MAXIM MAX744ACWE

19-0165; Rev 2; 1/96
5V, Step-Down,
Current-Mode PWM DC-DC Converters
________________________________Features
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 capability for inputs above 6V and has tighter oscillator frequency limits for low-noise (radio) applications. The
MAX730A accepts inputs between 5.2V and 11V and
delivers 450mA for inputs above 6V. Typical efficiencies 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 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. These regulators require only a
single inductor value to work in most applications, so
no inductor design is necessary.
♦ 750mA Load Currents (MAX738A/MAX744A)
The MAX730A/MAX738A/MAX744A also feature cycleby-cycle current limiting, overcurrent limiting, undervoltage lockout, and programmable soft-start protection.
___________________________Applications
Portable Instruments
Cellular Phones and Radios
Personal Communicators
♦ 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
PART
TEMP. RANGE
MAX730ACPA
0°C to +70°C
8 Plastic DIP
MAX730ACSA
MAX730AC/D
MAX730AEPA
MAX730AESA
MAX730AMJA
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
8 SO
Dice*
8 Plastic DIP
8 SO
8 CERDIP
Ordering Information continued at end of data sheet.
*Contact factory for dice specifications.
Distributed Power Systems
Computer Peripherals
__________Typical Operating Circuit
INPUT
6V TO 16V
_________________Pin Configurations
TOP VIEW
33µH
V+
68µF
LX
OUTPUT
5V
SHDN 1
MAX738A
MAX744A
ON/OFF
PIN-PACKAGE
SHDN
100µF
OUT
REF
2
SS 3
CC 4
REF
CC
SS
GND
MAX730A
MAX738A
MAX744A
8
V+
7
LX
6
GND
5
OUT
DIP
Pin Configurations continued on last page.
________________________________________________________________ Maxim Integrated Products
1
For free samples & the latest literature: http://www.maxim-ic.com, or phone 1-800-998-8800
MAX730A/MAX738A/MAX744A
__________________General Description
MAX730A/MAX738A/MAX744A
5V, Step-Down,
Current-Mode PWM DC-DC Converters
ABSOLUTE MAXIMUM RATINGS
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
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+ = 9V for the MAX730A, V+ = 12V for the MAX738A/MAX744A, ILOAD = 0mA, TA = TMIN to TMAX,
unless otherwise noted.)
PARAMETER
CONDITIONS
MAX730A
MIN TYP MAX
MAX738A
MIN TYP MAX
MAX744A
MIN TYP MAX
4.75 5.00
5.25
4.75 5.00
5.25
4.75 5.00
5.25
4.75 5.00
5.25
6.0
16.0
UNITS
0mA < ILOAD < 450mA,
MAX730AC
V+ = 6.0V
to 11.0V
0mA < ILOAD < 450mA,
MAX730AE
4.75 5.00
5.25
0mA < ILOAD < 300mA,
MAX730AM
0mA < ILOAD < 450mA,
MAX738AC/AE
