MAX744ACWE+T [MAXIM]
Switching Regulator, Current-mode, 2A, 212.5kHz Switching Freq-Max, CMOS, PDSO16, PLASTIC, SOP-16;
| 型号： | MAX744ACWE+T |
| 厂家： | 
MAXIM INTEGRATED PRODUCTS |
| 描述： | Switching Regulator, Current-mode, 2A, 212.5kHz Switching Freq-Max, CMOS, PDSO16, PLASTIC, SOP-16 转换器 |
| 文件： | 总16页 (文件大小：230K) |
| 中文： | 中文翻译 | 下载： | 下载PDF数据表文档文件 |
19-0165; Rev 2; 1/96
5 V, S t e p -Do w n ,
Cu rre n t -Mo d e P WM DC-DC Co n ve rt e rs
038/MX74A
__________________Ge n e ra l De s c rip t io n
________________________________Fe a t u re s
♦ 750mA Load Currents (MAX738A/MAX744A)
♦ High-Frequency, Current-Mode PWM
The MAX730A/MAX738A/MAX744A a re 5V-outp ut
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-
c ie s a re 85% to 96%. Quie s c e nt s up p ly c urre nt is
1.7mA and only 6µA in shutdown.
♦ 159kHz to 212.5kHz Guaranteed Oscillator
Frequency Limits (MAX744A)
♦ 85% to 96% Efficiencies
♦ 1.7mA Quiescent Current
♦ 6µA Shutdown Supply Current
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.
♦ 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)
_________________Ord e rin g In fo rm a t io n
The MAX730A/MAX738A/MAX744A also feature cycle-
by-cycle current limiting, overcurrent limiting, undervolt-
age lockout, and programmable soft-start protection.
PART
TEMP. RANGE
0°C to +70°C
PIN-PACKAGE
8 Plastic DIP
8 SO
MAX730ACPA
MAX730ACSA
MAX730AC/D
MAX730AEPA
MAX730AESA
MAX730AMJA
0°C to +70°C
___________________________Ap p lic a t io n s
0°C to +70°C
Dice*
Portable Instruments
-40°C to +85°C
-40°C to +85°C
-55°C to +125°C
8 Plastic DIP
8 SO
Cellular Phones and Radios
Personal Communicators
Distributed Power Systems
Computer Peripherals
8 CERDIP
Ordering Information continued at end of data sheet.
*Contact factory for dice specifications.
_________________P in Co n fig u ra t io n s
__________Typ ic a l Op e ra t in g Circ u it
INPUT
6V TO 16V
TOP VIEW
OUTPUT
5V
33µH
V+
68µF
LX
SHDN
REF
SS
V+
1
2
3
4
8
7
6
5
100µF
MAX738A
MAX744A
LX
MAX730A
MAX738A
MAX744A
ON/OFF
SHDN
REF
OUT
CC
GND
OUT
CC
DIP
SS
GND
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
5 V, S t e p -Do w n ,
Cu rre n t -Mo d e P WM DC-DC Co n ve rt e rs
ABSOLUTE MAXIMUM RATINGS
Pin Voltages
Operating Temperature Ranges:
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)
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
Peak Switch Current (I ) ........................................................2A
LX
Reference Current (I ) ...................................................2.5mA
REF
Continuous Power Dissipation (T = +70°C)
A
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
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, I
unless otherwise noted.)
