MAX1733EUK [MAXIM]
Low-Voltage, Step-Down DC-DC Converters in SOT23; 低电压，降压型DC -DC转换器，SOT23封装
| 型号： | MAX1733EUK |
| 厂家： | 
MAXIM INTEGRATED PRODUCTS |
| 描述： | Low-Voltage, Step-Down DC-DC Converters in SOT23 |
| 文件： | 总8页 (文件大小：266K) |
| 中文： | 中文翻译 | 下载： | 下载PDF数据表文档文件 |
19-1586; Rev 0; 7/00
Low-Voltage, Step-Down DC-DC Converters
in SOT23
General Description
Features
The MAX1733/MAX1734 step-down DC-DC converters
deliver over 250mA to outputs as low as 1.25V. These
converters use a unique proprietary current-limited con-
trol scheme that achieves over 90% efficiency. These
devices maintain extremely low quiescent supply cur-
rent (40µA), and their high 1.2MHz (max) operating fre-
quency permits small, low-cost external components.
This combination of features makes the MAX1733/
MAX1734 excellent high-efficiency alternatives to linear
regulators in space-constrained applications.
ꢀ 250mA Guaranteed Output Current
ꢀ Synchronous Rectifier for Over 90% Efficiency
ꢀ Tiny 5-Pin SOT23 Package
ꢀ 40µA Quiescent Supply Current
ꢀ 0.01µA Logic-Controlled Shutdown
ꢀ Up to 1.2MHz Switching Frequency
ꢀ Fixed 1.8V or 1.5V Outputs (MAX1734)
ꢀ Adjustable Output Voltage (MAX1733)
Internal synchronous rectification greatly improves effi-
ciency and eliminates the external Schottky diode
required in conventional step-down converters. Both
devices also include internal digital soft-start to limit
input current upon startup and reduce input capacitor
requirements.
ꢀ
1.5% ꢀnitial Accuracy
ꢀ 2.7V to 5.5V ꢀnput Range
ꢀ Soft-Start Limits Startup Current
The MAX1733 provides an adjustable output voltage
(1.25V to 2.0V). The MAX1734 provides factory-preset
output voltages (see Selector Guide). Both are avail-
able in space-saving 5-pin SOT23 packages.
Ordering Information
PART
TEMP. RANGE
-40°C to +85°C
-40°C to +85°C
PꢀN-PACKAGE
5 SOT23-5
MAX1733EUK-T
MAX1734EUK_ _-T
5 SOT23-5
Note: The MAX1734 offers two output voltages. See the Selector
Guide, then insert the proper designator into the blanks above to
complete the part number.
Applications
Cellular, PCS, and Cordless Telephones
PDAs, Palmtops, and Handy-Terminals
Battery-Powered Equipment
Selector Guide
PART
V
(V)
TOP MARK
ADKY
OUT
MAX1733EUK
MAX1734EUK18
MAX1734EUK15
Adjustable
1.8
ADKW
1.5
ADKX
Typical Operating Circuit
Pin Configuration
TOP VIEW
INPUT
+2.7V TO +5.5V
V
AT
OUT
250mA
10µH
IN
LX
IN
1
2
3
5
4
LX
2.2µF
22µF
MAX1734
MAX1733
MAX1734
GND
SHDN
OUT
SHDN
OUT (FB)
GND
SOT23-5
( ) ARE FOR MAX1733 ONLY.
________________________________________________________________ Maxim Integrated Products
1
For free samples and the latest literature, visit www.maxim-ic.com or phone 1-800-998-8800.
For small orders, phone 1-800-835-8769.
Low-Voltage, Step-Down DC-DC Converters
in SOT23
ABSOLUTE MAXꢀMUM RATꢀNGS
IN, SHDN to GND.....................................................-0.3V to +6V
OUT, FB, LX to GND....................................-0.3V to (V + 0.3V)
OUT Short Circuit to GND ..........................................Continuous
Operating Temperature Range ...........................-40°C to +85°C
Junction Temperature......................................................+150°C
Storage Temperature Range.............................-65°C to +150°C
Lead Temperature (soldering, 10s) .................................+300°C
IN
Continuous Power Dissipation (T = +70°C)
A
5-Pin SOT23 (derate 7.1mW/°C above +70°C)............571mW
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.
