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MAX730ACPA+ |MAX730ACPAMAXIMN/a354avai5V, Step-Down, Current-Mode PWM DC-DC Converters
MAX730ACSA+ |MAX730ACSAMAXIMN/a4167avai5V, Step-Down, Current-Mode PWM DC-DC Converters
MAX738ACPA+ |MAX738ACPAMAXIMN/a3300avai5V, Step-Down, Current-Mode PWM DC-DC Converters
MAX744ACPA+ |MAX744ACPAMAXIMN/a1000avai5V, Step-Down, Current-Mode PWM DC-DC Converters
MAX744ACWE+ |MAX744ACWEMAXIMN/a13avai5V, Step-Down, Current-Mode PWM DC-DC Converters
MAX744AEWE+TMAXIMN/a25avai5V, Step-Down, Current-Mode PWM DC-DC Converters


MAX730ACSA+ ,5V, Step-Down, Current-Mode PWM DC-DC ConvertersFeaturesThe MAX730A/MAX738A/MAX744A are 5V-output♦ 750mA Load Currents (MAX738A/MAX744A)CMOS, step- ..
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MB501 , TECHNICAL SPECIFICATIONS OF SINGLE-PHASE SILICON BRIDGE RECTIFIER
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MAX730ACPA+-MAX730ACSA+-MAX738ACPA+-MAX744ACPA+-MAX744ACWE+-MAX744AEWE+T
5V, Step-Down, Current-Mode PWM DC-DC Converters
________________General DescriptionThe 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_______________________________Feature750mA Load Currents (MAX738A/MAX744A)High-Frequency, Current-Mode PWM159kHz to 212.5kHz Guaranteed Oscillator
Frequency Limits (MAX744A)
85% to 96% Efficiencies1.7mA Quiescent Current6μA Shutdown Supply CurrentSingle Preselected Inductor Value,
No Component Design Required
Overcurrent, Soft-Start, and Undervoltage
Lockout Protection
Cycle-by-Cycle Current Limiting8-Pin DIP/SO Packages (MAX730A)________________Ordering Information
Ordering Information continued at end of data sheet.

*Contact factory for dice specifications.V, Step-Dow
Current-Mode PWM DC-DC Converte

TOP VIEW
GND
OUTCC
REF
MAX730A
MAX738A
MAX744A
DIP

SHDN
Pin Configurations continued on last page.
_________________Pin Configurations

MAX738A
MAX744A
INPUT
6V TO 16V
LX
OUT
GNDSS
REF
SHDNON/OFF
33μHOUTPUT
100μF
68μF
__________Typical Operating Circuit

19-0165; Rev 2; 1/96
PARTTEMP. RANGEPIN-PACKAGE
MAX730ACPA
0°C to +70°C8 Plastic DIP
MAX730ACSA0°C to +70°C8 SO
MAX730AC/D0°C to +70°CDice*
MAX730AEPA8 Plastic DIP
MAX730AESA-40°C to +85°C8 SO
-40°C to +85°C
MAX730AMJA-55°C to +125°C8 CERDIP
V, Step-Down,Current-Mode PWM DC-DC Converters
ABSOLUTE MAXIMUM RATINGS
ELECTRICAL CHARACTERISTICS

(Circuit of Figure 3, V+ = 9V for the MAX730A, V+ = 12V for the MAX738A/MAX744A, ILOAD= 0mA, TA= TMINto 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.
PARAMETERMAX730A
MINTYPMAXUNITS

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
MINTYPMAX

MAX744A
MINTYPMAX
Output VoltageV
V+ = 9.0V
to 16.0V
6.016.06.016.05.211.0V
V+ = 5.2V to 11.0V0.15
V+ = 6.0V to 16.0V0.150.15%/VLine 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
V, Step-Down,Current-Mode PWM DC-DC Converters
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= TMINto TMAX,
unless otherwise noted.)
PARAMETER

ILOAD= 0mA to 300mA
MAX730A
MINTYPMAX

Supply Current
(includes switch
current)
ILOAD= 0mA to 750mA
UNITS

V+ = 9.0V, ILOAD= 300mA
MAX738A
MINTYPMAX

MAX744AE
ILX= 500mA
6.0100.06.0100.06.0100.0μAStandby Current
VIH
LX On Resistance
MAX744AC/AE
VIL
MAX744A
MINTYPMAX

0.250.250.25V
Shutdown Input
Threshold
%/mA
Shutdown Input
Leakage Current
V+ = 12V, ILOAD= 750mA
Load Regulation0.0005
SHDN= 0V (Note 1)
MAX744AC/AE1.22.5
V+ = 12V, LX = 0V
MAX744AM
V+ = 6.0V
to 9.0V
MAX744AC/AE3.0
1.0μA
Reference Drift
MAX744AM
MAX744AM
V+ = 9.0V
to 12.0V
MAX744AC4.050
LX Leakage Current
CONDITIONSShort-Circuit Current
V+ rising
V+ falling5.05.7V
kHz
Undervoltage
Lockout%Efficiency92
V+ = 6.0V
to 16.0V
V+ = 12V, TA= +25°CReference Voltage1.151.231.301.151.231.301.151.231.30V
ppm/°C
Oscillator Frequency
750075007500ΩCompensation Pin
Impedance
V+ = 12.0V
to 16.0V
MAX744AM
OUTPUT CURRENT (mA)
(%
MAX730A
EFFICIENCY vs. OUTPUT CURRENT