= 0mA, T = T
to T
,
LOAD
A
MIN
MAX
MAX730A
MAX738A
MAX744A
PARAMETER
CONDITIONS
0mA < I
UNITS
MIN TYP MAX MIN TYP MAX MIN TYP MAX
< 450mA,
< 450mA,
< 300mA,
< 450mA,
LOAD
MAX730AC
V+ = 6.0V
to 11.0V
0mA < I
LOAD
4.75 5.00 5.25
MAX730AE
0mA < I
LOAD
038/MX74A
MAX730AM
0mA < I
LOAD
MAX738AC/AE
0mA < I
MAX738AM
< 350mA,
< 500mA,
LOAD
V+ = 6.0V
to 16.0V
4.75 5.00 5.25
4.75 5.00 5.25
Output Voltage
V
0mA < I
LOAD
MAX744AC/AE
0mA < I
< 375mA,
LOAD
MAX744AM
V+ = 10.2V to 16.0V,
0mA < I < 750mA
4.75 5.00 5.25
LOAD
0mA < I
< 750mA,
LOAD
MAX744AC/AE
V+ = 9.0V
to 16.0V
4.75 5.00 5.25
0mA < I < 600mA,
LOAD
MAX744AM
Input Voltage
Range
5.2
11.0
6.0
16.0
6.0
16.0
V
V+ = 5.2V to 11.0V
V+ = 6.0V to 16.0V
0.15
Line Regulation
%/V
0.15
0.15
2
_______________________________________________________________________________________
5 V, S t e p -Do w n ,
Cu rre n t -Mo d e P WM DC-DC Co n ve rt e rs
038/MX74A
ELECTRICAL CHARACTERISTICS (continued)
(Circuit of Figure 3, V+ = 9V for the MAX730A, V+ = 12V for the MAX738A/MAX744A, I
unless otherwise noted.)
= 0mA, T = T
to T
,
LOAD
A
MIN
MAX
MAX730A
MAX738A
MAX744A
PARAMETER
CONDITIONS
UNITS
MIN TYP MAX MIN TYP MAX MIN TYP MAX
I
= 0mA to 300mA
= 0mA to 750mA
0.0005
LOAD
Load Regulation
%/mA
I
0.0005
90
0.0005
90
LOAD
V+ = 9.0V, I
= 300mA
= 750mA
92
LOAD
Efficiency
%
V+ = 12V, I
87
87
LOAD
1.7
3.0
1.7
3.0
1.7
3.0
2.5
3.0
3.0
3.5
4.0
4.3
4.5
MAX744AC/AE
MAX744AM
MAX744AC/AE
MAX744AM
MAX744AC
1.2
V+ = 6.0V
to 9.0V
Supply Current
(includes switch
current)
V+ = 9.0V
to 12.0V
mA
V+ = 12.0V
to 16.0V
MAX744AE
MAX744AM
Standby Current
SHDN = 0V (Note 1)
6.0 100.0
6.0 100.0
6.0 100.0
µA
V
V
IH
2.0
2.0
2.0
5.0
Shutdown Input
Threshold
V
IL
0.25
1.0
0.25
1.0
0.25
1.0
Shutdown Input
Leakage Current
µA
A
Short-Circuit Current
1.5
1.5
1.5
V+ rising
V+ falling
4.7
5.2
5.7
6.0
5.7
6.0
5.7
Undervoltage
Lockout
V
LX On Resistance
LX Leakage Current
Reference Voltage
Reference Drift
I
= 500mA
0.5
1.0
0.5
1.0
0.5
1.0
Ω
µA
LX
V+ = 12V, LX = 0V
V+ = 12V, T = +25°C
1.15 1.23 1.30
50
1.15 1.23 1.30
50
1.15 1.23 1.30
50
V
A
ppm/°C
130 170 210
130 160 190
Oscillator Frequency
MAX744AC/AE
MAX744AM
159.0 185.0 212.5
kHz
V+ = 6.0V
to 16.0V
159.0
216.5
Compensation Pin
Impedance
7500
7500
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
5 V, S t e p -Do w n ,
Cu rre n t -Mo d e P WM DC-DC Co n ve rt e rs
__________________________________________Typ ic a l Op e ra t in g Ch a ra c t e ris t ic s
(Circuit of Figure 3, T = +25°C, unless otherwise noted.)
