Maxim MAX1734EUK -T Low-voltage, step-down dc-dc converters in sot23 Datasheet

19-1586; Rev 0; 7/00
Low-Voltage, Step-Down DC-DC Converters
in SOT23
Features
♦ 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)
♦ ±1.5% Initial Accuracy
♦ 2.7V to 5.5V Input Range
♦ Soft-Start Limits Startup Current
Ordering Information
PART
Applications
Cellular, PCS, and Cordless Telephones
TEMP. RANGE
MAX1733EUK-T
-40°C to +85°C
5 SOT23-5
MAX1734EUK_ _-T
-40°C to +85°C
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.
Selector Guide
PDAs, Palmtops, and Handy-Terminals
Battery-Powered Equipment
PART
VOUT (V)
MAX1733EUK
10µH
IN
VOUT AT
250mA
Adjustable
ADKY
1.8
ADKW
MAX1734EUK15
1.5
ADKX
Pin Configuration
TOP VIEW
LX
IN
2.2µF
TOP MARK
MAX1734EUK18
Typical Operating Circuit
INPUT
+2.7V TO +5.5V
PIN-PACKAGE
SHDN
GND
1
5
LX
4
OUT (FB)
22µF
MAX1734
OUT
GND 2
MAX1733
MAX1734
SHDN 3
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.
MAX1733/MAX1734
General Description
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 control scheme that achieves over 90% efficiency. These
devices maintain extremely low quiescent supply current (40µA), and their high 1.2MHz (max) operating frequency 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.
Internal synchronous rectification greatly improves efficiency 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.
The MAX1733 provides an adjustable output voltage
(1.25V to 2.0V). The MAX1734 provides factory-preset
output voltages (see Selector Guide). Both are available in space-saving 5-pin SOT23 packages.
MAX1733/MAX1734
Low-Voltage, Step-Down DC-DC Converters
in SOT23
ABSOLUTE MAXIMUM RATINGS
IN, SHDN to GND .....................................................-0.3V to +6V
OUT, FB, LX to GND ....................................-0.3V to (VIN + 0.3V)
OUT Short Circuit to GND ..........................................Continuous
Continuous Power Dissipation (TA = +70°C)
5-Pin SOT23 (derate 7.1mW/°C above +70°C)............571mW
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
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
(VIN = +2.7V to +5.5V, SHDN = IN, TA = 0°C to +85°C. Typical values are at TA = +25°C, unless otherwise noted.)
PARAMETER
Input Voltage Range
SYMBOL
CONDITIONS
VIN
Startup Voltage
VSTART
UVLO Threshold
VUVLO
MIN
TYP
2.7
VIN rising
VIN falling
1.85
1.55
UVLO Hysteresis
MAX
V
2.0
V
1.95
1.65
200
Quiescent Supply Current
IIN
Shutdown Supply Current
ISHDN
Output Voltage Range (MAX1733)
VOUT
No switching, no load (FB/OUT above trip
point)
µA
0.01
4
µA
1.25
2.0
V
-1.5
+1.5
-3
+3
IOUT = 0 to 250mA
Load Regulation
IOUT = 0 to 250mA
0
Line Regulation
VIN = 2.7V to 5.5V
0
OUT Sense Current (MAX1734)
VOUT = VREG, VIN = V SHDN= 5V
4
TA = +25°C, VIN = 3.6V
1.231
VIN = 3.6V
1.220
VFB
