__________________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.
___________________________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
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
GNDSS
REF
SHDNON/OFF
22µHOUTPUT
3.3V
100µF
____________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, ILOAD = 0mA, TA= TMIN to TMAX, 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 < ILOAD < 300mA
M temp. range,
V+ = 4.0V to 16V, 3.135 3.3 3.465
0mA < ILOAD < 250mA
C/E temp. ranges,
V+ = 4.75V to 16V, 3.135 3.3 3.465
0mA < ILOAD < 500mA
M temp. range,
V+ = 4.75V to 16V, 3.135 3.3 3.465
Output Voltage 0mA < ILOAD < 400mA V
C/E temp. ranges,
V+ = 4.0V to 11V, 3.135 3.3 3.465
0mA < ILOAD < 300mA
M temp. range,
V+ = 4.0V to 11V, 3.135 3.3 3.465
0mA < ILOAD < 250mA
C/E temp. ranges,
V+ = 4.75V to 11V, 3.135 3.3 3.465
0mA < ILOAD < 500mA
M temp. range,
V+ = 4.75V to 11V, 3.135 3.3 3.465
0mA < ILOAD < 400mA
Line Regulation 0.13 0.13 %/V
Load Regulation ILOAD = 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 (ILX).....................................................2.0A
Reference Current (IREF)...................................................2.5mA
Continuous Power Dissipation (TA= +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
MAX748A/MAX763A
3.3V, Step-Down,
Current-Mode PWM DC-DC Converters
_________________________________________________________________________________________________
3
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.
MAXIMUM OUTPUT CURRENT
vs. SUPPLY VOLTAGE
MAXIMUM OUTPUT CURRENT (mA)
0
200
400
600
800
1000
0246810121416
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, TA = +25°C, VOUT = 3.3V, unless otherwise noted.)
PARAMETER CONDITIONS MAX748A MAX763A UNITS
MIN TYP MAX MIN TYP MAX
Efficiency V+ = 5V ILOAD = 300mA 88 88 %
ILOAD = 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 µA
Shutdown Input VIH 2.0 2.0 V
Threshold VIL 0.25 0.25
Shutdown Input 1.0 1.0 µA
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= TMIN to TMAX 50 50 ppm/°C
Oscillator Frequency 159 180 212.5 159 200 212.5 kHz
Compensation Pin 7500 7500 Ω
Impedance
ELECTRICAL CHARACTERISTICS (continued)
(Circuit of Figure 3, V+ = 5V, ILOAD = 0mA, TA= TMIN to TMAX, unless otherwise noted.)
MAX748A/MAX763A
3.3V, Step-Down,
Current-Mode PWM DC-DC Converters
4 _______________________________________________________________________________________
____________________________Typical Operating Characteristics (continued)
(Circuit of Figure 3, TA = +25°C, VOUT = 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
00 1 2 3 4 5 6 7 8 9 10 11 12
IOUT = 0mA
TA = +125°C
TA = -55°C
TA = +25°C
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 = +125°C
TA = -55°C
TA = +25°C
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 810121416
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 (µA)
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, TA = +25°C, VOUT = 3.3V, unless otherwise noted.)
SWITCHING WAVEFORMS,
CONTINUOUS CONDUCTION
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
6V
0V
400mA
0mA
A
B B
C
SWITCHING WAVEFORMS,
DISCONTINUOUS CONDUCTION
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
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= +85°C.
PIN #
8-PIN DIP/SO 16-PIN WIDE SO NAME FUNCTION
(MAX748A)
12
SHDN
Shutdown—active low. Connect to ground to power down chip; tie to V+ for normal
operation. Output voltage falls to 0V when
SHDN
is low.
2 3 REF Reference Voltage Output (+1.23V) supplies up to 100µA for external loads.
Bypass to GND with a 0.047µF capacitor.
37SS
Soft-Start. Capacitor between SS and GND provides soft-start and
short-circuit protection.
48CC
Compensation Capacitor Input externally compensates the outer (voltage)
feedback loop. Connect to OUT with a 330pF capacitor.
5 9 OUT Output-Voltage Sense Input provides regulation feedback sensing.