A
MAX744A
EFFICIENCY vs. OUTPUT CURRENT
MAX730A
EFFICIENCY vs. OUTPUT CURRENT
MAX738A
EFFICIENCY vs. OUTPUT CURRENT
100
90
100
90
100
90
(NOTES 3, 6)
(NOTE 3)
(NOTES 3, 6)
V+ = 6.0V
V+ = 5.5V
V+ = 6V
80
70
60
80
70
60
80
70
60
V+ = 9.0V
V+ = 7V
V+ = 9V
V+ = 8V
V+ = 12.0V
V+ = 12V
V+ = 16.0V
V+ = 11V
V+ = 16V
0
200
400
600
800
1000
0
200
400
600
800
1000
0
200
400
600
800
1000
OUTPUT CURRENT (mA)
OUTPUT CURRENT (mA)
OUTPUT CURRENT (mA)
QUIESCENT SUPPLY CURRENT
vs. TEMPERATURE
MAXIMUM OUTPUT CURRENT vs.
SUPPLY VOLTAGE
MAXIMUM OUTPUT CURRENT vs.
SUPPLY VOLTAGE, NO R1
1400
3.0
1400
(NOTES 3, 6)
MAX744A
(NOTES 3, 6)
MAX730A, V+ = 9.0V
MAX738A, V+ = 12.0V
MAX744A, V+ = 12.0V
1200
1000
800
2.5
2.0
1.5
1.0
0.5
1200
1000
800
MAX738A
MAX738A
MAX744A
038/MX74A
MAX730A
600
MAX730A
6
400
(NOTES 4, 5)
0
200
4
6
8
10
12
14
16
-60 -40 -20
0
20 40 60 80 100 120 140 160
TEMPERATURE (°C)
4
8
10
12
14
16
SUPPLY VOLTAGE (V)
SUPPLY VOLTAGE (V)
MAX738A/MAX744A
QUIESCENT SUPPLY CURRENT
vs. SUPPLY VOLTAGE
MAX738A/MAX744A
PEAK INDUCTOR CURRENT
vs. OUTPUT CURRENT
STANDBY SUPPLY CURRENT
vs. TEMPERATURE
2.5
20
1000
800
(NOTES 4, 5)
V+ = 16V
18
16
14
12
MAX738A/MAX744A
ONLY
2.0
1.5
1.0
0.5
0
V+ = 12V
MAX738A/MAX744A
ONLY
600
10
8
UNDERVOLTAGE
LOCKOUT HYSTERESIS
V+ = 8.0V TO 16.0V
400
200
0
V+ = 6.6V
6
4
2
0
V+ = 9V
V+ = 6V
-60 -40 -20 0 20 40 60 80 100 120 140 160
UNDERVOLTAGE
LOCKOUT ENABLED
L1 = 100µH
C4 = 150µF
12 14 16
0
2
4
6
8
10
600 700 800
0
100 200 300 400 500
4
_______________________________________________________________________________________
5 V, S t e p -Do w n ,
Cu rre n t -Mo d e P WM DC-DC Co n ve rt e rs
038/MX74A
____________________________Typ ic a l Op e ra t in g Ch a ra c t e ris t ic s (c o n t in u e d )
(Circuit of Figure 3, T = +25°C, unless otherwise noted.)
A
MAX730A
OSCILLATOR FREQUENCY
vs. TEMPERATURE
OSCILLATOR FREQUENCY vs.
SUPPLY VOLTAGE
220
240
220
(NOTE 3)
(NOTE 4)
V+ = 11.0V
210
MAX730A
200
200
180
160
140
0
V+ = 5.5V
190
MAX744A
180
170
V+ = 7.0V
V+ = 9.0V
160
MAX738A
150
4
6
8
10
12
14
16
-60 -40 -20
0
20 40 60 80 100 120 140 160
TEMPERATURE (°C)
SUPPLY VOLTAGE (V)
MAX744A
MAX738A
OSCILLATOR FREQUENCY
vs. TEMPERATURE
OSCILLATOR FREQUENCY
vs. TEMPERATURE
210
200
200
190
180
170
(NOTE 4)
(NOTE 4)
V+ = 6.0V
V+ = 6.0V
V+ = 16.0V
V+ = 16.0V
190
180
170
160
150
V+ = 12.0V
V+ = 9.0V
V+ = 9.0V
140
130
120
V+ = 12.0V
-60 -40 -20
0
20 40 60 80 100 120 140 160
TEMPERATURE (°C)
-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 T > +85°C,
A
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
5 V, S t e p -Do w n ,
Cu rre n t -Mo d e P WM DC-DC Co n ve rt e rs
____________________________Typ ic a l Op e ra t in g Ch a ra c t e ris t ic s (c o n t in u e d )
(Circuit of Figure 3, T = +25°C, unless otherwise noted.)
