__________________General Description
The MAX730A/MAX738A/MAX744A are 5V-output
CMOS, step-down switching regulators. The MAX738A/
MAX744A accept inputs from 6V to 16V and deliver
750mA. The MAX744A guarantees 500mA load capa-
bility for inputs above 6V and has tighter oscillator fre-
quency limits for low-noise (radio) applications. The
MAX730A accepts inputs between 5.2V and 11V and
delivers 450mA for inputs above 6V. Typical efficien-
cies are 85% to 96%. Quiescent supply current is
1.7mA and only 6µA in shutdown.
Pulse-width modulation (PWM) current-mode control
provides precise output regulation and excellent tran-
sient responses. Output voltage accuracy is guaran-
teed to be ±5% over line, load, and temperature varia-
tions. Fixed-frequency switching allows easy filtering of
output ripple and noise, as well as the use of small
external components. These regulators require only a
single inductor value to work in most applications, so
no inductor design is necessary.
The MAX730A/MAX738A/MAX744A also feature cycle-
by-cycle current limiting, overcurrent limiting, undervolt-
age lockout, and programmable soft-start protection.
___________________________Applications
Portable Instruments
Cellular Phones and Radios
Personal Communicators
Distributed Power Systems
Computer Peripherals
________________________________Features
♦750mA Load Currents (MAX738A/MAX744A)
♦High-Frequency, Current-Mode PWM
♦159kHz to 212.5kHz Guaranteed Oscillator
Frequency Limits (MAX744A)
♦85% to 96% Efficiencies
♦1.7mA Quiescent Current
♦6µA Shutdown Supply Current
♦Single Preselected Inductor Value,
No Component Design Required
♦Overcurrent, Soft-Start, and Undervoltage
Lockout Protection
♦Cycle-by-Cycle Current Limiting
♦8-Pin DIP/SO Packages (MAX730A)
_________________Ordering Information
Ordering Information continued at end of data sheet.
*Contact factory for dice specifications.
MAX730A/MAX738A/MAX744A
5V, Step-Down,
Current-Mode PWM DC-DC Converters
________________________________________________________________
Maxim Integrated Products
1
TOP VIEW
1
2
3
4
8
7
6
5
V+
LX
GND
OUT
CC
SS
REF
MAX730A
MAX738A
MAX744A
DIP
SHDN
Pin Configurations continued on last page.
_________________Pin Configurations
MAX738A
MAX744A
INPUT
6V TO 16V
V+ LX
OUT
CC
GNDSS
REF
SHDNON/OFF
33µHOUTPUT
5V
100µF
68µF
__________Typical Operating Circuit
19-0165; Rev 2; 1/96
For free samples & the latest literature: http://www.maxim-ic.com, or phone 1-800-998-8800
PART TEMP. RANGE PIN-PACKAGE
MAX730ACPA 0°C to +70°C 8 Plastic DIP
MAX730ACSA 0°C to +70°C 8 SO
MAX730AC/D 0°C to +70°C Dice*
MAX730AEPA 8 Plastic DIP
MAX730AESA -40°C to +85°C 8 SO
-40°C to +85°C
MAX730AMJA -55°C to +125°C 8 CERDIP
MAX730A/MAX738A/MAX744A
5V, Step-Down,
Current-Mode PWM DC-DC Converters
2 _______________________________________________________________________________________
ABSOLUTE MAXIMUM RATINGS
ELECTRICAL CHARACTERISTICS
(Circuit of Figure 3, V+ = 9V for the MAX730A, V+ = 12V for the MAX738A/MAX744A, ILOAD = 0mA, TA= TMIN to TMAX,
unless otherwise noted.)
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.