Connect to +3.3V output.
6 10, 11 GND Ground*
7 12, 13, 14 LX Drain of internal P-channel power MOSFET*
Supply Voltage Input. Bypass to GND with 1µF ceramic and large-value
8 1,15,16 V+ electrolytic capacitor in parallel. The 1µF capacitor must be as close
to the GND and V+ pins as possible.*
4, 5, 6 N.C. No Connect—no internal connections to these pins.
_________________Detailed Description
The MAX748A/MAX763A switch-mode regulators use a
current-mode pulse-width-modulation (PWM) control
system in a step-down (buck) regulator topography.
They convert an unregulated DC input voltage from 4V
to 11V (MAX763A) or from 4V to 16V (MAX748A) to a
regulated 3.3V output at 300mA. For loads less than
300mA, V+ may be less than 4.0V (see the Output
Voltage vs. Supply Voltage graph in the
Typical
Operating Characteristics
). The current-mode
PWM architecture provides cycle-by-cycle current limit-
ing, improved load-transient response, and simpler
outerloop design.
The controller consists of two feedback loops: an inner
(current) loop that monitors the switch current via the
current-sense resistor and amplifier, and an outer (volt-
age) loop that monitors the output voltage through the
error amplifier (Figure 1). The inner loop performs
cycle-by-cycle current limiting, truncating the power
transistor on-time when the switch current reaches a
predetermined threshold. This threshold is determined
by the outer loop. For example, a sagging output volt-
age produces an error signal that raises the threshold,
allowing the circuit to store and transfer more energy
during each cycle.
Programmable Soft-Start
Figure 2 shows a capacitor connected to the soft-start
(SS) pin to ensure orderly power-up. A typical value is
0.047µF. SS controls both the SS timing and the maxi-
mum output current that can be delivered while main-
taining regulation.
The charging capacitor slowly raises the clamp on the
error-amplifier output voltage, limiting surge currents
at power-up by slowly increasing the cycle-by-cycle
current-limit threshold. Table 1 lists timing characteris-
tics for selected capacitor values and circuit conditions.
The overcurrent comparator trips when the load exceeds
approximately 1.2A. When either an undervoltage or over-
current fault condition is detected, an SS cycle is actively
initiated, which triggers an internal transistor to discharge
the SS capacitor to ground. An SS cycle is also enabled
at power-up and when coming out of shutdown mode.
Overcurrent Limiting
The overcurrent comparator triggers when the load
current exceeds approximately 1.2A. On each clock
cycle, the output FET turns on and attempts to deliver
current until cycle-by-cycle or overcurrent limits are
exceeded. Note that the SS capacitor must be greater
than 0.01µF for overcurrent protection to function prop-
erly. A typical value is 0.047µF.
MAX748A/MAX763A
3.3V, Step-Down,
Current-Mode PWM DC-DC Converters
6 _______________________________________________________________________________________
_______________________________________________________________________Pin Description
*16-pin wide SO package: All pins sharing the same name must be connected together externally.