A
MAX738A/MAX744A
SWITCHING WAVEFORMS,
DISCONTINUOUS CONDITION
MAX738A/MAX744A
SWITCHING WAVEFORMS,
CONTINUOUS CONDITION
12V
0V
12V
A
A
0V
200mA
0mA
200mA
B
B
C
0mA
C
2µs/div
2µs/div
A: SWITCH VOLTAGE (LX PIN), 5V/div, 0V TO +12V
B: INDUCTOR CURRENT, 200mA/div
A: SWITCH VOLTAGE (LX PIN), 5V/div, 0V TO +12V
B: INDUCTOR CURRENT, 200mA/div
C: OUTPUT VOLTAGE RIPPLE, 50mV/div, AC-COUPLED
C: OUTPUT VOLTAGE RIPPLE, 50mV/div, AC-COUPLED
C
= 390µF,
C
= 390µF,
OUT
V+ = 12V, I
OUT
V+ = 12V, I
= 150µA,
= 150µA
OUT
OUT
MAX738A/MAX744A LINE-TRANSIENT RESPONSE
MAX730A LINE-TRANSIENT RESPONSE
038/MX74A
A
B
A
B
16V
11V
6V
10.2V
0V
0V
100ms/div
100ms/div
A: V , 50mV/div, DC-COUPLED
OUT
A: V , 50mV/div, DC-COUPLED
OUT
B: V+, 5V/div, 10.2V TO 16.0V
B: V+, 5V/div, 6.0V TO 11.0V
I
= 750mA
I
= 300mA
OUT
OUT
6
_______________________________________________________________________________________
5 V, S t e p -Do w n ,
Cu rre n t -Mo d e P WM DC-DC Co n ve rt e rs
038/MX74A
____________________________Typ ic a l Op e ra t in g Ch a ra c t e ris t ic s (c o n t in u e d )
(Circuit of Figure 3, T = +25°C, unless otherwise noted.)
A
MAX730A
MAX738A/MAX744A
LOAD-TRANSIENT RESPONSE
LOAD-TRANSIENT RESPONSE
A
B
A
B
750mA
50mA
300mA
20mA
50ms/div
50ms/div
A: V , 50mV/div, DC-COUPLED
OUT
A: V , 50mV/div, DC-COUPLED
OUT
B: I , 200mA/div, 20mA TO 300mA
OUT
B: I , 500mA/div, 50mA TO 750mA
OUT
V+ = 9V
V+ = 12V
______________________________________________________________P in De s c rip t io n
PIN
NAME
FUNCTION
8-PIN
16-PIN
DIP/SO
WIDE SO
Shutdown—active low. Ground to power-down chip, tie to V+ for normal operation.
Output voltage falls to 0V when SHDN is low.
1
2
3
4
2
3
7
8
SHDN
REF
SS
Reference-Voltage Output (+1.23V) supplies up to 100µA for extended loads.
Bypass to GND with a capacitor that does not exceed 0.047µF.
Soft-Start. Capacitor between SS and GND provides soft-start and short-circuit protection.
510kΩ resistor from SS to SHDN provides current boost.
Compensation Capacitor Input externally compensates the outer feedback loop.
Connect to OUT with a 330pF capacitor.
CC
5
6
7
9
OUT
GND
LX
Output Voltage Sense Input provides regulation feedback sensing. Connect to +5V output.
Ground pins are internally connected. Connect both pins to ground.
Drain of internal P-channel power MOSFET.
10, 11
12, 13, 14
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.
8
1, 15, 16
4, 5, 6
V+
N.C.
No Connect—no internal connections to these pins.