PARAMETER MAX730A
MIN TYP MAX UNITS
4.75 5.00 5.25
CONDITIONS
Pin Voltages
V+ (MAX730A)......................................................+12V, -0.3V
V+ (MAX738A/MAX744A).....................................+18V, -0.3V
LX (MAX730A) .................................(V+ - 12V) to (V+ + 0.3V)
LX (MAX738A/MAX744A) ................(V+ - 21V) to (V+ + 0.3V)
OUT.................................................................................±25V
SS, CC, SHDN .........................................-0.3V to (V+ + 0.3V)
Peak Switch Current (ILX)........................................................2A
Reference Current (IREF)...................................................2.5mA
Continuous Power Dissipation (TA= +70°C)
8-Pin Plastic DIP (derate 9.09mW/°C above +70°C)...727mW
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_ _/AE_ _...................................................+150°C
MAX7_ _AMJA.............................................................+175°C
Storage Temperature Range ............................-65°C to +160°C
Lead Temperature (soldering, 10sec).............................+300°C
0mA < ILOAD < 450mA,
MAX730AC
0mA < ILOAD < 450mA,
MAX730AE
0mA < ILOAD < 300mA,
MAX730AM
0mA < ILOAD < 450mA,
MAX738AC/AE
0mA < ILOAD < 350mA,
MAX738AM
0mA < ILOAD < 500mA,
MAX744AC/AE
0mA < ILOAD < 375mA,
MAX744AM
MAX738A
MIN TYP MAX
4.75 5.00 5.25
4.75 5.00 5.25
MAX744A
MIN TYP MAX
4.75 5.00 5.25
4.75 5.00 5.25
Output Voltage V
V+ = 9.0V
to 16.0V
6.0 16.0 6.0 16.05.2 11.0 V
V+ = 5.2V to 11.0V 0.15
V+ = 6.0V to 16.0V 0.15 0.15 %/V
Line Regulation
V+ = 6.0V
to 16.0V
V+ = 6.0V
to 11.0V
V+ = 10.2V to 16.0V,
0mA < ILOAD < 750mA
0mA < ILOAD < 750mA,
MAX744AC/AE
0mA < ILOAD < 600mA,
MAX744AM
Input Voltage
Range
MAX730A/MAX738A/MAX744A
5V, Step-Down,
Current-Mode PWM DC-DC Converters
_______________________________________________________________________________________ 3
Note 1: The standby current typically settles to 25µA (over temperature) within 2 seconds; however, to decrease test time, the part
is guaranteed at a 100µA maximum value.
ELECTRICAL CHARACTERISTICS (continued)
(Circuit of Figure 3, V+ = 9V for the MAX730A, V+ = 12V for the MAX738A/MAX744A, ILOAD = 0mA, TA= TMIN to TMAX,
unless otherwise noted.)
PARAMETER
ILOAD = 0mA to 300mA
MAX730A
MIN TYP MAX
Supply Current
(includes switch
current)
ILOAD = 0mA to 750mA
UNITS
V+ = 9.0V, ILOAD = 300mA
MAX738A
MIN TYP MAX
4.3
mA
MAX744AE
ILX = 500mA
6.0 100.0 6.0 100.06.0 100.0 µAStandby Current VIH
0.0005
LX On Resistance
2.0 2.02.0
MAX744AC/AE
0.5
VIL
MAX744A
MIN TYP MAX
0.25 0.250.25 V
0.5
0.0005
Shutdown Input
Threshold
%/mA
Shutdown Input
Leakage Current
V+ = 12V, ILOAD = 750mA
Load Regulation 0.0005
SHDN = 0V (Note 1)
0.5
1.7 3.0 1.7 3.01.7 3.0
159.0 185.0 212.5
Ω
MAX744AC/AE 1.2 2.5
V+ = 12V, LX = 0V
MAX744AM
1.0
3.0
1.0 1.0
V+ = 6.0V
to 9.0V
MAX744AC/AE 3.0
1.0 µA
Reference Drift
1.01.0
MAX744AM
µA
3.5
1.5
MAX744AM
V+ = 9.0V
to 12.0V
MAX744AC 4.0
50 50
LX Leakage Current
1.5
87
1.5
CONDITIONS
AShort-Circuit Current V+ rising
159.0 216.5
5.7 6.0 5.7 6.04.7 5.2
V+ falling 5.0 5.7 V
kHz
Undervoltage
Lockout
90 87
90 %Efficiency 92
V+ = 6.0V
to 16.0V
V+ = 12V, TA= +25°CReference Voltage 1.15 1.23 1.30 1.15 1.23 1.301.15 1.23 1.30 V
50 130 160 190130 170 210 ppm/°C
Oscillator Frequency
7500 75007500 Ω
Compensation Pin
Impedance
4.5
V+ = 12.0V
to 16.0V MAX744AM
100
90
80
60 0 200 600 800 1000
OUTPUT CURRENT (mA)
EFFICIENCY (%)
MAX730A
EFFICIENCY vs. OUTPUT CURRENT
70
400
V+ = 5.5V
V+ = 7V
V+ = 9V
V+ = 11V
(NOTES 3, 6) 100
90
80
60 0 200 600 800 1000
OUTPUT CURRENT (mA)
EFFICIENCY (%)
MAX738A
EFFICIENCY vs. OUTPUT CURRENT
70
400
V+ = 6V
V+ = 8V
V+ = 12V
V+ = 16V
(NOTES 3, 6)
2.5
2.0
1.5
002 6810
QUIESCENT SUPPLY CURRENT (mA)
MAX738A/MAX744A
QUIESCENT SUPPLY CURRENT
vs. SUPPLY VOLTAGE
0.5
4
1.0
12 14 16
UNDERVOLTAGE
LOCKOUT HYSTERESIS
UNDERVOLTAGE
LOCKOUT ENABLED
1000
800
600
00 100 300 400 500
PEAK INDUCTOR CURRENT (mA)
MAX738A/MAX744A
PEAK INDUCTOR CURRENT 
vs. OUTPUT CURRENT
200
200
400
600 700 800
L1 = 100µH
C4 = 150µF
V+ = 6.6V V+ = 8.0V TO 16.0V
MAX730A/MAX738A/MAX744A
5V, Step-Down,
Current-Mode PWM DC-DC Converters
4 _______________________________________________________________________________________
__________________________________________Typical Operating Characteristics
(Circuit of Figure 3, TA = +25°C, unless otherwise noted.)