MAX748A/MAX763A
3.3V, Step-Down,
Current-Mode PWM DC-DC Converters
_______________________________________________________________________________________ 7
SHDN
BIAS
GEN
OUT
CC
C5
330pF
1.23V
BANDGAP
ERROR AMP
C6
1000pF
REF
SS
1M
±35%
C1
0.047µF
Σ
RAMP
GEN
SLOPE COMPENSATION
OVERCURRENT COMPARATOR
CURRENT
SENSE AMP
RSENSE
F/F
S
RQ
PWM
COMPARATOR
SS CLAMP
200kHz
OSC
GND
VUVLO
UNDERVOLTAGE
LOCKOUT
D1
1N5817 C4
150µF
VOUT
3.3V
L1
22µH
LX
C2
1.0µF
VIN
V+
C3
150µF
MAX748A
MAX763A
MAX748A 3.3V to 16.0V
MAX763A 3.3V to 11.0V
Figure 1. Detailed Block Diagram with External Components
Circuit Cond. Soft-Start Time (ms) vs. C1 (µF)
V+ (V) IOUT (mA) C1 = 0.01 C1 = 0.047 C1 = 0.1 C1 = 0.47
80 1 4 712
12* 0 1 2 3 6
8 200 10 33 50 200
12* 200 7 17 20 80
8 300 13 44 65 325
12* 300 8 25 35 140
* MAX748A only
Table 1. Typical Soft-Start Times
(Circuit of Figure 3, C4 = 150µF)
FROM SHDN
C1
SS
SS CLAMP
1M
±35%
1.23V
MAX748A
MAX763A
Figure 2. Soft-Start Circuitry Block Diagram
MAX748A/MAX763A
3.3V, Step-Down,
Current-Mode PWM DC-DC Converters
8 _______________________________________________________________________________________
Production Method Inductors Capacitors
Sumida Matsuo
CD105 series 267 series
Surface Mount Coiltronics Sprague
CTX series 595D/293D series
Coilcraft
DT series
High Performance/ Sumida Sanyo
Miniature Through-Hole RCH895 series OS-CON series (very low ESR)
Through-Hole Renco Nichicon
RL1284 series PL series (low ESR)
Phone and FAX Numbers:
Coilcraft USA: (708) 639-6400, FAX: (708) 639-1469 Renco USA: (516) 586-5566, FAX: (516) 586-5562
Coiltronics USA: (305) 781-8900, FAX: (305) 782-4163 Sanyo USA: (0720) 70-1005, FAX: (0720) 70-1174
Matsuo USA: (714) 969-2491, FAX: (714) 960-6492 Sprague Elec. Co. USA: (603) 224-1961, FAX: (603) 224-1430
Japan: (06) 332-0871 Sumida USA: (708) 956-0666, FAX: (708) 956-0702
Nichicon USA: (708) 843-7500, FAX: (708) 843-2798
Japan: (03) 3607-5111, FAX: (03) 3607-5428
Table 3. External Component Suppliers
normal operation, connect
SHDN
to V+. Coming out of
shutdown mode initiates an SS cycle.
Continuous-/Discontinuous-
Conduction Modes
The input voltage, output voltage, load current, and
inductor value determine whether the IC operates in
continuous or discontinuous mode. As the inductor
value or load current decreases, or the input voltage
increases, the MAX748A/MAX763A tend to operate in
discontinuous-conduction mode (DCM). In DCM, the
inductor current slope is steep enough so it decays to
zero before the end of the transistor off-time. In contin-
uous-conduction mode (CCM), the inductor current
never decays to zero, which is typically more efficient
than DCM. CCM allows the MAX748A/MAX763A to
deliver maximum load current, and is also slightly less
noisy than DCM, because it doesn’t exhibit the ringing
that occurs when the inductor current reaches zero.
Internal Reference
The +1.23V bandgap reference supplies up to 100µA
at REF. A 1000pF bypass capacitor from REF to GND
is required.
Oscillator
The MAX748A/MAX763A’s internal oscillator is guaran-
teed to operate in the 159kHz to 212.5 kHz range over
temperature for V+ = 5V. Temperature stability over the
military temperature range is about 0.04%/°C.
Undervoltage Lockout
The undervoltage lockout feature monitors the supply
voltage at V+ and allows operation to start when V+
rises above 2.95V. When V+ falls, operation continues
until the supply voltage falls below 2.7V (typ). When an
undervoltage condition is detected, control logic turns
off the output power FET and discharges the SS capac-
itor to ground. This prevents partial turn-on of the power
MOSFET and avoids excessive power dissipation. The
control logic holds the output power FET off until the
supply voltage rises above approximately 2.95V, at
which time an SS cycle begins. When the input voltage
exceeds the undervoltage lockout threshold, switching
action will occur, but the output will not be regulated
until the input voltage exceeds 3.3V (no load). The
exact input voltage required for regulation depends on
load conditions (see the Output Voltage vs. Supply
Voltage graph in the
Typical Operating Characteristics
).