Output Voltage
V+ = 6.0V
to 16.0V
0mA < ILOAD < 350mA,
MAX738AM
0mA < ILOAD < 500mA,
MAX744AC/AE
V
0mA < ILOAD < 375mA,
MAX744AM
V+ = 10.2V to 16.0V,
0mA < ILOAD < 750mA
V+ = 9.0V
to 16.0V
0mA < ILOAD < 750mA,
MAX744AC/AE
0mA < ILOAD < 600mA,
MAX744AM
Input Voltage
Range
Line Regulation
2
5.2
V+ = 5.2V to 11.0V
V+ = 6.0V to 16.0V
11.0
6.0
16.0
0.15
0.15
0.15
_______________________________________________________________________________________
V
%/V
5V, Step-Down,
Current-Mode PWM DC-DC Converters
(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
CONDITIONS
MAX730A
MIN TYP MAX
ILOAD = 0mA to 300mA
Load Regulation
MAX738A
MIN TYP MAX
MAX744A
MIN TYP MAX
0.0005
0.0005
90
90
87
87
0.0005
ILOAD = 0mA to 750mA
V+ = 9.0V, ILOAD = 300mA
Efficiency
92
V+ = 12V, ILOAD = 750mA
1.7
Supply Current
(includes switch
current)
3.0
1.7
3.0
1.7
%/mA
%
3.0
V+ = 6.0V
to 9.0V
MAX744AC/AE
MAX744AM
3.0
V+ = 9.0V
to 12.0V
MAX744AC/AE
3.0
MAX744AM
3.5
MAX744AC
4.0
MAX744AE
4.3
V+ = 12.0V
to 16.0V
1.2
MAX744AM
Standby Current
SHDN = 0V (Note 1)
Shutdown Input
Threshold
VIH
UNITS
2.5
mA
4.5
6.0
100.0
2.0
100.0
2.0
VIL
Shutdown Input
Leakage Current
Short-Circuit Current
6.0
100.0
2.0
0.25
0.25
0.25
1.0
1.0
1.0
1.5
4.7
6.0
1.5
5.7
1.5
6.0
µA
A
Undervoltage
Lockout
LX On Resistance
ILX = 500mA
0.5
0.5
0.5
Ω
LX Leakage Current
V+ = 12V, LX = 0V
1.0
1.0
1.0
µA
Reference Voltage
V+ = 12V, TA = +25°C
V+ falling
5.0
1.15 1.23
Reference Drift
1.30
1.15 1.23
50
130
Oscillator Frequency
V+ = 6.0V
to 16.0V
5.7
V
V+ rising
Compensation Pin
Impedance
5.2
µA
170
1.30
210
130
160
5.7
1.15 1.23
50
6.0
1.30
50
190
159.0 185.0 212.5
MAX744AM
159.0
7500
V
ppm/°C
MAX744AC/AE
7500
V
kHz
216.5
7500
Ω
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.
_______________________________________________________________________________________
3
MAX730A/MAX738A/MAX744A
ELECTRICAL CHARACTERISTICS (continued)
__________________________________________Typical Operating Characteristics
(Circuit of Figure 3, TA = +25°C, unless otherwise noted.)
MAX730A
EFFICIENCY vs. OUTPUT CURRENT
100
100
(NOTES 3, 6)
(NOTES 3, 6)
(NOTE 3)
90
V+ = 5.5V
80
V+ = 7V
V+ = 9V
70
V+ = 6V
80
V+ = 8V
V+ = 12V
60
200
400
600
800
OUTPUT CURRENT (mA)
V+ = 12.0V
0
MAXIMUM OUTPUT CURRENT vs.
SUPPLY VOLTAGE
200
400
600
800
OUTPUT CURRENT (mA)
0
1000
MAX730A
1000
QUIESCENT SUPPLY CURRENT (mA)
MAXIMUM OUTPUT CURRENT (mA)
(NOTES 3, 6)
MAX738A
400
600
800
OUTPUT CURRENT (mA)
1000
3.0
1400
MAX744A
200
QUIESCENT SUPPLY CURRENT
vs. TEMPERATURE
MAXIMUM OUTPUT CURRENT vs.