ELECTRꢀCAL CHARACTERꢀSTꢀCS
(V = +2.7V to +5.5V, SHDN = IN, T = 0°C to +85°C. Typical values are at T = +25°C, unless otherwise noted.)
IN
A
A
PARAMETER
SYMBOL
CONDITIONS
MIN
TYP
MAX
5.5
UNITS
Input Voltage Range
Startup Voltage
V
2.7
V
V
IN
V
2.0
START
V
V
rising
falling
1.85
1.65
200
1.95
IN
IN
UVLO Threshold
V
V
UVLO
1.55
UVLO Hysteresis
mV
µA
No switching, no load (FB/OUT above trip
point)
Quiescent Supply Current
I
40
70
IN
Shutdown Supply Current
I
SHDN = GND
0.01
4
µA
SHDN
Output Voltage Range (MAX1733)
V
1.25
-1.5
-3
2.0
+1.5
+3
V
OUT
I
I
I
= 0, T = +25°C
OUT
OUT
OUT
A
Output Voltage Accuracy
(MAX1734)
%
= 0 to 250mA
= 0 to 250mA
= 2.7V to 5.5V
Load Regulation
0
0
%/mA
%/V
µA
Line Regulation
V
V
IN
OUT Sense Current (MAX1734)
= V , V = V = 5V
REG IN SHDN
4
8
OUT
T
= +25°C, V = 3.6V
1.231
1.220
1.250
1.269
1.280
0.2
A
IN
FB Feedback Threshold
(MAX1733)
V
V
FB
V
V
= 3.6V
= 1.5V
IN
FB Leakage Current (MAX1733)
SHDN Input High Voltage
SHDN Input Low Voltage
SHDN Leakage Current
High-Side Current Limit
Low-Side Current Limit
I
FB
0.001
µA
V
FB
V
2.7V < V < 5.5V
1.6
IH
IN
V
IL
SHDN
2.7V < V < 5.5V
IN
0.4
1
V
I
SHDN = GND or IN
0.001
425
325
0.7
0.5
1.0
0.8
40
µA
mA
mA
I
300
200
535
430
1.4
1.1
2
LIMP
I
LIMN
I
LX
I
LX
I
LX
I
LX
= -50mA, V = 3.0V
IN
High-Side On-Resistance
Rectifier On-Resistance
R
Ω
Ω
ONP
ONN
= -50mA, V = 5.5V
IN
= -50mA, V = 3.0V
IN
R
= -50mA, V = 5.5V
1.6
IN
Rectifier Off-Current Threshold
LX Leakage Current
I
mA
µA
µA
µs
LXOFF
I
V
= 5.5V, V = 0 to V
IN
0.1
0.1
0.4
0.4
5
LXLEAK
IN
LX
LX Reverse Leakage Current
Minimum On-Time
I
IN unconnected, V = 5.5V, SHDN = GND
5
LXLK,R
LX
t
t
V
V
= 3.6V
= 3.6V
0.28
0.28
0.5
0.5
ON(MIN)
IN
IN
Minimum Off-Time
µs
OFF(MIN)
2
_______________________________________________________________________________________
Low-Voltage, Step-Down DC-DC Converters
in SOT23
ELECTRICAL CHARACTERISTICS
(V = +2.7V to +5.5V, SHDN = IN, T = -40°C to +85°C, unless otherwise noted.) (Note 1)
IN
A
PARAMETER
SYMBOL
CONDITIONS
MIN
MAX
5.5
UNITS
Input Voltage Range
Startup Voltage
V
2.7
V
V
IN
V
2.0
START
V
V