100
90
80
60 0 200 600 800 100
0
OUTPUT CURRENT (mA)
EFFICIENCY (%)
MAX744A
EFFICIENCY vs. OUTPUT CURRENT
70
400
V+ = 6.0V
V+ = 9.0V
V+ = 12.0V
V+ = 16.0V
(NOTE 3)
-60 0 60 80 100
STANDBY SUPPLY CURRENT (µA)
STANDBY SUPPLY CURRENT 
vs. TEMPERATURE
16
10
6
2
18
14
12
8
4
0-40 -20 20 40 120 140 160
V+ = 16V
MAX738A/MAX744A
ONLY
V+ = 9V
V+ = 6V
(NOTES 4, 5)
20
V+ = 12V
MAX738A/MAX744A
ONLY
3.0
2.5
1.5
1.0
0.5
-60 20 40 80 120
TEMPERATURE (°C)
QUIESCENT SUPPLY CURRENT (mA)
QUIESCENT SUPPLY CURRENT 
vs. TEMPERATURE
2.0
0-40 -20 0 60 100 140 160
MAX730A, V+ = 9.0V
MAX738A, V+ = 12.0V
MAX744A, V+ = 12.0V
(NOTES 4, 5)
1400
1000
4 8 10 12 14
SUPPLY VOLTAGE (V)
MAXIMUM OUTPUT CURRENT (mA)
MAXIMUM OUTPUT CURRENT vs.
SUPPLY VOLTAGE
1200
800 616
MAX738A
MAX730A
MAX744A
(NOTES 3, 6) 1400
1000
800
4 8 10 12 14
SUPPLY VOLTAGE (V)
MAXIMUM OUTPUT CURRENT (mA)
MAXIMUM OUTPUT CURRENT vs.
SUPPLY VOLTAGE, NO R1
1200
616
600
400
200
(NOTES 3, 6)
MAX738A
MAX730A
MAX744A
MAX730A/MAX738A/MAX744A
5V, Step-Down,
Current-Mode PWM DC-DC Converters
_______________________________________________________________________________________
5
____________________________Typical Operating Characteristics (continued)
(Circuit of Figure 3, TA = +25°C, unless otherwise noted.)
46810 14
SUPPLY VOLTAGE (V)
OSCILLATOR FREQUENCY (kHz)
OSCILLATOR FREQUENCY vs.
SUPPLY VOLTAGE
12 16
MAX744A
MAX738A
MAX730A
(NOTE 3)
220
170
160
150
180
190
200
210
210
190
180
-60 20 40 80 120
TEMPERATURE (°C)
OSCILLATOR FREQUENCY (kHz)
MAX744A
OSCILLATOR FREQUENCY 
vs. TEMPERATURE
200
170 -40 -20 0 60 100 140 160
V+ = 6.0V
V+ = 16.0V
V+ = 9.0V
V+ = 12.0V
(NOTE 4)
200
180
170
160
-60 20 40 80 120
TEMPERATURE (°C)
SUPPLY CURRENT (mA)
MAX738A
OSCILLATOR FREQUENCY
vs. TEMPERATURE
190
140
-40 -20 0 60 100 140 160
150
130
120
V+ = 6.0V
V+ = 16.0V
V+ = 12.0V
V+ = 9.0V
(NOTE 4)
-60 20 40 80 120
TEMPERATURE (°C)
OSCILLATOR FREQUENCY (kHz)
MAX730A
OSCILLATOR FREQUENCY 
vs. TEMPERATURE
-40 -20 0 60 100 140 160
240
200
180
160
220
0
140 V+ = 9.0V
V+ = 7.0V
(NOTE 4)
V+ = 5.5V
V+ = 11.0V
Note 3: Commercial temperature range external component values in Table 3.
Note 4: Wide temperature range external component values in Table 3.
Note 5: Standby and shutdown current includes all external component leakage currents. Capacitor leakage currents dominate at T
A> +85°C,
Sanyo OS-CON capacitors were used.
Note 6: Operation beyond the specifications listed in the electrical characteristics may exceed the power dissipation ratings of the device.