FB Leakage Current (MAX1733)
IFB
VFB = 1.5V
SHDN Input High Voltage
VIH
2.7V < VIN < 5.5V
SHDN Input Low Voltage
VIL
2.7V < VIN < 5.5V
SHDN Leakage Current
ISHDN
High-Side Current Limit
ILIMP
Low-Side Current Limit
ILIMN
mV
70
Output Voltage Accuracy
(MAX1734)
FB Feedback Threshold
(MAX1733)
V
40
SHDN = GND
IOUT = 0, TA = +25°C
UNITS
5.5
1.250
%/mA
%/V
8
1.269
1.280
0.001
%
0.2
1.6
µA
V
µA
V
0.4
V
0.001
1
µA
300
425
535
mA
200
mA
SHDN = GND or IN
325
430
ILX = -50mA, VIN = 3.0V
0.7
1.4
ILX = -50mA, VIN = 5.5V
0.5
1.1
ILX = -50mA, VIN = 3.0V
1.0
2
ILX = -50mA, VIN = 5.5V
0.8
1.6
Ω
High-Side On-Resistance
RONP
Rectifier On-Resistance
RONN
Rectifier Off-Current Threshold
ILXOFF
LX Leakage Current
ILXLEAK
VIN = 5.5V, VLX = 0 to VIN
0.1
5
µA
LX Reverse Leakage Current
ILXLK,R
IN unconnected, VLX = 5.5V, SHDN = GND
0.1
5
µA
40
Ω
mA
Minimum On-Time
tON(MIN)
VIN = 3.6V
0.28
0.4
0.5
µs
Minimum Off-Time
tOFF(MIN)
VIN = 3.6V
0.28
0.4
0.5
µs
2
_______________________________________________________________________________________
Low-Voltage, Step-Down DC-DC Converters
in SOT23
(VIN = +2.7V to +5.5V, SHDN = IN, TA = -40°C to +85°C, unless otherwise noted.) (Note 1)
PARAMETER
Input Voltage Range
SYMBOL
CONDITIONS
VIN
Startup Voltage
VSTART
UVLO Threshold
VUVLO
Quiescent Supply Current
IIN
Shutdown Supply Current
ISHDN
Output Voltage Range (MAX1733)
VOUT
Output Voltage Accuracy
(MAX1734)
MIN
2.7
VIN rising, 200mV typical hysteresis
VIN falling
MAX
UNITS
5.5
V
2.0
V
1.95
1.55
V
No switching (FB/OUT above trip point)
70
µA
SHDN = GND
4
µA
1.25
2.0
V
-3
+3
%
8
µA
1.280
V
0.2
µA
IOUT = 0 to 250mA
OUT Sense Current (MAX1734)
IOUT
VOUT = VREG, VIN = V SHDN = 5V
FB Feedback Threshold
(MAX1733)
VFB
VIN = 3.6V
FB Leakage Current (MAX1733)
IFB
VFB = 1.5V
SHDN Input High Voltage
VIH
2.7V < VIN < 5.5V
SHDN Input Low Voltage
VIL
2.7V < VIN < 5.5V
SHDN Leakage Current
ISHDN
1
µA
High-Side Current Limit
ILIMP
300
565
mA
Low-Side Current Limit
ILIMN
200
430
mA
High-Side On-Resistance
RONP
Rectifier On-Resistance
RONN
1.210
1.6
V
0.4
SHDN = GND or IN
ILX = -50mA, VIN = 3.0V
1.4
ILX = -50mA, VIN = 5.5V
1.1
ILX = -50mA, VIN = 3.0V
2
ILX = -50mA, VIN = 5.5V
1.6
V
Ω
Ω
LX Leakage Current
ILXLEAK
VIN = 5.5V, VLX = 0 to VIN
5
µA
LX Reverse Leakage Current
ILXLK,R
IN unconnected, VLX = 5.5V, SHDN = GND
5
µA
Minimum On-Time
tON(MIN)
0.25
0.55
µs
Minimum Off-Time
tOFF(MIN)
0.25
0.55
µs
Note 1: All devices are 100% production tested at TA = +25°C. Limits over the operating temperature range are guaranteed by design.
_______________________________________________________________________________________
3
MAX1733/MAX1734
ELECTRICAL CHARACTERISTICS
Typical Operating Characteristics
(CIN = 2.2µF ceramic, COUT = 22µF tantalum, L = 10µH, unless otherwise noted.)
EFFICIENCY vs.
