__________________General Description
The MAX748A/MAX763A are 3.3V-output CMOS, step-
down 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 0.2A in shutdown.
Pulse-width-modulation (PWM) current-mode control pro-
vides 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 22H inductor works in most applica-
tions, so no magnetics design is necessary.
The MAX748A/MAX763A also feature cycle-by-cycle cur-
rent 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
o
Up to 500mA Load Currents
o
Guaranteed 159kHz to 219.5kHz Current-Mode
PWM
o
85% to 90% Efficiencies
o
1.7mA Quiescent Current (MAX748A)
1.4mA Quiescent Current (MAX763A)
o
0.2A Shutdown Supply Current
o
22H Preselected Inductor Value;
No Component Design Required
o
Overcurrent, Soft-Start, and Undervoltage
Lockout Protection
o
Cycle-by-Cycle Current Limiting
o
8-Pin DIP/SO Packages (MAX763A)
_________________Ordering Information
PART
TEMP. RANGE
PIN-PACKAGE
MAX748A
CPA
0C to +70C
8 Plastic DIP
MAX748ACWE
0C to +70C
16 Wide SO
MAX748AC/D
0C to +70C
Dice*
MAX748AEPA
-40C to +85C
8 Plastic DIP
MAX748AEWE
-40C to +85C
16 Wide SO
MAX748AMJA
-55C to +125C
8 CERDIP
MAX748A/MAX763A
3.3V, Step-Down,
Current-Mode PWM DC-DC Converters
_______________________________________________________________________
Maxim Integrated Products
1
Call toll free 1-800-998-8800 for free samples or literature.
19-0190; Rev 0; 9/93
Ordering Information continued on last page.
* Contact factory for dice specifications.
____________________Pin Configurations
MAX748A
INPUT
3.3V TO 16V
V+
LX
OUT
CC
GND
SS
REF
SHDN
ON/OFF
22
H
OUTPUT
3.3V
100
F
____________Typical Operating Circuit
TOP VIEW
1
2
3
4
8
7
6
5
V+
LX
GND
OUT
CC
SS
REF
MAX748A
MAX763A
DIP
SHDN
Pin Configurations continued on last page.
MAX748A/MAX763A
3.3V, Step-Down,
Current-Mode PWM DC-DC Converters
2
________________________________________________________________________________________________
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.
ELECTRICAL CHARACTERISTICS
(Circuit of Figure 3, V+ = 5V, I
LOAD
= 0mA, T
A
= T
MIN
to T
MAX
, unless otherwise noted.)
PARAMETER
CONDITIONS
MAX748A
MAX763A
UNITS
MIN
TYP
MAX
MIN
TYP
MAX
Input Voltage Range
3.3
16.0
3.3
11.0
V
C/E temp. ranges,
V+ = 4.0V to 16V,
3.135
3.3
3.465
0mA < I
LOAD
< 300mA
M temp. range,
V+ = 4.0V to 16V,
3.135
3.3
3.465
0mA < I
LOAD
< 250mA
C/E temp. ranges,
V+ = 4.75V to 16V,
3.135
3.3
3.465
0mA < I
LOAD
< 500mA
M temp. range,
V+ = 4.75V to 16V,
3.135
3.3
3.465
Output Voltage
0mA < I
LOAD
< 400mA
V
C/E temp. ranges,
V+ = 4.0V to 11V,
3.135
3.3
3.465
0mA < I
LOAD
< 300mA
M temp. range,
V+ = 4.0V to 11V,
3.135
3.3
3.465
0mA < I
LOAD
< 250mA
C/E temp. ranges,
V+ = 4.75V to 11V,
3.135
3.3
3.465
0mA < I
LOAD
< 500mA
M temp. range,
V+ = 4.75V to 11V,
3.135
3.3
3.465
0mA < I
LOAD
< 400mA
Line Regulation
0.13
0.13
%/V
Load Regulation
I
LOAD
= 0mA to 500mA
0.001
0.001
%/mA
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
SS, CC,
SHDN ..........................................-0.3V to (V+ + 0.3V)
Peak Switch Current (I
LX
) .....................................................2.0A
Reference Current (I
REF
) ...................................................2.5mA
Continuous Power Dissipation (T
A
= +70C)
8-Pin Plastic DIP (derate 6.90mW/C above +70C)...552mW
8-Pin SO (derate 5.88mW/C above +70C) ...............471mW
16-Pin Wide SO (derate 9.52mW/C above +70C)....762mW
8-Pin CERDIP (derate 8.00mW/C above +70C) .......640mW
Operating Temperature Ranges:
MAX7_ _ AC_ _ ....................................................0C to +70C
MAX7_ _ AE_ _ .................................................-40C to +85C
MAX7_ _ AMJA_ _ ..........................................-55C to +125C
Junction Temperatures:
MAX7_ _ AC/E ..............................................................+150C
MAX7_ _ AM .................................................................+175C
Storage Temperature Range ............................-65C to +160C
Lead Temperature (soldering, 10sec) ............................+300C
MAX748A/MAX763A
3.3V, Step-Down,
Current-Mode PWM DC-DC Converters
_________________________________________________________________________________________________
3
Note 1:
The standby current typically settles to 10A (over temperature) within 2 seconds; however, to decrease test time, the part
is guaranteed at a 100A maximum value.
