V+ = 4.0V to 11V, 3.135 3.3 3.465 0mA < I

M temp. range, V+ = 4.0V to 11V, 3.135 3.3 3.465 0mA < I

C/E temp. ranges, V+ = 4.75V to 11V, 3.135 3.3 3.465 0mA < I

M temp. range, V+ = 4.75V to 11V, 3.135 3.3 3.465 0mA < I

LOAD

< 300mA

LOAD

< 250mA

LOAD

< 500mA

LOAD

< 400mA

LOAD

< 300mA

LOAD

< 250mA

LOAD

< 500mA

LOAD

< 400mA

LOAD

= 0mA to 500mA 0.001 0.001 %/mA

MIN

to T

, unless otherwise noted.)

MAX

16-Pin Wide SO (derate 9.52mW/°C above +70°C)....762mW

8-Pin CERDIP (derate 8.00mW/°C above +70°C).......640mW

Operating Temperature Ranges:

MAX7__AC__ ....................................................0°C to +70°C

MAX7__AE__ .................................................-40°C to +85°C

MAX7__AMJA__ ..........................................-55°C to +125°C

Junction Temperatures:

MAX7__AC/E ..............................................................+150°C

MAX7__AM.................................................................+175°C

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

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

MAX748A MAX763A

MIN TYP MAX MIN TYP MAX

UNITS

2 ________________________________________________________________________________________________

3.3V, Step-Down,

Current-Mode PWM DC-DC Converters

ELECTRICAL CHARACTERISTICS (continued)

(Circuit of Figure 3, V+ = 5V, I

PARAMETER CONDITIONS

Efficiency V+ = 5V

Supply Current Includes switch current 1.7 3.0 1.4 2.5 mA Shutdown Current

Shutdown Input Threshold

Shutdown Input Leakage Current

Short-Circuit Current 1.2 1.2 A Undervoltage Lockout V+ falling 2.7 3.0 2.7 3.0 V LX On Resistance ILX= 500mA 1.0 1.0 Ω LX Leakage Current V+ = 12V, LX = 0 10 10 nA Reference Voltage TA= +25°C 1.15 1.22 1.30 1.15 1.22 1.30 V Reference Drift TA= T Oscillator Frequency 159 180 212.5 159 200 212.5 kHz Compensation Pin

Impedance

Note 1: The standby current typically settles to 10µA (over temperature) within 2 seconds; however, to decrease test time, the part is guaranteed at a 100µA maximum value.

= 0mA, TA= T

LOAD

MIN

to T

, unless otherwise noted.)

MAX

MAX748A MAX763A

MIN TYP MAX MIN TYP MAX

= 300mA 88 88

LOAD

= 100mA 90 90

LOAD

SHDN

= 0V (Note 1) 0.2 100.0 0.2 100.0 µA

2.0 2.0

0.25 0.25

1.0 1.0 µA

MIN

to T

MAX

50 50 ppm/°C

7500 7500 Ω

UNITS

MAX748A/MAX763A

________________________________________________T ypical Operating Characteristics

(Circuit of Figure 3, TA = +25°C, V

MAXIMUM OUTPUT CURRENT

vs. SUPPLY VOLTAGE

1000

800

600

400

200

MAXIMUM OUTPUT CURRENT (mA)

MAX748A

MAX763A

0246810121416

SUPPLY VOLTAGE (V)

_________________________________________________________________________________________________

= 3.3V, unless otherwise noted.)

OUT

100

95 90

85 80 75

EFFICIENCY (%)

NOTE 2

65 60

0 100 200 300 400 500 600 700 800

EFFICIENCY vs. OUTPUT CURRENT

MAX763A

VIN = 7.0V

VIN = 5.0V

VIN = 11.0V

NOTE 2

OUTPUT CURRENT (mA)

EFFICIENCY vs. OUTPUT CURRENT

MAX748A

100

VIN = 4.5V

95 90 85 80 75

EFFICIENCY (%)

VIN = 12V

65 60

0 100 200 300 400 500 600 700 800 900

VIN = 6V

VIN = 16V

VIN = 9V

NOTE 2

OUTPUT CURRENT (mA)

3.3V, Step-Down, Current-Mode PWM DC-DC Converters

____________________________Typical Operating Characteristics (continued)

(Circuit of Figure 3, TA = +25°C, V

MAX763A 

QUIESCENT SUPPLY CURRENT

vs. SUPPLY VOLTAGE

4.5

4.0

= 0mA

OUT

3.5

3.0

2.5

2.0

1.5

1.0

QUIESCENT SUPPLY CURRENT (mA)

0.5 0

MAX748A/MAX763A

0 1 2 3 4 5 6 7 8 9 10 11 12

275 250

225 200 175

MAX763A

150

OSCILLATOR FREQUENCY (kHz)

125

100

0 2 4 6 810121416

TA = +125°C

TA = -55°C

TA = +25°C

SUPPLY VOLTAGE (V)

OSCILLATOR FREQUENCY

vs. SUPPLY VOLTAGE

MAX748A

SUPPLY VOLTAGE (V)

= 3.3V, unless otherwise noted.)

OUT

QUIESCENT SUPPLY CURRENT

5.0

4.0

3.0

2.0

1.0

QUIESCENT SUPPLY CURRENT (mA)

3.5

3.0

2.5

2.0

1.5

1.0

SHUTDOWN CURRENT (µA)

0.5

vs. SUPPLY VOLTAGE

= OmA

OUT

TA = +125°C

0 2 4 6 8 10 12 14 16

NOTES 3, 4

-60 -40 -20 0 20 40 60 80 100 120 140

MAX748A

TA = -55°C

TA = +25°C

SUPPLY VOLTAGE (V)

SHUTDOWN CURRENT

vs. TEMPERATURE

= 0mA

OUT

V+ = 5V

TEMPERATURE (°C)

PEAK INDUCTOR CURRENT

vs. OUTPUT CURRENT

1000

800

600

400

200

PEAK INDUCTOR CURRENT (mA)

4.0

3.5

3.0

2.5

2.0

1.5

OUTPUT VOLTAGE (V)

1.0

0.5

VIN = 11V

VIN = 8V

0 50 100 150 200 250 300 350 400 450 500 550

OUTPUT CURRENT (mA)

OUTPUT VOLTAGE

vs. SUPPLY VOLTAGE

= 50mA

LOAD

= 200mA

LOAD

= 300mA

LOAD

2.0 2.5 3.0 3.5 4.0 4.5 5.0 SUPPLY VOLTAGE (V)

VIN = 6V

= 500mA

OUTPUT VOLTAGE

4.0

3.5

3.0

2.5

2.0

1.5

OUTPUT VOLTAGE (V)

1.0

0.5

vs. OUTPUT CURRENT

VIN = 4.0V

VIN = 3.5V

VIN = 3.0V

0 50 100 150 200 250 300 350 400 450 500

OUTPUT CURRENT (mA)

OSCILATOR FREQUENCY (kHz)

OSCILLATOR FREQUENCY

vs. TEMPERATURE

300

= 100mA

OUT

V+ = 5V

250

200

150

100

-60 -40 -20 0 20 40 60 80 100 120 140 TEMPERATURE (°C)

MAX748A

MAX763A

4 _______________________________________________________________________________________

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