SUPPLY VOLTAGE, NO R1
(NOTES 3, 6)
1200
V+ = 16.0V
60
1000
1400
V+ = 9.0V
V+ = 16V
60
0
V+ = 6.0V
80
70
70
V+ = 11V
EFFICIENCY (%)
90
EFFICIENCY (%)
EFFICIENCY (%)
90
MAXIMUM OUTPUT CURRENT (mA)
MAX744A
EFFICIENCY vs. OUTPUT CURRENT
MAX738A
EFFICIENCY vs. OUTPUT CURRENT
100
1200
1000
800
MAX738A
MAX744A
600
MAX730A
400
2.5
MAX730A, V+ = 9.0V
MAX738A, V+ = 12.0V
MAX744A, V+ = 12.0V
2.0
1.5
1.0
0.5
(NOTES 4, 5)
800
4
8
6
10
12
14
0
-60 -40 -20 0
200
16
4
6
8
SUPPLY VOLTAGE (V)
10
12
14
16
SUPPLY VOLTAGE (V)
MAX738A/MAX744A
QUIESCENT SUPPLY CURRENT
vs. SUPPLY VOLTAGE
MAX738A/MAX744A
PEAK INDUCTOR CURRENT
vs. OUTPUT CURRENT
2.5
20 40 60 80 100 120 140 160
TEMPERATURE (°C)
STANDBY SUPPLY CURRENT
vs. TEMPERATURE
20
1000
PEAK INDUCTOR CURRENT (mA)
2.0
1.5
UNDERVOLTAGE
LOCKOUT HYSTERESIS
1.0
UNDERVOLTAGE
LOCKOUT ENABLED
0.5
4
2
4
6
8
600
400
V+ = 6.6V
V+ = 8.0V TO 16.0V
200
L1 = 100µH
C4 = 150µF
0
0
800
10
12
14
16
STANDBY SUPPLY CURRENT (µA)
(NOTES 4, 5)
QUIESCENT SUPPLY CURRENT (mA)
MAX730A/MAX738A/MAX744A
5V, Step-Down,
Current-Mode PWM DC-DC Converters
18
16
V+ = 16V
MAX738A/MAX744A
ONLY
14
12
10
V+ = 12V
MAX738A/MAX744A
ONLY
8
6
V+ = 9V
4
2
V+ = 6V
0
0
0
100 200
300 400 500
600 700 800
-60 -40 -20
0 20 40 60 80 100 120 140 160
_______________________________________________________________________________________
5V, Step-Down,
Current-Mode PWM DC-DC Converters
MAX730A
OSCILLATOR FREQUENCY
vs. TEMPERATURE
OSCILLATOR FREQUENCY vs.
SUPPLY VOLTAGE
220
240
(NOTE 3)
MAX730A
OSCILLATOR FREQUENCY (kHz)
OSCILLATOR FREQUENCY (kHz)
210
200
190
MAX744A
180
170
160
220
200
V+ = 11.0V
V+ = 5.5V
180
160
140
V+ = 7.0V
V+ = 9.0V
MAX738A
150
4
6
8
10
12
SUPPLY VOLTAGE (V)
14
0
-60 -40 -20 0
16
20 40 60 80 100 120 140 160
TEMPERATURE (°C)
MAX744A
OSCILLATOR FREQUENCY
vs. TEMPERATURE
MAX738A
OSCILLATOR FREQUENCY
vs. TEMPERATURE
210
200
(NOTE 4)
V+ = 6.0V
180
V+ = 16.0V
170
160
150
V+ = 12.0V
140
V+ = 9.0V
(NOTE 4)
OSCILLATOR FREQUENCY (kHz)
190
SUPPLY CURRENT (mA)
(NOTE 4)
200
V+ = 6.0V
V+ = 16.0V
190
V+ = 9.0V
180
V+ = 12.0V
130
120
-60 -40 -20 0
20 40 60 80 100 120 140 160
TEMPERATURE (°C)
170
-60 -40 -20 0
20 40 60 80 100 120 140 160
TEMPERATURE (°C)
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.
_______________________________________________________________________________________
5
MAX730A/MAX738A/MAX744A
____________________________Typical Operating Characteristics (continued)
(Circuit of Figure 3, TA = +25°C, unless otherwise noted.)
MAX730A/MAX738A/MAX744A
5V, Step-Down,
Current-Mode PWM DC-DC Converters
____________________________Typical Operating Characteristics (continued)
(Circuit of Figure 3, TA = +25°C, unless otherwise noted.)