MAX730A/MAX738A/MAX744A
5V, Step-Down,
Current-Mode PWM DC-DC Converters
6 _______________________________________________________________________________________
MAX738A/MAX744A
SWITCHING WAVEFORMS,
CONTINUOUS CONDITION
2µs/div
A: SWITCH VOLTAGE (LX PIN), 5V/div, 0V TO +12V
B: INDUCTOR CURRENT, 200mA/div
C: OUTPUT VOLTAGE RIPPLE, 50mV/div, AC-COUPLED
COUT = 390µF,
V+ = 12V, IOUT = 150µA,
MAX738A/MAX744A
SWITCHING WAVEFORMS,
DISCONTINUOUS CONDITION
2µs/div
A: SWITCH VOLTAGE (LX PIN), 5V/div, 0V TO +12V
B: INDUCTOR CURRENT, 200mA/div
C: OUTPUT VOLTAGE RIPPLE, 50mV/div, AC-COUPLED
COUT = 390µF,
V+ = 12V, IOUT = 150µA
12V
0V
200mA
0mA
A
B
C
0V
200mA
0mA
A
B
C
MAX730A LINE-TRANSIENT RESPONSE
100ms/div
A: VOUT, 50mV/div, DC-COUPLED
B: V+, 5V/div, 6.0V TO 11.0V
IOUT = 300mA
MAX738A/MAX744A LINE-TRANSIENT RESPONSE
100ms/div
A: VOUT, 50mV/div, DC-COUPLED
B: V+, 5V/div, 10.2V TO 16.0V
IOUT = 750mA
11V
6V
0V
A
B
16V
10.2V
A
B
____________________________Typical Operating Characteristics (continued)
(Circuit of Figure 3, TA = +25°C, unless otherwise noted.)
12V
0V
MAX730A/MAX738A/MAX744A
5V, Step-Down,
Current-Mode PWM DC-DC Converters
_______________________________________________________________________________________ 7
NAME FUNCTION
1SHDN Shutdown—active low. Ground to power-down chip, tie to V+ for normal operation.
Output voltage falls to 0V when SHDN is low.
2 REF
3 SS Soft-Start. Capacitor between SS and GND provides soft-start and short-circuit protection.
510kΩresistor from SS to SHDN provides current boost.
2
3
4 CC Compensation Capacitor Input externally compensates the outer feedback loop.
Connect to OUT with a 330pF capacitor.
5 OUT Output Voltage Sense Input provides regulation feedback sensing. Connect to +5V output.
6 GND Ground pins are internally connected. Connect both pins to ground.
7 LX Drain of internal P-channel power MOSFET.
7
8
9
8 V+ Supply-Voltage Input. Bypass to GND with 1µF ceramic and large-value electrolytic capaci-
tors in parallel. The 1µF capacitor must be as close to V+ and GND pins as possible.
N.C. No Connect—no internal connections to these pins.
10, 11
12, 13, 14
1, 15, 16
4, 5, 6
______________________________________________________________Pin Description
MAX730A
LOAD-TRANSIENT RESPONSE
50ms/div
A: VOUT, 50mV/div, DC-COUPLED
B: IOUT, 200mA/div, 20mA TO 300mA
V+ = 9V
MAX738A/MAX744A
LOAD-TRANSIENT RESPONSE
50ms/div
A: VOUT, 50mV/div, DC-COUPLED
B: IOUT, 500mA/div, 50mA TO 750mA
V+ = 12V
300mA
20mA
A
B
____________________________Typical Operating Characteristics (continued)
(Circuit of Figure 3, TA = +25°C, unless otherwise noted.)
16-PIN
WIDE SO
8-PIN
DIP/SO
Reference-Voltage Output (+1.23V) supplies up to 100µA for extended loads.
Bypass to GND with a capacitor that does not exceed 0.047µF.
750mA
50mA
A
B
PIN
MAX730A/MAX738A/MAX744A
_________________Detailed Description
The MAX730A/MAX738A/MAX744A switch-mode regu-
lators use a current-mode pulse-width-modulation
(PWM) control system coupled with a simple step-down
(buck) regulator topography. They convert an unregu-
lated DC voltage from 5.2V to 11V for the MAX730A,
and from 6V to 16V for the MAX738A/MAX744A. The
current-mode PWM architecture provides cycle-by-
cycle current limiting, improved load-transient response
characteristics, and simpler outer-loop design.
The controller consists of two feedback loops: an inner
(current) loop that monitors the switch current via the cur-
rent-sense resistor and amplifier, and an outer (voltage)
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 voltage produces an error
signal that raises the threshold, allowing the circuit to
store and transfer more energy during each cycle.