rising, 200mV typical hysteresis
falling
1.95
IN
IN
UVLO Threshold
V
V
UVLO
1.55
Quiescent Supply Current
Shutdown Supply Current
Output Voltage Range (MAX1733)
I
No switching (FB/OUT above trip point)
70
4
µA
µA
V
IN
I
SHDN = GND
SHDN
V
1.25
-3
2.0
OUT
Output Voltage Accuracy
(MAX1734)
I
= 0 to 250mA
+3
8
%
µA
V
OUT
OUT Sense Current (MAX1734)
I
V
V
V
= V
, V = V
REG IN
= 5V
SHDN
OUT
OUT
FB Feedback Threshold
(MAX1733)
V
= 3.6V
1.210
1.6
1.280
0.2
FB
IN
FB Leakage Current (MAX1733)
SHDN Input High Voltage
SHDN Input Low Voltage
SHDN Leakage Current
High-Side Current Limit
Low-Side Current Limit
I
= 1.5V
µA
V
FB
FB
V
2.7V < V < 5.5V
IN
IH
V
IL
SHDN
2.7V < V < 5.5V
IN
0.4
1
V
I
SHDN = GND or IN
µA
mA
mA
I
300
200
565
430
1.4
1.1
2
LIMP
I
LIMN
I
LX
I
LX
I
LX
I
LX
= -50mA, V = 3.0V
IN
High-Side On-Resistance
Rectifier On-Resistance
R
Ω
Ω
ONP
ONN
= -50mA, V = 5.5V
IN
= -50mA, V = 3.0V
IN
R
= -50mA, V = 5.5V
1.6
5
IN
LX Leakage Current
LX Reverse Leakage Current
Minimum On-Time
I
V
= 5.5V, V = 0 to V
IN
µA
µA
µs
µs
LXLEAK
IN
LX
I
IN unconnected, V = 5.5V, SHDN = GND
5
LXLK,R
LX
t
t
0.25
0.25
0.55
0.55
ON(MIN)
Minimum Off-Time
OFF(MIN)
Note 1: All devices are 100% production tested at T = +25°C. Limits over the operating temperature range are guaranteed by design.
A
_______________________________________________________________________________________
3
Low-Voltage, Step-Down DC-DC Converters
in SOT23
Typical Operating Characteristics
(C = 2.2µF ceramic, C
= 22µF tantalum, L = 10µH, unless otherwise noted.)
IN
OUT
EFFICIENCY vs.
NO-LOAD SUPPLY CURRENT
vs. SUPPLY VOLTAGE
LOAD CURRENT (V
= 1.5V)
OUT
100
90
100
90
62
60
58
56
54
52
50
48
46
V
IN
= 2.7V
V
IN
= 2.7V
V
= 1.8V, T = +85°C
OUT A
V
= 1.8V, T = +25°C
A
80
70
60
OUT
80
70
60
V
= 5.0V
IN
V
= 5.0V
IN
V
= 3.6V
IN
V
= 3.6V
IN
50
40
30
50
40
30
V
OUT
= 1.5V, T = +25°C
A
V
= 1.5V, T = -40°C
A
OUT
0.1
1
10
LOAD CURRENT (mA)
100
1000
2.5
3.0
3.5
4.0
4.5
5.0
5.5
0.1
1
10
100
1000
SUPPLY VOLTAGE (V)
LOAD CURRENT (mA)
OUTPUT ACCURACY vs.
LOAD CURRENT (V = 1.5V)
SWITCHING FREQUENCY
vs. SUPPLY VOLTAGE
OUTPUT ACCURACY vs.