MAX738A/MAX744A
SWITCHING WAVEFORMS,
DISCONTINUOUS CONDITION
MAX738A/MAX744A
SWITCHING WAVEFORMS,
CONTINUOUS CONDITION
12V
12V
A
A
0V
0V
200mA
200mA
B
0mA
0mA
C
B
C
2µs/div
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
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,
COUT = 390µF,
V+ = 12V, IOUT = 150µA
MAX738A/MAX744A LINE-TRANSIENT RESPONSE
MAX730A LINE-TRANSIENT RESPONSE
A
A
16V
B
11V
10.2V
B
6V
0V
0V
100ms/div
100ms/div
A: VOUT, 50mV/div, DC-COUPLED
B: V+, 5V/div, 6.0V TO 11.0V
A: VOUT, 50mV/div, DC-COUPLED
B: V+, 5V/div, 10.2V TO 16.0V
IOUT = 300mA
IOUT = 750mA
6
_______________________________________________________________________________________
5V, Step-Down,
Current-Mode PWM DC-DC Converters
MAX730A
LOAD-TRANSIENT RESPONSE
MAX738A/MAX744A
LOAD-TRANSIENT RESPONSE
A
A
750mA
300mA
B
B
50mA
20mA
50ms/div
50ms/div
A: VOUT, 50mV/div, DC-COUPLED
B: IOUT, 200mA/div, 20mA TO 300mA
A: VOUT, 50mV/div, DC-COUPLED
B: IOUT, 500mA/div, 50mA TO 750mA
V+ = 9V
V+ = 12V
______________________________________________________________Pin Description
PIN
8-PIN
DIP/SO
16-PIN
WIDE SO
NAME
FUNCTION
1
2
SHDN
2
3
REF
3
7
SS
Soft-Start. Capacitor between SS and GND provides soft-start and short-circuit protection.
510kΩ resistor from SS to SHDN provides current boost.
4
8
CC
Compensation Capacitor Input externally compensates the outer feedback loop.
Connect to OUT with a 330pF capacitor.
Shutdown—active low. Ground to power-down chip, tie to V+ for normal operation.
Output voltage falls to 0V when SHDN is low.
Reference-Voltage Output (+1.23V) supplies up to 100µA for extended loads.
Bypass to GND with a capacitor that does not exceed 0.047µF.
5
9
OUT
Output Voltage Sense Input provides regulation feedback sensing. Connect to +5V output.
6
10, 11
GND
Ground pins are internally connected. Connect both pins to ground.
7
12, 13, 14
LX
Drain of internal P-channel power MOSFET.
8
1, 15, 16
V+
Supply-Voltage Input. Bypass to GND with 1µF ceramic and large-value electrolytic capacitors in parallel. The 1µF capacitor must be as close to V+ and GND pins as possible.
4, 5, 6
N.C.
No Connect—no internal connections to these pins.
_______________________________________________________________________________________
7
MAX730A/MAX738A/MAX744A
____________________________Typical Operating Characteristics (continued)
(Circuit of Figure 3, TA = +25°C, unless otherwise noted.)
MAX730A/MAX738A/MAX744A
5V, Step-Down,
Current-Mode PWM DC-DC Converters
_________________Detailed Description
The MAX730A/MAX738A/MAX744A switch-mode regulators use a current-mode pulse-width-modulation
(PWM) control system coupled with a simple step-down
(buck) regulator topography. They convert an unregulated 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-bycycle 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 current-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-bycycle current limiting, truncating the power transistor ontime 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 connected to the soft-start (SS) pin to ensure an orderly
power-up. Typical values are 0.1µF and 510kΩ. SS controls 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 current-limit threshold. The 510kΩ resistor sets the SS
clamp at a value high enough to maintain regulation,
even at currents exceeding 1A. This resistor is not necessary for lower-current loads. Refer to the Maximum
Output Current vs. Supply Voltage graph in the Typical
Operating Characteristics. Table 1 lists timing characteristics for selected capacitor values and circuit conditions.
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 current 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
8
for overcurrent protection to function properly. A typical
value is 0.1µF.