Shutdown Mode
The MAX748A/MAX763A are held in shutdown mode
by keeping
SHDN
at ground. In shutdown mode, the
output drops to 0V and the output power FET is held in
an off state. The internal reference also turns off, which
causes the SS capacitor to discharge. Typical supply
current in shutdown mode is 0.2µA. The actual design
limit for shutdown current is much less than the 100µA
specified in the
Electrical Characteristics
. However,
testing to tighter limits is prohibitive because the cur-
rent takes several seconds to settle to a final value. For
MAX748A/MAX763A
3.3V, Step-Down,
Current-Mode PWM DC-DC Converters
_______________________________________________________________________________________ 9
____________Applications Information
Fixed +3.3V Step-Down
Converter Application
Figure 3 shows the standard 3.3V step-down circuit with
components shown for commercial temperature range
applications. Figures 4, 5, and Table 2 suggest external
component values for both SO and through-hole wide
temperature range applications. These circuits are use-
ful in systems that require high current and high efficien-
cy and are powered by an unregulated supply, such as
a battery or wall-plug AC-DC adapter.
The MAX748A delivers a guaranteed 300mA for input
voltages of 4V to 16V, and a guaranteed 500mA for
input voltages of 4.75V to 16V with 800mA typical out-
put currents. The MAX763A delivers a guaranteed
300mA for input voltages of 4V to 11V, a guaranteed
500mA for input voltages of 4.75V to 11V, and has
700mA typical output currents. The MAX748A/
MAX763A operate from an input down to 3V (the upper
limit of undervoltage lockout), but with some reduction
in output voltage and maximum output current.
Inductor Selection
The MAX748A/MAX763A require no inductor design
because they are tested in-circuit, and are guaranteed
to deliver the power specified in the
Electrical
Characteristics
with high efficiency using a single
22µH inductor. The 22µH inductor’s incremental satu-
ration current rating should be greater than 1A for
500mA load operation. Table 3 lists inductor types and
suppliers for various applications. The surface-mount
inductors have nearly equivalent efficiencies to the
larger through-hole inductors.
Output Filter Capacitor Selection
The primary criterion for selecting the output filter
capacitor is low effective series resistance (ESR). The
product of the inductor-current variation and the output
capacitor’s ESR determines the amplitude of the saw-
tooth ripple seen on the output voltage. Minimize the
output filter capacitor’s ESR to maintain AC stability.
Table 2. Component Table for
Wide Temperature Applications
C1(µF) C2(µF) C3(µF) C4(µF) C5(pF) C6(pF) L1(µH)
Through-
Hole 0.047 1.0 150* 220* 330 1000 22
SO 0.047 1.0 68** 100*** 330 1000 22
* Sanyo OS-CON Series (very low ESR)
** 16V or greater maximum voltage rating.
*** 6.3V or greater maximum voltage rating.
L2
25µHFILTER
OUTPUT
OUTPUT C7
2.2µF
OPTIONAL 21kHz LOWPASS OUTPUT FILTER
MAX748A
MAX763A
SHDN
D1
1N5817
C5
330pF
L1
22µH
C4
150µF
OUTPUT
3.3V
C2
1.0µF
C3
150µF
8
1LX
V+
OUT
CCSS
GND
3
62
C6
1000pF
C1
0.047µF
INPUT
MAX748A 3.3V TO 16.0V
MAX763A 3.3V TO 11.0V VIN
7
5
4
REF
Figure 3. Standard 3.3V Step-Down Application Circuit Using Through-Hole Components (commercial temperture range)
MAX748A/MAX763A
3.3V, Step-Down,
Current-Mode PWM DC-DC Converters
10 ______________________________________________________________________________________
The capacitor’s ESR should be less than 0.25Ωto keep
the output ripple less than 50mVp-p over the entire cur-
rent range (using a 22µH inductor). Capacitor ESR
usually rises at low temperatures, but OS-CON capaci-
tors provide very low ESR below 0°C. Table 3 lists
capacitor suppliers.
Other Components
The catch diode should be a Schottky or high-speed
silicon rectifier with a peak current rating of at least
1.0A for full-load (500mA) operation. The 1N5817 is a
good choice. The 330pF outer-loop compensation
capacitor provides the widest input voltage range and
best transient characteristics.