LOAD CURRENT (V = 1.8V)
OUT
OUT
3.0
2.0
1.0
0
3.0
2.0
1.0
0
1.50
1.25
1.00
0.75
0.50
I
= 50mA TO 250mA
LOAD
V
IN
= 3.6V, T = +85°C
A
V
IN
= 3.6V, T = +85°C
A
V
IN
= 5.0V, T = +25°C
A
V
IN
= 2.7V, T = +25°C
A
-1.0
-2.0
-3.0
-1.0
-2.0
-3.0
V
= 1.8V
3.3
OUT
V
OUT
= 1.5V
V
= 2.7V, T = +25°C
A
IN
V
= 5.0V, T = +25°C
A
IN
V
IN
= 3.6V, T = -40°C
A
V
IN
= 3.6V, T = -40°C
A
0.1
1
10
100
1000
2.7
3.0
3.6
3.9
4.2
0.1
1
10
100
1000
LOAD CURRENT (mA)
SUPPLY VOLTAGE (V)
LOAD CURRENT (mA)
LIGHT-LOAD SWITCHING WAVEFORMS
HEAVY-LOAD SWITCHING WAVEFORMS
MAX1733/4-07
MAX1733/4-08
V
IN
= 3.6V, V
= 1.8V, I
= 20mA
OUT
LOAD
V
IN
= 3.6V, V
= 1.8V, I
= 200mA
OUT
LOAD
V
OUT
AC-COUPLED
V
OUT
AC-COUPLED
20mV/div
20mV/div
V
LX
2V/div
V
LX
2V/div
400ns/div
400ns/div
4
_______________________________________________________________________________________
Low-Voltage, Step-Down DC-DC Converters
in SOT23
Typical Operating Characteristics (continued)
(C = 2.2µF ceramic, C
= 22µF tantalum, L = 10µH, unless otherwise noted.)
IN
OUT
LOAD-TRANSIENT RESPONSE
SOFT-START AND SHUTDOWN RESPONSE
MAX1733/4-12
MAX1733/4-09
V
IN
= 3.6V, V
= 1.8V, I
= 20mA TO 200mA
V
IN
= 3.6V, V
= 1.8V, R
= 7Ω
OUT
LOAD
OUT
LOAD
V
OUT
1V/div
V
OUT
AC-COUPLED
50mV/div
I
IN
100mA/div
I
LOAD
100mA/div
V
SHDN
5V/div
4µs/div
200µs/div
HEAVY-LOAD LINE-TRANSIENT RESPONSE
LIGHT-LOAD LINE-TRANSIENT RESPONSE
MAX1733/4-11
MAX1733/4-10
V
IN
= 3.4V TO 3.8V, V
= 1.8V, I
= 200mA
LOAD
V
IN
= 3.4V TO 3.8V, V
= 1.8V, I
= 20mA
OUT
OUT
LOAD
V
V
OUT
AC-COUPLED
OUT
AC-COUPLED
50mV/div
50mV/div
V
IN
V
IN
AC-COUPLED
AC-COUPLED
200mV/div
200mV/div
4µs/div
4µs/div
Pin Description
PIN
1
NAME
IN
FUNCTION
Supply Voltage Input. Input range from +2.7V to +5.5V. Bypass with a 2.2µF ceramic capacitor to
GND.
2
GND
SHDN
Ground
Active-Low Shutdown Input. Connect SHDN to IN for normal operation. In shutdown, LX becomes
high impedance and quiescent current drops to 0.01µA.
3
MAX1733 Voltage Feedback Input. FB regulates to 1.25V nominal. Connect FB to an external
voltage-divider between the output voltage and GND.
FB
4
5
OUT
LX
MAX1734 Voltage Sense Input. OUT is connected to an internal voltage-divider.
Inductor Connection
_______________________________________________________________________________________
5
Low-Voltage, Step-Down DC-DC Converters
in SOT23
L1
10µH
INPUT
IN
V
OUT
+2.7V TO +5.5V
IN
LX
FB
C1
2.2µF
C2
22µF
MAX1733
MAX1733
MAX1734
CURRENT
LIMIT
R1
R2
SHDN
GND
DIGITAL
SOFT-START
P
CONTROL
LOGIC
LX
N
Figure 1. MAX1733 Typical Application Circuit
SHUTDOWN
CONTROL
SHDN
OUT (FB)
Detailed Description
The MAX1733/MAX1734 step-down DC-DC converters
deliver over 250mA to outputs as low as 1.25V. They
use a unique proprietary current-limited control scheme
that maintains extremely low quiescent supply current
(40µA), and their high 1.2MHz (max) operating frequen-
cy permits small, low-cost external components. Figure
2 is a simplified functional diagram.