_______________________________________________________________________________________
7
5 V, S t e p -Do w n ,
Cu rre n t -Mo d e P WM DC-DC Co n ve rt e rs
for overcurrent protection to function properly. A typical
value is 0.1µF.
_________________De t a ile d De s c rip t io n
The MAX730A/MAX738A/MAX744A switch-mode regu-
la tors us e a c urre nt-mod e p uls e -wid th-mod ula tion
(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.
Un d e rvo lt a g e Lo c k o u t
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
s up p ly volta g e fa lls b e low 5.45V (s e e the
MAX738A/MAX744A Quie s c e nt Sup p ly Curre nt vs .
Sup p ly Volta g e g ra p h in the Typ ic a l Op e ra ting
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
powe r FET off until the supply volta g e rise s a bove
approximately 4.7V (MAX730A) or 5.7V (MAX738A/
MAX744A), at which time an SS cycle begins.
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.
S h u t d o w n Mo d e
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
Ele c tric a l Cha ra c te ris tic s (s e e Sta nd b y Curre nt 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.
P ro g ra m m a b le S o ft -S t a rt
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.
038/MX74A
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 510kΩ resistor 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.
Co n t in u o u s -/Dis c o n t in u o u s -
Co n d u c t io n Mo d e s
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-
re nt de c re a se s, or the inp ut volta ge inc re a se s, 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.
The ove rc urre nt c omp a ra tor trip s whe n the loa d
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.
Ove rc u rre n t Lim it in g
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
8
_______________________________________________________________________________________
5 V, S t e p -Do w n ,
Cu rre n t -Mo d e P WM DC-DC Co n ve rt e rs
038/MX74A
Table 1. Typical Soft-Start Times
MAX730A CIRCUIT CONDITIONS
SOFT-START TIME (ms) vs. C1 (µF)
R1 (kΩ)
510
V+ (V)
I
(mA)
C4 (µF)
100
100
100
100
100
390
680
100
100
100
100
390
680
C1 = 0.01
C1 = 0.047
C1 = 0.1
C1 = 0.47
28
OUT
6
9
0
2
1
6
4
11
6
510
0
0
15
510
11
9
1
2
4
11
510
150
300
150
150
0
1
4
8
21
510
9
1
5
9
27
510
9
3
6
9
23
510
9
4
6
9
24
None
None
None
None
None
None
6
16
10
8
34
22
18
134
147
152
51
34
28
270
280
285
125
82
9
0
11
9
0
66
150
150
150
34
39
40
1263
1275
1280
9
9
MAX738A/MAX744A CIRCUIT CONDITIONS
SOFT-START TIME (ms) vs. C1 (µF)
R1 (kΩ)
510
V+ (V)
7
I
(mA)
C4 (µF)
100
C1 = 0.01
C1 = 0.047
C1 = 0.1
C1 = 0.47
OUT
0
1
1
4
2
6
3
18
8
510
12
16
12
12
7
0
0
100
510
100
1
1
2
6
510
300
750
0
100
1
3
5
3
510
100
1
5
8
21
100
54
68
1114
None
None
None
None
100
12
7
27
16
13
112
40
25
20
215
12
16
12
0
100
0
100
6
300
100
27
In t e rn a l Re fe re n c e
____________Ap p lic a t io n s In fo rm a t io n
The +1.23V bandgap reference supplies up to 100µA
at REF. Connect a 0.01µF bypass capacitor from REF
to GND.
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.
Os c illa t o r
The internal oscillator of the MAX730A typically oper-
ates at 170kHz (160kHz for the MAX738A and 185kHz
for the MAX744A). The MAX744A is g ua ra nte e d 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.