Programmable Soft-Start
Figures 1 and 2 show a capacitor and a resistor con-
nected to the soft-start (SS) pin to ensure an orderly
power-up. Typical values are 0.1µF and 510kΩ. SS con-
trols both the SS timing and the maximum output current
that can be delivered while maintaining 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 cur-
rent-limit threshold. The 510kΩresistor sets the SS
clamp at a value high enough to maintain regulation,
even at currents exceeding 1A. This resistor is not nec-
essary for lower-current loads. Refer to the Maximum
Output Current vs. Supply Voltage graph in the
Typical
Operating Characteristics
. Table 1 lists timing charac-
teristics for selected capacitor values and circuit condi-
tions.
The overcurrent comparator trips when the load
exceeds approximately 1.5A. An SS cycle begins when
either an undervoltage or overcurrent fault condition
triggers an internal transistor to momentarily discharge
the SS capacitor to ground. An SS cycle also begins at
power-up and when coming out of shutdown mode.
Overcurrent Limiting
The overcurrent comparator triggers when the load cur-
rent exceeds approximately 1.5A. 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 properly. A typical
value is 0.1µF.
Undervoltage Lockout
The MAX738A/MAX744A’s undervoltage-lockout fea-
ture monitors the supply voltage at V+, and allows
operation to start when V+ rises above 5.7V (6V guar-
anteed). When V+ falls, operation continues until the
supply voltage falls below 5.45V (see the
MAX738A/MAX744A Quiescent Supply Current vs.
Supply Voltage graph in the
Typical Operating
Characteristics
). The MAX730A is similar, starting oper-
ation at V+ > 4.7V and continuing to operate down to
4.45V. When an undervoltage condition is detected,
control logic turns off the output power FET and dis-
charges the SS capacitor to ground. This prevents par-
tial 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 4.7V (MAX730A) or 5.7V (MAX738A/
MAX744A), at which time an SS cycle begins.
Shutdown Mode
The MAX730A/MAX738A/MAX744A are shut down 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 standby current in
shutdown mode is 6µA. The actual design limit for stand-
by current is much less than the 100µA specified in the
Electrical Characteristics
(see Standby Current vs.
Temperature in the
Typical Operating Characteristics
).
However, testing to tighter limits is prohibitive because
the current takes several seconds to settle to a final value.
For normal operation, connect SHDN to V+. Note that
coming out of shutdown mode initiates an SS cycle.
Continuous-/Discontinuous-
Conduction Modes
The input voltage, output voltage, load current, and induc-
tor value determine whether the IC operates in continuous
or discontinuous mode. As the inductor value or load cur-
rent decreases, or the input voltage increases, the
MAX730A/MAX738A/MAX744A tend to operate in discon-
tinuous-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 continuous-conduc-
tion mode (CCM), the inductor current never decays to
zero, which is typically more efficient than DCM. CCM
allows the MAX730A/ MAX738A/MAX744A to deliver maxi-
mum load current, and is also slightly less noisy than
DCM, because the peak-to-average inductor current ratio
is reduced.
5V, Step-Down,
Current-Mode PWM DC-DC Converters
8 _______________________________________________________________________________________
Internal Reference
The +1.23V bandgap reference supplies up to 100µA
at REF. Connect a 0.01µF bypass capacitor from REF
to GND.
Oscillator
The internal oscillator of the MAX730A typically oper-
ates at 170kHz (160kHz for the MAX738A and 185kHz
for the MAX744A). The MAX744A is guaranteed to
operate at a minimum of 159kHz and a maximum of
212.5kHz over the operating voltage and temperature
range, making it ideal for use in portable communica-
tions systems. The
Typical Operating Characteristics
graphs indicate oscillator frequency stability over tem-
perature and supply voltage.
____________Applications Information
Figure 3 shows the standard 5V step-down application
circuits. Table 3 lists the components for the desired
operating temperature range. These circuits are useful
in systems that require high current at high efficiency
and are powered by an unregulated supply, such as a
battery or wall-plug AC-DC transformer. These circuits
operate over the entire line, load, and temperature
ranges using the single set of component values shown
in Figure 3 and listed in Table 3.