V
REF
GND
( ) ARE FOR MAX1733 ONLY.
Figure 2. Simplified Functional Diagram
Control Scheme
The MAX1733/MAX1734 use a proprietary, current-lim-
ited control scheme to ensure high-efficiency, fast tran-
sient response, and physically small external
components. This control scheme is simple: when the
output voltage is out of regulation, the error comparator
begins a switching cycle by turning on the high-side
switch. This switch remains on until the minimum on-
time of 400ns expires and the output voltage regulates
or the current-limit threshold is exceeded. Once off, the
high-side switch remains off until the minimum off-time
of 400ns expires and the output voltage falls out of reg-
ulation. During this period, the low-side synchronous
rectifier turns on and remains on until either the high-
side switch turns on again or the inductor current
approaches zero. The internal synchronous rectifier
eliminates the need for an external Schottky diode.
nearly constant frequency operation with high efficien-
cy and low output voltage ripple.
Shutdown Mode
Connecting SHDN to GND places the MAX1733/
MAX1734 in shutdown mode and reduces supply cur-
rent to 0.01µA. In shutdown, the control circuitry, inter-
nal switching MOSFET, and synchronous rectifier turn
off and LX goes high impedance. Connect SHDN to IN
for normal operation.
Soft-Start
The MAX1733/MAX1734 have internal soft-start circuitry
that limits current draw at startup, reducing transients on
the input source. Soft-start is particularly useful for higher
impedance input sources, such as Li+ and alkaline cells.
Soft-start is implemented by starting with the current limit
at 25% of its full current value and gradually increasing it
in 25% steps until the full current limit is reached. See
Soft-Start and Shutdown Response in the Typical
Operating Characteristics section.
This control scheme allows the MAX1733/MAX1734 to
provide excellent performance throughout the entire
load-current range. When delivering light loads, the
high-side switch turns off after the minimum on-time to
reduce peak inductor current, resulting in increased
efficiency and reduced output voltage ripple. When
delivering medium and higher output currents, the
MAX1733/MAX1734 extend either the on-time or the off-
time, as necessary to maintain regulation, resulting in
Design Information
Setting the Output Voltage (MAX1733)
Select an output voltage for the MAX1733 by connect-
ing FB to a resistive divider between the output and
6
_______________________________________________________________________________________
Low-Voltage, Step-Down DC-DC Converters
in SOT23
Table 1. Suggested Inductors
Table 3. Component Suppliers
COMPANY
PHONE
FAX
INDUCTOR VALUE
(µH)
PART
NUMBER
MANUFACTURER
AVX
843-946-0238
847-639-6400
408-986-0424
814-237-1431
847-956-0666
81-3-3607-5111
408-573-4150
843-626-3123
847-639-1469
408-986-1442
814-238-0490
847-956-0702
81-3-3607-5144
408-573-4159
Coilcraft
Kemet
CR43-100
10
10
Sumida
Coilcraft
CDRH4D18-100
DT1608C-103
Murata
USA
Sumida
Japan
Table 2. Suggested Capacitors
Taiyo Yuden
CAPACITOR
MANUFACTURER
TYPE
PART
NUMBER
1/2
Tantalum
(22µF)
I
V
V
− OUT
Taiyo Yuden
AVX
LMK212BJ225MG
TAJA226M006R
OUT OUT
(
IN
)
I
=
RMS
V
Ceramic
(2.2µF)
IN
Tables 2 and 3 list some suggested capacitors and
suppliers.
Using Ceramic C
with MAX1733
OUT
GND (Figure 1). Choose R2 to be less than 50kΩ:
The circuit of Figure 3 is designed to allow the use of
ceramic output capacitors with the MAX1733.