In d u c t o r S e le c t io n
The MAX730A/MAX738A/MAX744A require no inductor
d e s ig n b e c a us e the y a re te s te d in-c irc uit, a nd a re
g ua ra nte e d to d e live r the p owe r s p e c ifie d in the
Electrical Characteristics with high efficiency using a
_______________________________________________________________________________________
9
5 V, S t e p -Do w n ,
Cu rre n t -Mo d e P WM DC-DC Co n ve rt e rs
V = +6.0V TO +16.0V
IN
C2
1µF
SHDN
V+
C3*
OVERCURRENT COMPARATOR
SLOPE COMPENSATION
BIAS
GEN
RAMP
GEN
OUT
CC
Σ
R
SENSE
C5
330pF
CURRENT
SENSE AMP
ERROR AMP
F/F
R
Q
V
+5V
=
OUT
L1
S
LX
1.23V
BANDGAP
R1
510k
PWM
COMPARATOR
D1
1N5817
C4*
REF
OSC
MAX730A
MAX738A
MAX744A
C6
0.01µF
1M
±35%
SS CLAMP
SS
UNDERVOLTAGE
LOCKOUT
C1
0.1µF
V
UVLO
GND
*SEE TABLE 2 FOR COMPONENT VALUES AND SUPPLIERS
038/MX74A
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 surface-
mount inductors have nearly equivalent efficiencies to
the larger through-hole inductors.
Ca p a c itor ESR ris e s a s the te mp e ra ture fa lls , a nd
excessive ESR is the most likely cause of trouble at
te mp e ra ture s b e low 0°C. Sa nyo OS-CON s e rie s
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.
Ou t p u t Filt e r Ca p a c it o r S e le c t io n
The p rima ry c rite rion for s e le c ting the outp ut filte r
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
s ta b ility. The c a p a c itor’s ESR s hould b e le s s tha n
0.25Ω to keep the output ripple less than 50mVp-p over
the e ntire c urre nt ra ng e (us ing a 100µH ind uc tor).
Ot h e r Co m p o n e n t s
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
g ood c hoic e . The 330p F oute r-loop c omp e ns a tion
capacitor provides the widest input voltage range and
best transient characteristics. For low-current applica-
tions , the 510kΩ re s is tor ma y b e omitte d (s e e the
Maximum Output Current vs. Supply Voltage graph (R1
removed) in the Typical Operating Characteristics).
10 ______________________________________________________________________________________
5 V, S t e p -Do w n ,
Cu rre n t -Mo d e P WM DC-DC Co n ve rt e rs
038/MX74A
Table 2. Component Values and Suppliers
MAX730AC/MAX738AC/MAX744AC
Commercial Temp. Range
MAX730AE/M, MAX738AE/M, MAX744AE/M
Wide Temp. Range
Production
Method
Inductors
Capacitors
Inductors
L1 = 33µH
Capacitors
L1 = 33µH to 100µH
C3 = 68µF, 16V
C3 = 68µF, 16V
C4 = 100µF, 6.3V
C4 = 100µF, 6.3V
Sumida (708) 956-0666
CD54-101KC (MAX730AC)
CD105-101KC
Sumida (708) 956-0666
CD54-330N (MAX730AC)
CD105-330N
Surface
Mount
Matsuo (714) 969-2491
267 series
Matsuo (714) 969-2491
267 series
(MAX738AC/MAX744AC)
(MAX738AE/M, MAX744AE/M)
Sprague (603) 224-1961
595D/293D series
Sprague (603) 224-1961
595D/293D series
Coiltronics (407) 241-7876
CTX100 series
Coiltronics (407) 241-7876
CTX50 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)
C3 = 150µF, 16V
C4 = 150µF, 16V or
390µF, 6.3V
L1 = 33µH to 100µH
L1 = 33µH
Miniature
Through-
Hole
Sumida (708) 956-0666
RCH654-101K (MAX730A)
RCH895-101K
Sumida (708) 956-0666
RCH654-330M (MAX730A)
RCH895-330M
Nichicon (708) 843-7500
PL series
Low-ESR electrolytics
(MAX738A/MAX744A)
(MAX738A/MAX744A)
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
Maxim
MAXL001
100µH iron-power toroid
Maxim
Low-Cost
Through-
Hole
MAXC001
150µF, low-ESR
electrolytic
Renco (516) 586-5566
RL1284-100
United Chemicon
(708) 843-7500
P rin t e d Circ u it La yo u t s
Ou t p u t -Rip p le Filt e rin g
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.