Printed Circuit Layouts
A good layout is essential for stable, low-noise opera-
tion. The layouts and component placement diagrams
MAX748A
MAX763A
SHDN
D1
1N5817
C5
330pF
L1
22µH
C4*
220µF
(10V)
OUTPUT
3.3V
C2
1.0µF
C3*
150µF
(16V)
8
1LX
V+
OUT
CCSS
REF
GND
3
62
C6
1000pF
C1
0.047µF
INPUT
MAX748A 3.3V TO 16.0V
MAX763A 3.3V TO 11.0V VIN
7
5
4
*OS-CON Series (very low ESR)
MAX748A
MAX763A
SHDN
D1
1N5817
C5
330pF
L1
22µH
C4*
100µF
(6.3V)
OUTPUT
3.3V
C2
1.0µF
C3*
68µF
(16V)
8
1LX
V+
OUT
CCSS
REF
GND
3
62
C6
1000pF
C1
0.047µF
INPUT
MAX748A 3.3V TO 16.0V
MAX763A 3.3V TO 11.0V VIN
7
5
4
*Sprague 293D or 595D Series-16V. See Table 3
for alternative suppliers.
in Figures 6-9 have been tested successfully over a
wide range of operating conditions. The 1µF input
bypass capacitor must be positioned as close to
the V+ and GND pins as possible. Also, place the
output capacitor as close to the OUT and GND pins as
possible. The traces connecting ground to the input
and output filter capacitors and to the catch diode
must be short to reduce inductance. Use an uninter-
rupted ground plane if possible.
Output-Ripple Filtering
A simple lowpass pi-filter (Figure 3) can be added to
the output to reduce output ripple to about 5mVp-p.
The cutoff frequency shown is 21kHz. Since the filter
inductor is in series with the circuit output, minimize the
filter inductor’s resistance so the voltage drop across it
is not excessive.
Figure 4. Standard 3.3V Step-Down Application Circuit Using
Through-Hole Components (all temperature ranges) Figure 5. Standard 3.3V Step-Down Application Circuit Using
Surface-Mount Components (Commercial and Extended
Industrial Temperature Ranges)
MAX748A/MAX763A
3.3V, Step-Down,
Current-Mode PWM DC-DC Converters
______________________________________________________________________________________ 11
Figure 6. DIP PC Layout, Through-Hole Component Placement
Diagram (1X Scale)
Figure 8. DIP PC Layout, Solder Side (1X Scale) Figure 9. DIP PC Layout, Drill Guide (1X Scale)
Figure 7. DIP PC Layout, Component Side (1X Scale)
MAX748A/MAX763A
3.3V, Step-Down,
Current-Mode PWM DC-DC Converters
12 ______________________________________________________________________________________
PART TEMP. RANGE PIN-PACKAGE
MAX763ACPA 0°C to +70°C 8 Plastic DIP
MAX763ACSA 0°C to +70°C 8 SO
MAX763AC/D 0°C to +70°C Dice*
MAX763AEPA -40°C to +85°C 8 Plastic DIP
MAX763AESA -40°C to +85°C 8 SO
MAX763AMJA -55°C to +125°C 8 CERDIP
_Ordering Information (continued)
* Contact factory for dice specifications.
TOP VIEW
16
15
14
13
12
11
10
9
1
2
3
4
5
6
7
8
V+
V+
LX
LX
N.C.
REF
V+
MAX748A
LX
GND
GND
OUT
CC
SS
N.C.
N.C.
Wide SO
SHDN
1
2
3
4
8
7
6
5
V+
LX
GND
OUT
CC
SS
REF
MAX748A
MAX763A
SO
SHDN
_____Pin Configurations (continued)
SS REF
SHDN
V+
V+
V+
LXLX LX
GND
GND
OUT
CC
0.116"
2.946mm
0.131"
3.327mm
TRANSISTOR COUNT: 298
SUBSTRATE CONNECTION: V+
OUTCC
SS
REF
GND
LX
LX
LX
SHDN
V+ V+ V+
0.116"
2.946mm
0.072"
1.829mm
TRANSISTOR COUNT: 281
SUBSTRATE CONNECTION: V+
MAX748A
MAX763A
V+
____________________Chip Topographies