Feedback is derived from the LX pin instead of the out-
put to remove the effects of phase lag in the feedback
loop. Compared to the standard applications circuit,
there are three benefits: 1) availability of ceramic vs.
tantalum; 2) size of 2.2µF 0805 vs. 22µF A-case; 3) out-
put ripple less than 10mVp-p vs. greater than 30mVp-p.
Increase the output capacitance to 4.7µF to further
reduce the output ripple. Note that this circuit exhibits
load regulation equal to the series resistance of the
inductor multiplied by the load current. This small
amount of load regulation is helpful in reducing over-
shoot of the output voltage during load transients.
V
OUT
R1 = R2 ×
−1
V
REF
where V
= 1.25V.
REF
Inductor Selection
The MAX1733/MAX1734 are optimized to use a 10µH
inductor over the entire operating range. A 300mA
rated inductor is enough to prevent saturation for out-
put currents up to 250mA. Saturation occurs when the
inductor’s magnetic flux density reaches the maximum
level the core can support and inductance falls.
Choose a low DC-resistance inductor to improve effi-
ciency. Tables 1 and 3 list some suggested inductors
and suppliers.
OUTPUT
1.8V at 250mA
10µH
IN
LX
FB
Capacitor Selection
The MAX1733/MAX1734 require output voltage ripple
(approximately 30mVp-p) for stable switching behavior.
Use a 10µF to 47µF tantalum output capacitor with
about 200mΩ to 300mΩ ESR to provide stable switch-
ing while minimizing output ripple. Choose input and
output capacitors to filter inductor currents for accept-
able voltage ripple. The input capacitor reduces peak
currents and noise at the voltage source. Input capaci-
tors must meet the input ripple requirements and volt-
age rating. Use the following equation to calculate the
maximum RMS input current:
2.2µF
X7R
Li+
2.2µF
X7R
MAX1733
30k
2.7V TO 4.2V
GND
1000pF
ON OFF
SHDN
68k
Figure 3. Using a Ceramic Output Capacitor with the MAX1733
_______________________________________________________________________________________
7
Low-Voltage, Step-Down DC-DC Converters
in SOT23
age-feedback network; also keep them separate, using
grounded copper. The MAX1733/MAX1734 evaluation
kit data sheet includes a proper PC board layout and
routing scheme.
Layout Considerations
High switching frequencies make PC board layout a
very important part of design. Good design minimizes
excessive EMI on the feedback paths and voltage gra-
dients in the ground plane, both of which can result in
instability or regulation errors. Connect the inductor,
input filter capacitor, and output filter capacitor as
close to the device as possible, and keep their traces
short, direct, and wide. Connect their ground pins at a
single common node in a star ground configuration.
The external voltage-feedback network should be very
close to the FB pin, within 0.2 inches (5mm). Keep
noisy traces, such as the LX trace, away from the volt-
Chip Information
TRANSISTOR COUNT: 1190
PROCESS: BiCMOS
Package Information
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.
8 _____________________Maxim Integrated Products, 120 San Gabriel Drive, Sunnyvale, CA 94086 408-737-7600
© 2000 Maxim Integrated Products
Printed USA
is a registered trademark of Maxim Integrated Products.
相关型号：
MAX1733EUK+
Switching Regulator, Voltage-mode, 0.565A, 1200kHz Switching Freq-Max, BICMOS, PDSO5, LEAD FREE, SOT-23, 5 PIN
MAXIM
MAX1733EUK-TG05
Switching Regulator, 0.565A, 1200kHz Switching Freq-Max, BICMOS, PDSO5, SOT-23, 5 PIN
MAXIM
MAX1734EUK18+
Switching Regulator, 0.565A, 1200kHz Switching Freq-Max, BICMOS, PDSO5, LEAD FREE, SOT-23, 5 PIN
MAXIM
©2020 ICPDF网 联系我们和版权申明