MAXIMUM OUTPUT CURRENT
vs. SUPPLY VOLTAGE
MAXIMUM OUTPUT CURRENT (mA)
0
200
400
600
800
1000
0
2
4
6
8
10
12
14
16
SUPPLY VOLTAGE (V)
MAX748A
MAX763A
NOTE 2
MAX763A
EFFICIENCY vs. OUTPUT CURRENT
EFFICIENCY (%)
60
65
70
75
80
85
90
95
100
0
100 200 300 400 500 600
700 800
OUTPUT CURRENT (mA)
VIN = 7.0V
VIN = 5.0V
VIN = 11.0V
NOTE 2
MAX748A
EFFICIENCY vs. OUTPUT CURRENT
EFFICIENCY (%)
OUTPUT CURRENT (mA)
60
65
70
75
80
85
90
95
100
0
100 200 300 400 500 600 700 800 900
VIN = 4.5V
VIN = 16V
VIN = 12V
VIN = 9V
VIN = 6V
NOTE 2
________________________________________________Typical Operating Characteristics
(Circuit of Figure 3, T
A
= +25C, V
OUT
= 3.3V, unless otherwise noted.)
PARAMETER
CONDITIONS
MAX748A
MAX763A
UNITS
MIN
TYP
MAX
MIN
TYP
MAX
Efficiency
V+ = 5V
I
LOAD
= 300mA
88
88
%
I
LOAD
= 100mA
90
90
Supply Current
Includes switch current
1.7
3.0
1.4
2.5
mA
Shutdown Current
SHDN = 0V (Note 1)
0.2
100.0
0.2
100.0
A
Shutdown Input
V
IH
2.0
2.0
V
Threshold
V
IL
0.25
0.25
Shutdown Input
1.0
1.0
A
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
I
LX
= 500mA
1.0
1.0
LX Leakage Current
V+ = 12V, LX = 0
10
10
nA
Reference Voltage
T
A
= +25C
1.15
1.22
1.30
1.15
1.22
1.30
V
Reference Drift
T
A
= T
MIN
to T
MAX
50
50
ppm/C
Oscillator Frequency
159
180
212.5
159
200
212.5
kHz
Compensation Pin
7500
7500
Impedance
ELECTRICAL CHARACTERISTICS (continued)
(Circuit of Figure 3, V+ = 5V, I
LOAD
= 0mA, T
A
= T
MIN
to T
MAX
, unless otherwise noted.)
MAX748A/MAX763A
3.3V, Step-Down,
Current-Mode PWM DC-DC Converters
4
_______________________________________________________________________________________
____________________________Typical Operating Characteristics (continued)
(Circuit of Figure 3, T
A
= +25C, V
OUT
= 3.3V, unless otherwise noted.)
