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, 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 0.2µA 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 22µH 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.
________________________________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
0.2µA Shutdown Supply Current
o
22µH 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)
MAX748A/MAX763A
_________________Ordering Information
PART
MAX748ACPA
MAX748ACWE
MAX748AC/D
MAX748AEPA
MAX748AEWE
MAX748AMJA
TEMP. RANGE
0°C to +70°C
0°C to +70°C
0°C to +70°C
-40°C to +85°C
-40°C to +85°C
-55°C to +125°C
PIN-PACKAGE
8 Plastic DIP
16 Wide SO
Dice*
8 Plastic DIP
16 Wide SO
8 CERDIP
___________________________Applications
5V-to-3.3V Converters
Cellular Phones
Portable Instruments
Hand-Held Computers
Computer Peripherals
Ordering Information continued on last page.
* Contact factory for dice specifications.
____________Typical Operating Circuit
INPUT
3.3V TO 16V
V+
22µH
LX
OUTPUT
3.3V
____________________Pin Configurations
TOP VIEW
MAX748A
ON/OFF
SHDN
OUT
100µF
REF
SS
GND
CC
SHDN
1
REF
2
8
7
V+
LX
GND
OUT
SS
3
CC
4
MAX748A
MAX763A
6
5
DIP
Pin Configurations continued on last page.
_______________________________________________________________________
Maxim Integrated Products
1
Call toll free 1-800-998-8800 for free samples or literature.
3.3V, Step-Down,
Current-Mode PWM DC-DC Converters
MAX748A/MAX763A
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
= +70°C)
8-Pin Plastic DIP (derate 6.90mW/°C above +70°C)...552mW
8-Pin SO (derate 5.88mW/°C above +70°C) ...............471mW
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
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
Input Voltage Range
C/E temp. ranges,
V+ = 4.0V to 16V,
0mA < I
LOAD
< 300mA
M temp. range,
V+ = 4.0V to 16V,
0mA < I
LOAD
< 250mA
C/E temp. ranges,
V+ = 4.75V to 16V,
0mA < I
LOAD
< 500mA
M temp. range,
V+ = 4.75V to 16V,
0mA < I
LOAD
< 400mA
C/E temp. ranges,
V+ = 4.0V to 11V,
0mA < I
LOAD
< 300mA
M temp. range,
V+ = 4.0V to 11V,
0mA < I
LOAD
< 250mA
C/E temp. ranges,
V+ = 4.75V to 11V,
0mA < I
LOAD
< 500mA
M temp. range,
V+ = 4.75V to 11V,
0mA < I
LOAD
< 400mA
Line Regulation
Load Regulation
I
LOAD
= 0mA to 500mA
0.13
0.001
CONDITIONS
MAX748A
TYP
MAX
16.0
3.3
3.465
MAX763A
TYP
MAX
11.0
UNITS
V
MIN
3.3
3.135
MIN
3.3
3.135
3.3
3.465
3.135
3.3
3.465
3.135
3.3
3.465
V
3.135
3.3
3.465
Output Voltage
3.135
3.3
3.465
3.135
3.3
3.465
3.135
3.3
0.13
0.001
3.465
%/V
%/mA
2
________________________________________________________________________________________________
3.3V, Step-Down,
Current-Mode PWM DC-DC Converters
MAX748A/MAX763A
ELECTRICAL CHARACTERISTICS (continued)
(Circuit of Figure 3, V+ = 5V, I
LOAD
= 0mA, T
A
= T
MIN
to T
MAX
, unless otherwise noted.)
PARAMETER
Efficiency
Supply Current
Shutdown Current
Shutdown Input
Threshold
Shutdown Input
Leakage Current
Short-Circuit Current
Undervoltage Lockout
LX On Resistance
LX Leakage Current
Reference Voltage
Reference Drift
Oscillator Frequency
Compensation Pin
Impedance
V+ falling
I
LX
= 500mA
V+ = 12V, LX = 0
T
A
= +25°C
T
A
= T
MIN
to T
MAX
159
1.15
1.2
2.7
1.0
10
1.22
50
180
7500
212.5
159
1.30
1.15
3.0
V+ = 5V
CONDITIONS
I
LOAD
= 300mA
I
LOAD
= 100mA
Includes switch current
SHDN
= 0V (Note 1)
V
IH
V
IL
2.0
0.25
1.0
1.2
2.7
1.0
10
1.22
50
200
7500
212.5
1.30
3.0
MAX748A
TYP
MAX
88
90
1.7
0.2
3.0
100.0
2.0
0.25
1.0
µA
A
V
Ω
nA
V
ppm/°C
kHz
Ω
MAX763A
TYP
MAX
88
90
1.4
0.2
2.5
100.0
mA
µA
V
UNITS
%
MIN
MIN
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.
________________________________________________Typical Operating Characteristics
(Circuit of Figure 3, T
A
= +25°C, V
OUT
= 3.3V, unless otherwise noted.)