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.
______________________________________________________________________________________ 11
5 V, S t e p -Do w n ,
Cu rre n t -Mo d e P WM DC-DC Co n ve rt e rs
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
038/MX74A
MAX738A/MAX744A +6.0V TO +16.0V
OPTIONAL LOWPASS OUTPUT FILTER
C2
1µF
L2
25µH
FILTER
OUTPUT
C3*
8
V+
OUTPUT
C7
7
1
3
2.2µF
LX
SHDN
D1
1N5817
L1*
R1
510k
MAX730A
MAX738A
MAX744A
5
4
OUTPUT
+5V
OUT
CC
C5
330pF
PART
INPUT SUPPLY RANGE (V) GUARANTEED OUTPUT CURRENT AT 5V (mA)
C4*
SS
GND
MAX730A
6.0 to 11.0
6.0 to 16.0
10.2 to 16.0
6.0 to 9.0
450
450
750
500
750
REF
MAX738A
MAX744A
C1
0.1µF
6
2
C6
0.01µF
9.0 to 16.0
NOTE: PIN NUMBERS REFER TO 8-PIN PACKAGES.
*SEE TABLE 2 FOR COMPONENT VALUES AND SUPPLIERS.
Figure 3. Standard +5V Step-Down Application Circuit
12 ______________________________________________________________________________________
5 V, S t e p -Do w n ,
Cu rre n t -Mo d e P WM DC-DC Co n ve rt e rs
038/MX74A
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
5 V, S t e p -Do w n ,
Cu rre n t -Mo d e P WM DC-DC Co n ve rt e rs
____P in Co n fig u ra t io n s (c o n t in u e d )
__Ord e rin g In fo rm a t io n (c o n t in u e d )
PART
TEMP. RANGE
0°C to +70°C
PIN-PACKAGE
8 Plastic DIP
16 Wide SO
Dice*
TOP VIEW
MAX738ACPA
MAX738ACWE
MAX738AC/D
MAX738AEPA
MAX738AEWE
MAX738AMJA
MAX744ACPA
MAX744ACWE
MAX744AC/D
MAX744AEPA
MAX744AEWE
MAX744AMJA
0°C to +70°C
SHDN
REF
SS
1
2
3
4
V+
8
7
6
5
0°C to +70°C
LX
MAX730A
-40°C to +85°C
-40°C to +85°C
-55°C to +125°C
0°C to +70°C
8 Plastic DIP
16 Wide SO
8 CERDIP
GND
OUT
CC
8 Plastic DIP
16 Wide SO
Dice*
SO
0°C to +70°C
0°C to +70°C
V+
SHDN
REF
1
2
3
4
5
6
7
8
V+
16
-40°C to +85°C
-40°C to +85°C
-55°C to +125°C
8 Plastic DIP
16 Wide SO
8 CERDIP
15 V+
14 LX
N.C.
LX
MAX738A
MAX744A
13
*Contact factory for dice specifications.
LX
N.C.
N.C.
SS
12
GND
11
10
9
GND
OUT
CC
Wide SO
__________________________________________________________Ch ip To p o g ra p h ie s
038/MX74A
MAX738A/MAX744A
MAX730A
SHDN
V+
SHDN
V+
REF
REF
LX
LX
0. 116"
(2. 946mm)
0. 131"
(3. 327mm)
SS
GND
GND
SS
CC
OUT
0. 072"
(1. 828mm)
CC
OUT
0. 116"
TRANSISTOR COUNT: 274 (MAX730A)
286 (MAX738A/MAX744A);
SUBSTRATE CONNECTED TO V+ .