MAX763A
QUIESCENT SUPPLY CURRENT
vs. SUPPLY VOLTAGE
SUPPLY VOLTAGE (V)
QUIESCENT SUPPLY CURRENT (mA)
4.5
4.0
3.5
3.0
2.5
2.0
1.5
1.0
0.5
0
0
1
2
3 4
5
6
7
8
9 10 11 12
IOUT = 0mA
TA = +125C
TA = -55C
TA = +25C
MAX748A
QUIESCENT SUPPLY CURRENT
vs. SUPPLY VOLTAGE
QUIESCENT SUPPLY CURRENT (mA)
5.0
4.0
3.0
2.0
1.0
0
SUPPLY VOLTAGE (V)
0
2
4
6
8
10
12
14
16
IOUT = OmA
TA = +125C
TA = -55C
TA = +25C
PEAK INDUCTOR CURRENT
vs. OUTPUT CURRENT
PEAK INDUCTOR CURRENT (mA)
0
200
400
600
800
1000
0 50 100 150 200 250 300 350 400 450 500 550
OUTPUT CURRENT (mA)
VIN = 11V
VIN = 6V
VIN = 8V
OSCILLATOR FREQUENCY
vs. SUPPLY VOLTAGE
OSCILLATOR FREQUENCY (kHz)
100
125
150
250
175
200
225
275
0
2
4
6
8
10
12
14
16
SUPPLY VOLTAGE (V)
MAX748A
MAX763A
OUTPUT VOLTAGE
vs. OUTPUT CURRENT
OUTPUT VOLTAGE (V)
0
0.5
1.0
1.5
2.0
2.5
3.0
3.5
4.0
0
50 100 150 200 250 300 350 400 450 500
OUTPUT CURRENT (mA)
VIN = 4.0V
VIN = 3.0V
VIN = 3.5V
SHUTDOWN CURRENT
vs. TEMPERATURE
TEMPERATURE (C)
SHUTDOWN CURRENT (
A)
3.5
3.0
2.5
2.0
1.5
1.0
0.5
0
-60 -40 -20
0
20
40 60
80 100 120 140
IOUT = 0mA
V+ = 5V
NOTES 3, 4
OUTPUT VOLTAGE
vs. SUPPLY VOLTAGE
OUTPUT VOLTAGE (V)
2.0
2.5
3.0
3.5
4.0
4.5
5.0
0
0.5
1.0
1.5
2.0
2.5
3.0
3.5
4.0
SUPPLY VOLTAGE (V)
ILOAD = 200mA
ILOAD = 50mA
ILOAD = 300mA
ILOAD = 500mA
OSCILLATOR FREQUENCY
vs. TEMPERATURE
OSCILATOR FREQUENCY (kHz)
0
50
100
150
200
250
300
-60 -40 -20
0
20
40 60 80 100 120 140
TEMPERATURE (C)
MAX748A
MAX763A
IOUT = 100mA
V+ = 5V
MAX748A/MAX763A
3.3V, Step-Down,
Current-Mode PWM DC-DC Converters
_______________________________________________________________________________________
5
_________________________________Typical Operating Characteristics (continued)
(Circuit of Figure 3, T
A
= +25C, V
OUT
= 3.3V, unless otherwise noted.)
SWITCHING WAVEFORMS,
CONTINUOUS CONDUCTION
2
s/div
A: SWITCH VOLTAGE (LX PIN), 5V/div, 0V TO +6V
B: INDUCTOR CURRENT, 200mA/div
C: OUTPUT VOLTAGE RIPPLE, 50mV/div
V+ = 6V, IOUT = 250mA
6V
0V
400mA
0mA
A
B
B
C
SWITCHING WAVEFORMS,
DISCONTINUOUS CONDUCTION
2
s/div
A: SWITCH VOLTAGE (LX PIN), 5V/div, 0V TO +6V
B: INDUCTOR CURRENT, 100mA/div
C: OUTPUT VOLTAGE RIPPLE, 50mV/div
V+ = 6V, IOUT = 75mA
6V
0V
200mA
0mA
A
C
LINE-TRANSIENT RESPONSE
5ms/div
A: VOUT, 50mV/div
B: V+, 5V/div, 7.0V TO 10.0V
IOUT = 350mA
10V
7V
0V
B
A
LOAD-TRANSIENT RESPONSE
5ms/div
A: VOUT, 50mV/div
B: IOUT, 200mA/div, 0mA TO 500mA
V+ = 6V
500mA
0mA
B
A
Note 2:
Operation beyond the specifications listed in the
Electrical Characteristics may exceed the power dissipation ratings of
the device.
Note 3:
Wide temperature range circuit of Figure 5 using Sprague surface-mount capacitors.
Note 4:
Standby current includes all external component leakage currents. Capacitor leakage currents dominate at TA = +85C.
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