Undervoltage Lockout
The MAX738A/MAX744A’s undervoltage-lockout feature monitors the supply voltage at V+, and allows
operation to start when V+ rises above 5.7V (6V guaranteed). 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 operation 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 discharges the SS capacitor 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 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 standby 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-/DiscontinuousConduction 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
MAX730A/MAX738A/MAX744A 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 continuous-conduction mode (CCM), the inductor current never decays to
zero, which is typically more efficient than DCM. CCM
allows the MAX730A/ MAX738A/MAX744A to deliver maximum 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
MAX730A/MAX738A/MAX744A
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
None
11
9
0
150
100
100
8
34
18
134
28
270
66
1263
None
9
150
390
39
147
280
1275
None
9
150
680
40
152
285
1280
MAX738A/MAX744A CIRCUIT CONDITIONS
R1 (kΩ)
V+ (V)
SOFT-START TIME (ms) vs. C1 (µF)
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
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 operates 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 communications systems. The Typical Operating Characteristics
graphs indicate oscillator frequency stability over temperature 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
_______________________________________________________________________________________
9
MAX730A/MAX738A/MAX744A
5V, Step-Down,
Current-Mode PWM DC-DC Converters
VIN = +6.0V TO +16.0V
SHDN
C2
C3*
1µF
V+
OVERCURRENT COMPARATOR
SLOPE COMPENSATION
BIAS
GEN
Σ
OUT
C5
330pF
RAMP
GEN
RSENSE
ERROR AMP
F/F
CC
R
Q
S
1.23V
BANDGAP
R1
510k
CURRENT
SENSE AMP
PWM
COMPARATOR
D1
1N5817
REF
OSC
C6
0.01µF
1M
±35%
L1
LX
SS CLAMP
SS
VOUT =
+5V
C4*
MAX730A
MAX738A
MAX744A
UNDERVOLTAGE
LOCKOUT
C1
0.1µF
VUVLO
GND
*SEE TABLE 2 FOR COMPONENT VALUES AND SUPPLIERS
Figure 1. Detailed Block Diagram with External Components
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 surfacemount inductors have nearly equivalent efficiencies to
the larger through-hole inductors.
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 suggested capacitor suppliers.
Output Filter Capacitor Selection
Other Components
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, minimize the output filter capacitor’s ESR to maintain AC
stability. The capacitor’s ESR should be less than
0.25Ω to keep the output ripple less than 50mVp-p over
the entire current range (using a 100µH inductor).
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 applications, the 510kΩ resistor may be omitted (see the
Maximum Output Current vs. Supply Voltage graph (R1
removed) in the Typical Operating Characteristics).
10
______________________________________________________________________________________
5V, Step-Down,
Current-Mode PWM DC-DC Converters
Production
Method
MAX730AC/MAX738AC/MAX744AC
Commercial Temp. Range
Inductors
L1 = 33µH to 100µH
Surface
Mount
Sumida (708) 956-0666
CD54-101KC (MAX730AC)
CD105-101KC
(MAX738AC/MAX744AC)
Coiltronics (407) 241-7876
CTX100 series
MAX730AE/M, MAX738AE/M, MAX744AE/M
Wide Temp. Range
Capacitors
Inductors
Capacitors
L1 = 33µH
C3 = 68µF, 16V
C4 = 100µF, 6.3V
Sumida (708) 956-0666
CD54-330N (MAX730AC)
CD105-330N
(MAX738AE/M, MAX744AE/M)
Matsuo (714) 969-2491
267 series
Sprague (603) 224-1961
595D/293D series
C3 = 68µF, 16V
C4 = 100µF, 6.3V
Matsuo (714) 969-2491
267 series
Sprague (603) 224-1961
595D/293D series
Coiltronics (407) 241-7876
CTX50 series
C3 = 150µF, 16V
C4 = 220µF, 10V
L1 = 33µH to 100µH
Miniature
ThroughHole
Sumida (708) 956-0666
RCH654-101K (MAX730A)
RCH895-101K
(MAX738A/MAX744A)
L1 = 33µH
Nichicon (708) 843-7500
PL series
Low-ESR electrolytics
Sumida (708) 956-0666
RCH654-330M (MAX730A)
RCH895-330M
(MAX738A/MAX744A)
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)
C3 = 150µF, 16V
C4 = 390µF, 6.3V
L1 = 100µH
Low-Cost
ThroughHole
C3 = 150µF, 16V
C4 = 150µF, 16V or
390µF, 6.3V
Maxim
MAXL001
100µH iron-power toroid
Renco (516) 586-5566
RL1284-100
Maxim
MAXC001
150µF, low-ESR
electrolytic
United Chemicon
(708) 843-7500
Printed Circuit Layouts
Output-Ripple Filtering
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 output capacitor as close to the OUT and GND pins as possible. The traces connecting the input and output filter
capacitors and the catch diode must be short to minimize 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.