Inductor Selection
The MAX730A/MAX738A/MAX744A 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
MAX730A/MAX738A/MAX744A
5V, Step-Down,
Current-Mode PWM DC-DC Converters
_______________________________________________________________________________________ 9
Table 1. Typical Soft-Start Times
MAX730A CIRCUIT CONDITIONS SOFT-START TIME (ms) vs. C1 (µF)
R1 (kΩ) V+ (V) IOUT (mA) C4 (µF) C1 = 0.01 C1 = 0.047 C1 = 0.1 C1 = 0.47
510 6 0 100 2 6 11 28
510 9 0 100 1 4 6 15
510 11 0 100 1 2 4 11
510 9 150 100 1 4 8 21
510 9 300 100 1 5 9 27
510 9 150 390 3 6 9 23
510 9 150 680 4 6 9 24
None 6 0 100 16 34 51 125
None 9 0 100 10 22 34 82
None 11 0 100 8 18 28 66
None 9 150 100 34 134 270 1263
None 9 150 390 39 147 280 1275
None 9 150 680 40 152 285 1280
MAX738A/MAX744A CIRCUIT CONDITIONS SOFT-START TIME (ms) vs. C1 (µF)
R1 (kΩ) V+ (V) IOUT (mA) C4 (µF) C1 = 0.01 C1 = 0.047 C1 = 0.1 C1 = 0.47
510 7 0 100 1 4 6 18
510 12 0 100 1 2 3 8
510 16 0 100 1 1 2 6
510 12 300 100 1 3 5 3
510 12 750 100 1 5 8 21
None 7 0 100 12 27 40 100
None 12 0 100 7 16 25 54
None 16 0 100 6 13 20 68
None 12 300 100 27 112 215 1114
MAX730A/MAX738A/MAX744A
single 100µH (MAX7__AC) or 33µH (MAX7__AE/AM)
inductor. The inductor’s incremental saturation current
rating should be greater than 1A, and its DC resistance
should be less than 0.8Ω. Table 2 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 equivalent series resistance (ESR).
The product of the inductor current variation and the
output capacitor’s ESR determines the amplitude of the
sawtooth ripple seen on the output voltage. Also, mini-
mize the output filter capacitor’s ESR to maintain AC
stability. The capacitor’s ESR should be less than
0.25Ωto keep the output ripple less than 50mVp-p over
the entire current range (using a 100µH inductor).
Capacitor ESR rises as the temperature falls, and
excessive ESR is the most likely cause of trouble at
temperatures below 0°C. Sanyo OS-CON series
through-hole and surface-mount tantalum capacitors
exhibit low ESR at temperatures below 0°C. Refer to
Table 2 for recommended capacitor values and sug-
gested capacitor suppliers.
Other Components
The catch diode should be a Schottky or high-speed
silicon rectifier with a peak current rating of at least
1.5A for full-load (750mA) operation. The 1N5817 is a
good choice. The 330pF outer-loop compensation
capacitor provides the widest input voltage range and
best transient characteristics. For low-current applica-
tions, the 510kΩresistor may be omitted (see the
Maximum Output Current vs. Supply Voltage graph (R1
removed) in the
Typical Operating Characteristics
).
5V, Step-Down,
Current-Mode PWM DC-DC Converters
10 ______________________________________________________________________________________
C1
0.1µF
SS
REF
CC
OUT
C5
330pF
R1
510k
C6
0.01µF
1M
±35%
GND
SS CLAMP
PWM
COMPARATOR
BIAS
GEN
SHDN
ΣRAMP
GEN
SLOPE COMPENSATION
OVERCURRENT COMPARATOR
RSENSE
CURRENT
SENSE AMP
VIN = +6.0V TO +16.0V
C2
1µF
V+ C3*
VOUT =
+5V
C4*
D1
1N5817
LX
VUVLO
UNDERVOLTAGE
LOCKOUT
OSC
F/F
S
RQ
1.23V
BANDGAP
ERROR AMP
*SEE TABLE 2 FOR COMPONENT VALUES AND SUPPLIERS
L1
MAX730A
MAX738A
MAX744A
Figure 1. Detailed Block Diagram with External Components
Printed Circuit Layouts
A good layout is essential for clean, stable operation.
The layouts and component placement diagrams given
in Figures 4, 5, 6, and 7 have been successfully tested
over a wide range of operating conditions. Note that the
1µF bypass capacitor (C2) must be positioned as close
to the V+ and GND pins as possible. Also, place the out-
put capacitor as close to the OUT and GND pins as pos-
sible. The traces connecting the input and output filter
capacitors and the catch diode must be short to mini-
mize inductance and capacitance. For this reason, avoid
using sockets, and solder the IC directly to the PC
board. Use an uninterrupted 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, its resis-
tance should be minimized so the voltage drop across
it is not excessive.