MAXIMUM OUTPUT CURRENT
vs. SUPPLY VOLTAGE
1000
MAX748A
MAXIMUM OUTPUT CURRENT (mA)
800
MAX763A
EFFICIENCY (%)
600
90
85
80
75
70
NOTE 2
NOTE 2
65
60
0
2
4
6
8
10 12
SUPPLY VOLTAGE (V)
14
16
0
100 200 300 400 500 600 700 800
OUTPUT CURRENT (mA)
65
60
0
100 200 300 400 500 600 700 800 900
OUTPUT CURRENT (mA)
VIN = 11.0V
EFFICIENCY (%)
90
85
80
75
70
VIN = 9V
VIN = 12V
NOTE 2
VIN = 16V
100
95
VIN = 7.0V
VIN = 5.0V
MAX763A
EFFICIENCY vs. OUTPUT CURRENT
100
95
MAX748A
EFFICIENCY vs. OUTPUT CURRENT
VIN = 4.5V
VIN = 6V
400
200
0
_________________________________________________________________________________________________
3
3.3V, Step-Down,
Current-Mode PWM DC-DC Converters
MAX748A/MAX763A
____________________________Typical Operating Characteristics (continued)
(Circuit of Figure 3, T
A
= +25°C, V
OUT
= 3.3V, unless otherwise noted.)
MAX763A
QUIESCENT SUPPLY CURRENT
vs. SUPPLY VOLTAGE
4.5
QUIESCENT SUPPLY CURRENT (mA)
QUIESCENT SUPPLY CURRENT (mA)
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
SUPPLY VOLTAGE (V)
9 10 11 12
0
0
2
4
6
8
10 12
SUPPLY VOLTAGE (V)
14
16
0
0 50 100 150 200 250 300 350 400 450 500 550
OUTPUT CURRENT (mA)
TA = -55°C
TA = +25°C
IOUT = 0mA
TA = +125°C
5.0
IOUT = OmA
4.0
TA = -55°C
3.0
TA = +125°C
TA = +25°C
1.0
PEAK INDUCTOR CURRENT (mA)
800
VIN = 11V
MAX748A
QUIESCENT SUPPLY CURRENT
vs. SUPPLY VOLTAGE
1000
PEAK INDUCTOR CURRENT
vs. OUTPUT CURRENT
600
400
VIN = 6V
VIN = 8V
2.0
200
OSCILLATOR FREQUENCY
vs. SUPPLY VOLTAGE
275
250
OSCILLATOR FREQUENCY (kHz)
SHUTDOWN CURRENT (µA)
225
MAX748A
200
175
150
125
100
0
2
4
6
8
10 12
SUPPLY VOLTAGE (V)
14
16
MAX763A
3.5
3.0
2.5
2.0
1.5
1.0
0.5
0
SHUTDOWN CURRENT
vs. TEMPERATURE
4.0
NOTES 3, 4
3.5
OUTPUT VOLTAGE (V)
3.0
2.5
2.0
1.5
1.0
IOUT = 0mA
V+ = 5V
0.5
0
-60 -40 -20
0
20 40 60 80 100 120 140
2.0
2.5
OUTPUT VOLTAGE
vs. SUPPLY VOLTAGE
ILOAD = 50mA
ILOAD = 200mA
ILOAD = 500mA
ILOAD = 300mA
3.0
3.5
4.0
4.5
5.0
TEMPERATURE (°C)
SUPPLY VOLTAGE (V)
OUTPUT VOLTAGE
vs. OUTPUT CURRENT
4.0
3.5
3.0
OUTPUT VOLTAGE (V)
2.5
2.0
1.5
1.0
0.5
0
0
50 100 150 200 250 300 350 400 450 500
OUTPUT CURRENT (mA)
VIN = 3.5V
VIN = 3.0V
VIN = 4.0V
OSCILATOR FREQUENCY (kHz)
250
200
150
100
50
0
300
OSCILLATOR FREQUENCY
vs. TEMPERATURE
IOUT = 100mA
V+ = 5V
MAX748A
MAX763A
-60 -40 -20
0
20 40 60 80 100 120 140
TEMPERATURE (°C)
4
_______________________________________________________________________________________
3.3V, Step-Down,
Current-Mode PWM DC-DC Converters
_________________________________Typical Operating Characteristics (continued)
(Circuit of Figure 3, T
A
= +25°C, V
OUT
= 3.3V, unless otherwise noted.)
MAX748A/MAX763A
SWITCHING WAVEFORMS,
CONTINUOUS CONDUCTION
SWITCHING WAVEFORMS,
DISCONTINUOUS CONDUCTION
6V
A
0V
400mA
B
0mA
C
6V
A
0V
200mA
B
0mA
C
2µs/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
2µs/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
LINE-TRANSIENT RESPONSE
LOAD-TRANSIENT RESPONSE
A
A
500mA
10V
7V
0V
B
0mA
B
5ms/div
A: VOUT, 50mV/div
B: V+, 5V/div, 7.0V TO 10.0V
IOUT = 350mA
5ms/div
A: VOUT, 50mV/div
B: IOUT, 200mA/div, 0mA TO 500mA
V+ = 6V
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 = +85°C.
_______________________________________________________________________________________
5
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