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 resistance should be minimized so the voltage drop across
it is not excessive.
______________________________________________________________________________________
11
MAX730A/MAX738A/MAX744A
Table 2. Component Values and Suppliers
MAX730A/MAX738A/MAX744A
5V, Step-Down,
Current-Mode PWM DC-DC Converters
FROM SHDN
R1
510k
SS CLAMP
SS
1M
±35%
C1
1.23V
MAX730A
MAX738A
MAX744A
Figure 2. Block Diagram of Soft-Start Circuitry
MAX730A +5.2V TO +11.0V
MAX738A/MAX744A +6.0V TO +16.0V
OPTIONAL LOWPASS OUTPUT FILTER
C2
1µF
L2
25µH
C3*
8
1
SHDN
OUTPUT
V+
LX
7
D1
1N5817
MAX730A
MAX738A OUT 5
MAX744A
R1
510k
3
C1
0.1µF
SS
GND
6
CC
4
FILTER
OUTPUT
C7
2.2µF
L1*
OUTPUT
+5V
C5
330pF
C4*
REF
2
PART
INPUT SUPPLY RANGE (V)
GUARANTEED OUTPUT CURRENT AT 5V (mA)
MAX730A
6.0 to 11.0
450
6.0 to 16.0
450
10.2 to 16.0
750
6.0 to 9.0
500
9.0 to 16.0
750
MAX738A
C6
0.01µF
MAX744A
*SEE TABLE 2 FOR COMPONENT VALUES AND SUPPLIERS.
NOTE: PIN NUMBERS REFER TO 8-PIN PACKAGES.
Figure 3. Standard +5V Step-Down Application Circuit
12
______________________________________________________________________________________
5V, Step-Down,
Current-Mode PWM DC-DC Converters
MAX730A/MAX738A/MAX744A
MAX730 EVALUATION KIT
Figure 4. DIP PC Layout, Through-Hole Component Placement
Diagram (1x scale)
Figure 5. DIP PC Layout, Component Side (1x scale)
Figure 6. DIP PC Layout, Solder Side (1x scale)
Figure 7. DIP PC Layout, Drill Guide (1x scale)
______________________________________________________________________________________
13
MAX730A/MAX738A/MAX744A
5V, Step-Down,
Current-Mode PWM DC-DC Converters
____Pin Configurations (continued)
__Ordering Information (continued)
TOP VIEW
SHDN
1
REF
2
MAX730A
SS 3
CC 4
8
V+
7
LX
6
GND
5
OUT
SO
V+ 1
16 V+
SHDN 2
15 V+
REF 3
14 LX
MAX738A
MAX744A
N.C. 4
N.C. 5
PART
TEMP. RANGE
PIN-PACKAGE
MAX738ACPA
0°C to +70°C
8 Plastic DIP
MAX738ACWE
MAX738AC/D
MAX738AEPA
MAX738AEWE
MAX738AMJA
MAX744ACPA
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
0°C to +70°C
16 Wide SO
Dice*
8 Plastic DIP
16 Wide SO
8 CERDIP
8 Plastic DIP
MAX744ACWE
0°C to +70°C
MAX744AC/D
0°C to +70°C
MAX744AEPA
-40°C to +85°C
MAX744AEWE
-40°C to +85°C
MAX744AMJA
-55°C to +125°C
*Contact factory for dice specifications.
13 LX
16 Wide SO
Dice*
8 Plastic DIP
16 Wide SO
8 CERDIP
12 LX
N.C. 6
11 GND
SS 7
10 GND
9
CC 8
OUT
Wide SO
__________________________________________________________Chip Topographies
MAX738A/MAX744A
MAX730A
SHDN
SHDN
V+
V+
REF
REF
LX
LX
0.116"
(2.946mm)
0.131"
(3.327mm)
SS
GND
GND
SS
CC
0.072"
(1.828mm)
OUT
TRANSISTOR COUNT: 274 (MAX730A)
286 (MAX738A/MAX744A);
SUBSTRATE CONNECTED TO V+.