MAX730A/MAX738A/MAX744A
5V, Step-Down,
Current-Mode PWM DC-DC Converters
______________________________________________________________________________________ 11
Table 2. Component Values and Suppliers
MAX730AC/MAX738AC/MAX744AC
Commercial Temp. Range MAX730AE/M, MAX738AE/M, MAX744AE/M
Wide Temp. Range
Surface
Mount
C3 = 68µF, 16V
C4 = 100µF, 6.3V
Matsuo (714) 969-2491
267 series
Sprague (603) 224-1961
595D/293D series
L1 = 33µH
Sumida (708) 956-0666
CD54-330N (MAX730AC)
CD105-330N
(MAX738AE/M, MAX744AE/M)
Coiltronics (407) 241-7876
CTX50 series
C3 = 68µF, 16V
C4 = 100µF, 6.3V
Matsuo (714) 969-2491
267 series
Sprague (603) 224-1961
595D/293D series
Miniature
Through-
Hole
L1 = 33µH to 100µH
Sumida (708) 956-0666
RCH654-101K (MAX730A)
RCH895-101K
(MAX738A/MAX744A)
C3 = 150µF, 16V
C4 = 150µF, 16V or
390µF, 6.3V
Nichicon (708) 843-7500
PL series
Low-ESR electrolytics
L1 = 33µH
Sumida (708) 956-0666
RCH654-330M (MAX730A)
RCH895-330M
(MAX738A/MAX744A)
Low-Cost
Through-
Hole
Inductors Capacitors Inductors Capacitors
Production
Method
L1 = 33µH to 100µH
Sumida (708) 956-0666
CD54-101KC (MAX730AC)
CD105-101KC
(MAX738AC/MAX744AC)
Coiltronics (407) 241-7876
CTX100 series
C3 = 150µF, 16V
C4 = 220µF, 10V
Sanyo (619) 661-6322
OS-CON series
Low-ESR
organic semiconductor
(Rated from -55°C to +105°C)
Mallory (317) 273-0090
THF series
C3 = 100µF, 20V
C4 = 220µF, 10V
(Rated from -55°C to +125°C)
L1 = 100µH
Maxim
MAXL001
100µH iron-power toroid
Renco (516) 586-5566
RL1284-100
C3 = 150µF, 16V
C4 = 390µF, 6.3V
Maxim
MAXC001
150µF, low-ESR
electrolytic
United Chemicon
(708) 843-7500
MAX730A/MAX738A/MAX744A
5V, Step-Down,
Current-Mode PWM DC-DC Converters
12 ______________________________________________________________________________________
C1
1.23V
1M
±35%
SS
R1
510k SS CLAMP
FROM SHDN
MAX730A
MAX738A
MAX744A
Figure 2. Block Diagram of Soft-Start Circuitry
MAX730A
MAX738A
MAX744A
SHDN V+
1
SS
3
GND REF
62
C6
0.01µF
CC
OUT
4
5
LX 7
D1
1N5817 L1*
OUTPUT
+5V
C4*
C5
330pF
C3*
C2
1µF
8
R1
510k
C1
0.1µF
*SEE TABLE 2 FOR COMPONENT VALUES AND SUPPLIERS.
PART
MAX730A
MAX738A
MAX744A
INPUT SUPPLY RANGE (V)
6.0 to 11.0
6.0 to 16.0
10.2 to 16.0
6.0 to 9.0
9.0 to 16.0
GUARANTEED OUTPUT CURRENT AT 5V (mA)
450
450
750
500
750
NOTE: PIN NUMBERS REFER TO 8-PIN PACKAGES.
C7
2.2µF
OUTPUT
L2
25µHFILTER
OUTPUT
MAX730A +5.2V TO +11.0V
MAX738A/MAX744A +6.0V TO +16.0V OPTIONAL LOWPASS OUTPUT FILTER
Figure 3. Standard +5V Step-Down Application Circuit
MAX730A/MAX738A/MAX744A
5V, Step-Down,
Current-Mode PWM DC-DC Converters
______________________________________________________________________________________ 13
Figure 4. DIP PC Layout, Through-Hole Component Placement
Diagram (1x scale)
Figure 6. DIP PC Layout, Solder Side (1x scale) Figure 7. DIP PC Layout, Drill Guide (1x scale)
Figure 5. DIP PC Layout, Component Side (1x scale)
MAX730 EVALUATION KIT
MAX730A/MAX738A/MAX744A
5V, Step-Down,
Current-Mode PWM DC-DC Converters
14 ______________________________________________________________________________________
1
2
3
4
8
7
6
5
V+
LX
GND
OUT
CC
SS
REF
SHDN
SO
MAX730A
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+
MAX738A
MAX744A
LX
GND
GND
OUT
CC
SS
N.C.
N.C.
Wide SO
SHDN
____Pin Configurations (continued) __Ordering Information (continued)
PART TEMP. RANGE PIN-PACKAGE
MAX738ACPA 0°C to +70°C 8 Plastic DIP
MAX738ACWE 0°C to +70°C 16 Wide SO
MAX738AC/D 0°C to +70°C Dice*
MAX738AEPA -40°C to +85°C 8 Plastic DIP
MAX738AEWE -40°C to +85°C 16 Wide SO
MAX738AMJA -55°C to +125°C 8 CERDIP
MAX744ACPA 0°C to +70°C 8 Plastic DIP
MAX744ACWE 0°C to +70°C 16 Wide SO
MAX744AC/D 0°C to +70°C Dice*
MAX744AEPA -40°C to +85°C 8 Plastic DIP
MAX744AEWE -40°C to +85°C 16 Wide SO
MAX744AMJA -55°C to +125°C 8 CERDIP
*Contact factory for dice specifications.