V+ = 5.5V
V+ = 7V
V+ = 9V
V+ = 11V
(NOTES 3, 6)
OUTPUT CURRENT (mA)
(%
MAX738A
EFFICIENCY vs. OUTPUT CURRENT

V+ = 6V
V+ = 8V
V+ = 12V
V+ = 16V
(NOTES 3, 6)
(m
MAX738A/MAX744A
QUIESCENT SUPPLY CURRENT
vs. SUPPLY VOLTAGE

UNDERVOLTAGE
LOCKOUT HYSTERESIS
UNDERVOLTAGE
LOCKOUT ENABLED
IN
(m
MAX738A/MAX744A
PEAK INDUCTOR CURRENT
vs. OUTPUT CURRENT

L1 = 100μH
C4 = 150μF
V+ = 6.6V V+ = 8.0V TO 16.0VV, Step-Down,
Current-Mode PWM DC-DC Converters
__________________________________________Typical Operating Characteristics

(Circuit of Figure 3, TA = +25°C, unless otherwise noted.)
OUTPUT CURRENT (mA)
(%
MAX744A
EFFICIENCY vs. OUTPUT CURRENT

V+ = 6.0V
V+ = 9.0V
V+ = 12.0V
V+ = 16.0V
(NOTE 3)

STANDBY SUPPLY CURRENT
vs. TEMPERATURE

V+ = 16V
MAX738A/MAX744A
ONLY
V+ = 9V
V+ = 6V
(NOTES 4, 5)
V+ = 12V
MAX738A/MAX744A
ONLY
TEMPERATURE (°C)
(m
QUIESCENT SUPPLY CURRENT
vs. TEMPERATURE

MAX730A, V+ = 9.0V
MAX738A, V+ = 12.0V
MAX744A, V+ = 12.0V
(NOTES 4, 5)
SUPPLY VOLTAGE (V)
(m
MAXIMUM OUTPUT CURRENT vs.
SUPPLY VOLTAGE

MAX738A
MAX730A
MAX744A
(NOTES 3, 6)
SUPPLY VOLTAGE (V)
(m
MAXIMUM OUTPUT CURRENT vs.
SUPPLY VOLTAGE, NO R1

(NOTES 3, 6)
MAX738A
MAX730A
MAX744A
V, Step-Down,Current-Mode PWM DC-DC Converters
____________________________Typical Operating Characteristics (continued)

(Circuit of Figure 3, TA = +25°C, unless otherwise noted.)681014
SUPPLY VOLTAGE (V)
(k
OSCILLATOR FREQUENCY vs.
SUPPLY VOLTAGE
16
MAX744A
MAX738A
MAX730A
(NOTE 3)220
TEMPERATURE (°C)
(k
MAX744A
OSCILLATOR FREQUENCY
vs. TEMPERATURE

V+ = 6.0V
V+ = 16.0V
V+ = 9.0V
V+ = 12.0V
(NOTE 4)
TEMPERATURE (°C)
(m
MAX738A
OSCILLATOR FREQUENCY
vs. TEMPERATURE

V+ = 6.0V
V+ = 16.0V
V+ = 12.0V
V+ = 9.0V
(NOTE 4)
TEMPERATURE (°C)
(kH
MAX730A
OSCILLATOR FREQUENCY
vs. TEMPERATURE

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 TA> +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.
V, Step-Down,Current-Mode PWM DC-DC Converters
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
200mA
0mA
200mA
0mA
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 16.0VOUT= 750mA
11V
16V
10.2V
____________________________Typical Operating Characteristics (continued)

(Circuit of Figure 3, TA = +25°C, unless otherwise noted.)
12V
V, Step-Down,Current-Mode PWM DC-DC Converters
NAMEFUNCTION
SHDNShutdown—active low. Ground to power-down chip, tie to V+ for normal operation.
Output voltage falls to 0V when SHDNis low.REFSSSoft-Start. Capacitor between SSand GND provides soft-start and short-circuit protection.
510kΩresistor from SS to SHDNprovides current boost.CCCompensation Capacitor Input externally compensates the outer feedback loop.
Connect to OUT with a 330pF capacitor.OUTOutput Voltage Sense Input provides regulation feedback sensing. Connect to +5V output.GNDGround pins are internally connected. Connect both pins to ground.LXDrain of internal P-channel power MOSFET.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 GNDpins 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
____________________________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
PIN
_________________Detailed DescriptionThe 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 SHDNat 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 SHDNto 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.V, Step-Down,
Current-Mode PWM DC-DC Converters
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