14
OUT
CC
0.116"
(2.946mm)
______________________________________________________________________________________
5V, Step-Down,
Current-Mode PWM DC-DC Converters
DIM
D1
A
A1
A2
A3
B
B1
C
D
D1
E
E1
e
eA
eB
L
α
E
E1
D
A3
A
A2
L
A1
INCHES
MAX
MIN
0.200
–
–
0.015
0.175
0.125
0.080
0.055
0.022
0.016
0.065
0.050
0.012
0.008
0.390
0.348
0.035
0.005
0.325
0.300
0.280
0.240
0.100 BSC
0.300 BSC
0.400
–
0.150
0.115
15˚
0˚
MILLIMETERS
MIN
MAX
–
5.08
0.38
–
3.18
4.45
1.40
2.03
0.41
0.56
1.27
1.65
0.20
0.30
8.84
9.91
0.13
0.89
7.62
8.26
6.10
7.11
2.54 BSC
7.62 BSC
–
10.16
2.92
3.81
0˚
15˚
21-324A
α
8-PIN PLASTIC
DUAL-IN-LINE
PACKAGE
C
e
B1
eA
B
eB
DIM
E
A
A1
B
C
D
E
e
H
h
L
α
H
INCHES
MAX
MIN
0.069
0.053
0.010
0.004
0.019
0.014
0.010
0.007
0.197
0.189
0.157
0.150
0.050 BSC
0.244
0.228
0.020
0.010
0.050
0.016
8˚
0˚
MILLIMETERS
MIN
MAX
1.35
1.75
0.10
0.25
0.35
0.49
0.19
0.25
4.80
5.00
3.80
4.00
1.27 BSC
5.80
6.20
0.25
0.50
0.40
1.27
0˚
8˚
21-325A
h x 45˚
D
α
A
0.127mm
0.004in.
e
A1
C
L
8-PIN PLASTIC
SMALL-OUTLINE
PACKAGE
B
______________________________________________________________________________________
15
MAX730A/MAX738A/MAX744A
________________________________________________________Package Information
MAX730A/MAX738A/MAX744A
5V, Step-Down,
Current-Mode PWM DC-DC Converters
___________________________________________Package Information (continued)
DIM
E1
D
E
B2
A
A
B
B1
B2
C
D
E
E1
e
L
L1
Q
S
S1
α
S
S1
INCHES
MAX
MIN
0.200
–
0.023
0.014
0.065
0.038
0.045
0.023
0.015
0.008
0.405
–
0.310
0.220
0.320
0.290
0.100 BSC
0.200
0.125
–
0.150
0.060
0.015
0.055
–
–
0.005
15˚
0˚
MILLIMETERS
MIN
MAX
–
5.08
0.36
0.58
0.97
1.65
0.58
1.14
0.20
0.38
–
10.29
5.59
7.87
7.37
8.13
2.54 BSC
3.18
5.08
3.81
–
0.38
1.52
–
1.40
0.13
–
0˚
15˚
21-326D
α
Q
L
L1
e
8-PIN CERAMIC
DUAL-IN-LINE
PACKAGE
C
B1
B
DIM
E
A
A1
B
C
D
E
e
H
h
L
α
H
INCHES
MAX
MIN
0.104
0.093
0.012
0.004
0.019
0.014
0.013
0.009
0.413
0.398
0.299
0.291
0.050 BSC
0.419
0.394
0.030
0.010
0.050
0.016
8˚
0˚
MILLIMETERS
MIN
MAX
2.35
2.65
0.10
0.30
0.35
0.49
0.23
0.32
10.10
10.50
7.40
7.60
1.27 BSC
10.00
10.65
0.25
0.75
0.40
1.27
0˚
8˚
21-589B
h x 45˚
D
α
A
0.127mm
0.004in.
e
B
A1
C
L
16-PIN PLASTIC
SMALL-OUTLINE
(WIDE)
PACKAGE
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.