__________________________________________________________Chip Topographies
LX
GND
REF
SS
SHDN V+
OUT
CC
0.131"
(3.327mm)
0.116"
(2.946mm)
LX
GND
REF
SS
SHDN V+
OUT
CC
0.116"
(2.946mm)
0.072"
(1.828mm)
MAX730A MAX738A/MAX744A
TRANSISTOR COUNT: 274 (MAX730A)
286 (MAX738A/MAX744A);
SUBSTRATE CONNECTED TO V+.
MAX730A/MAX738A/MAX744A
5V, Step-Down,
Current-Mode PWM DC-DC Converters
______________________________________________________________________________________ 15
________________________________________________________Package Information
C
AA2
E1
D
E
eA
eB
A3
B1
B
DIM
A
A1
A2
A3
B
B1
C
D
D1
E
E1
e
eA
eB
L
α
MIN
–
0.015
0.125
0.055
0.016
0.050
0.008
0.348
0.005
0.300
0.240
–
0.115
0˚
MAX
0.200
–
0.175
0.080
0.022
0.065
0.012
0.390
0.035
0.325
0.280
0.400
0.150
15˚
MIN
–
0.38
3.18
1.40
0.41
1.27
0.20
8.84
0.13
7.62
6.10
–
2.92
0˚
MAX
5.08
–
4.45
2.03
0.56
1.65
0.30
9.91
0.89
8.26
7.11
10.16
3.81
15˚
INCHES MILLIMETERS
2.54 BSC
7.62 BSC
0.100 BSC
0.300 BSC
A1
L
D1
e
21-324A
α8-PIN PLASTIC
DUAL-IN-LINE
PACKAGE
L
DIM
A
A1
B
C
D
E
e
H
h
L
α
MIN
0.053
0.004
0.014
0.007
0.189
0.150
0.228
0.010
0.016
0˚
MAX
0.069
0.010
0.019
0.010
0.197
0.157
0.244
0.020
0.050
8˚
MIN
1.35
0.10
0.35
0.19
4.80
3.80
5.80
0.25
0.40
0˚
MAX
1.75
0.25
0.49
0.25
5.00
4.00
6.20
0.50
1.27
8˚
INCHES MILLIMETERS
α
8-PIN PLASTIC
SMALL-OUTLINE
PACKAGE
HE
D
e
A
A1 C
h x 45˚
0.127mm
0.004in.
B
1.27 BSC0.050 BSC
21-325A
Maxim cannot assume responsibility for use of any circuitry other than circuitry entirely embodied in a Maxim product. No circuit patent licenses are
implied. Maxim reserves the right to change the circuitry and specifications without notice at any time.
16
__________________Maxim Integrated Products, 120 San Gabriel Drive, Sunnyvale, CA 94086 (408) 737-7600
© 1996 Maxim Integrated Products Printed USA is a registered trademark of Maxim Integrated Products.
MAX730A/MAX738A/MAX744A
5V, Step-Down,
Current-Mode PWM DC-DC Converters
___________________________________________Package Information (continued)
C
A
D
B1
B
DIM
A
B
B1
B2
C
D
E
E1
e
L
L1
Q
S
S1
α
MIN
–
0.014
0.038
0.023
0.008
–
0.220
0.290
0.125
0.150
0.015
–
0.005
0˚
MAX
0.200
0.023
0.065
0.045
0.015
0.405
0.310
0.320
0.200
–
0.060
0.055
–
15˚
MIN
–
0.36
0.97
0.58
0.20
–
5.59
7.37
3.18
3.81
0.38
–
0.13
0˚
MAX
5.08
0.58
1.65
1.14
0.38
10.29
7.87
8.13
5.08
–
1.52
1.40
–
15˚
INCHES MILLIMETERS
Q
L
S1
e
21-326D
8-PIN CERAMIC
DUAL-IN-LINE
PACKAGE
α
S
L1
E
E1 2.54 BSC0.100 BSC
B2
L
DIM
A
A1
B
C
D
E
e
H
h
L
α
MIN
0.093
0.004
0.014
0.009
0.398
0.291
0.394
0.010
0.016
0˚
MAX
0.104
0.012
0.019
0.013
0.413
0.299
0.419
0.030
0.050
8˚
MIN
2.35
0.10
0.35
0.23
10.10
7.40
10.00
0.25
0.40
0˚
MAX
2.65
0.30
0.49
0.32
10.50
7.60
10.65
0.75
1.27
8˚
INCHES MILLIMETERS
α
HE
D
e
A
A1 C
h x 45˚
0.127mm
0.004in.
B
1.27 BSC0.050 BSC
21-589B
16-PIN PLASTIC
SMALL-OUTLINE
(WIDE)
PACKAGE