(2. 946mm)
14 ______________________________________________________________________________________
5 V, S t e p -Do w n ,
Cu rre n t -Mo d e P WM DC-DC Co n ve rt e rs
038/MX74A
________________________________________________________P a c k a g e In fo rm a t io n
INCHES
MILLIMETERS
DIM
D1
MIN
MAX
0.200
–
MIN
–
MAX
5.08
–
A
–
A1 0.015
A2 0.125
A3 0.055
0.38
3.18
1.40
0.41
1.27
0.20
8.84
0.13
7.62
6.10
0.175
0.080
0.022
0.065
0.012
0.390
0.035
0.325
0.280
4.45
2.03
0.56
1.65
0.30
9.91
0.89
8.26
7.11
B
0.016
B1 0.050
C
D
0.008
0.348
E
D1 0.005
0.300
E1 0.240
E
E1
D
e
0.100 BSC
0.300 BSC
2.54 BSC
7.62 BSC
A3
e
A
B
A2
A1
A
L
e
–
0.115
0˚
0.400
0.150
15˚
–
10.16
3.81
L
2.92
0˚
α
15˚
21-324A
α
8-PIN PLASTIC
DUAL-IN-LINE
PACKAGE
C
e
B1
e
e
A
B
B
INCHES
MILLIMETERS
DIM
MIN
0.053
MAX
0.069
0.010
0.019
0.010
0.197
0.157
MIN
1.35
0.10
0.35
0.19
4.80
3.80
MAX
1.75
0.25
0.49
0.25
5.00
4.00
A
A1 0.004
B
C
D
E
e
0.014
0.007
0.189
0.150
E
H
0.050 BSC
1.27 BSC
H
h
0.228
0.010
0.016
0˚
0.244
0.020
0.050
8˚
5.80
0.25
0.40
0˚
6.20
0.50
1.27
L
α
8˚
21-325A
h x 45˚
D
α
A
0.127mm
0.004in.
8-PIN PLASTIC
SMALL-OUTLINE
PACKAGE
e
A1
C
L
B
______________________________________________________________________________________ 15
5 V, S t e p -Do w n ,
Cu rre n t -Mo d e P WM DC-DC Co n ve rt e rs
___________________________________________P a c k a g e In fo rm a t io n (c o n t in u e d )
INCHES
MIN
MILLIMETERS
DIM
MAX
0.200
0.023
0.065
0.045
0.015
0.405
0.310
0.320
MIN
–
MAX
5.08
0.58
1.65
1.14
0.38
10.29
7.87
8.13
A
B
–
S1
S
0.014
0.36
0.97
0.58
0.20
–
B1 0.038
B2 0.023
C
D
E
0.008
–
0.220
5.59
7.37
E1 0.290
E1
E
e
L
0.100 BSC
2.54 BSC
D
0.125
0.150
0.015
–
0.200
–
3.18
3.81
0.38
–
5.08
–
L1
Q
S
B2
A
0.060
0.055
–
1.52
1.40
–
S1 0.005
0.13
0˚
α
0˚
15˚
15˚
21-326D
α
Q
L
L1
B1
C
8-PIN CERAMIC
DUAL-IN-LINE
PACKAGE
e
B
INCHES
MILLIMETERS
DIM
038/MX74A
MIN
0.093
MAX
0.104
0.012
0.019
0.013
0.413
0.299
MIN
2.35
0.10
0.35
0.23
10.10
7.40
MAX
2.65
0.30
0.49
0.32
10.50
7.60
A
A1 0.004
B
C
D
E
e
0.014
0.009
0.398
0.291
E
H
0.050 BSC
1.27 BSC
H
h
0.394
0.010
0.016
0˚
0.419
0.030
0.050
8˚
10.00
0.25
0.40
0˚
10.65
0.75
1.27
L
α
8˚
21-589B
h x 45˚
D
α
A
0.127mm
0.004in.
16-PIN PLASTIC
SMALL-OUTLINE
(WIDE)
e
A1
C
B
L
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 __________________Ma x im In t e g ra t e d P ro d u c t s , 1 2 0 S a n Ga b rie l Drive , S u n n yva le , CA 9 4 0 8 6 (4 0 8 ) 7 3 7 -7 6 0 0
© 1996 Maxim Integrated Products
Printed USA
is a registered trademark of Maxim Integrated Products.
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