LOAD CURRENT (VOUT = 1.5V)
90
90
EFFICIENCY (%)
VIN = 5.0V
70
VIN = 3.6V
60
VIN = 5.0V
70
VIN = 3.6V
60
58
54
52
40
40
48
30
30
46
0.1
1000
-1.0
VIN = 5.0V, TA = +25°C
1.0
0
-1.0
VIN = 2.7V, TA = +25°C
-2.0
VIN = 5.0V, TA = +25°C
-3.0
10
100
3.5
4.0
4.5
5.0
5.5
1.50
ILOAD = 50mA TO 250mA
1.25
1.00
VOUT = 1.8V
VOUT = 1.5V
0.75
VIN = 3.6V, TA = -40°C
VIN = 3.6V, TA = -40°C
-3.0
1
3.0
SWITCHING FREQUENCY
vs. SUPPLY VOLTAGE
SWITCHING FREQUENCY (MHz)
VIN = 2.7V, TA = +25°C
0.1
VOUT = 1.5V, TA = -40°C
SUPPLY VOLTAGE (V)
VIN = 3.6V, TA = +85°C
2.0
OUTPUT ACCURACY (%)
VIN = 3.6V, TA = +85°C
0
-2.0
VOUT = 1.5V, TA = +25°C
2.5
1000
3.0
MAX1733/4-04
3.0
1.0
10
100
LOAD CURRENT (mA)
50
OUTPUT ACCURACY vs.
LOAD CURRENT (VOUT = 1.5V)
OUTPUT ACCURACY vs.
LOAD CURRENT (VOUT = 1.8V)
2.0
1
MAX1733/4-05
10
100
LOAD CURRENT (mA)
VOUT = 1.8V, TA = +25°C
56
50
1
VOUT = 1.8V, TA = +85°C
60
50
0.1
1000
0.50
0.1
1
10
100
1000
2.7
3.0
LOAD CURRENT (mA)
LOAD CURRENT (mA)
LIGHT-LOAD SWITCHING WAVEFORMS
3.6
MAX1733/4-08
VIN = 3.6V, VOUT = 1.8V, ILOAD = 20mA
400ns/div
3.3
SUPPLY VOLTAGE (V)
HEAVY-LOAD SWITCHING WAVEFORMS
MAX1733/4-07
4
62
SUPPLY CURRENT (µA)
80
80
EFFICIENCY (%)
VIN = 2.7V
MAX1733/4-03
VIN = 2.7V
MAX1733/4-02
100
MAX1733/4-01
100
NO-LOAD SUPPLY CURRENT
vs. SUPPLY VOLTAGE
MAX1733/4-06
EFFICIENCY vs.
LOAD CURRENT (VOUT = 1.8V)
OUTPUT ACCURACY (%)
MAX1733/MAX1734
Low-Voltage, Step-Down DC-DC Converters
in SOT23
VIN = 3.6V, VOUT = 1.8V, ILOAD = 200mA
VOUT
AC-COUPLED
20mV/div
VOUT
AC-COUPLED
20mV/div
VLX
2V/div
VLX
2V/div
400ns/div
_______________________________________________________________________________________
3.9
4.2
Low-Voltage, Step-Down DC-DC Converters
in SOT23
LOAD-TRANSIENT RESPONSE
SOFT-START AND SHUTDOWN RESPONSE
MAX1733/4-12
MAX1733/4-09
VIN = 3.6V, VOUT = 1.8V, ILOAD = 20mA TO 200mA
VIN = 3.6V, VOUT = 1.8V, RLOAD = 7Ω
VOUT
1V/div
VOUT
AC-COUPLED
50mV/div
IIN
100mA/div
ILOAD
100mA/div
VSHDN
5V/div
4µs/div
200µs/div
HEAVY-LOAD LINE-TRANSIENT RESPONSE
LIGHT-LOAD LINE-TRANSIENT RESPONSE
MAX1733/4-11
MAX1733/4-10
VIN = 3.4V TO 3.8V, VOUT = 1.8V, ILOAD = 200mA
VIN = 3.4V TO 3.8V, VOUT = 1.8V, ILOAD = 20mA
VOUT
AC-COUPLED
50mV/div
VOUT
AC-COUPLED
50mV/div
VIN
AC-COUPLED
200mV/div
VIN
AC-COUPLED
200mV/div
4µs/div
4µs/div
Pin Description
PIN
NAME
1
IN
2
GND
Ground
3
SHDN
Active-Low Shutdown Input. Connect SHDN to IN for normal operation. In shutdown, LX becomes
high impedance and quiescent current drops to 0.01µA.
FB
4
OUT
5
LX
FUNCTION
Supply Voltage Input. Input range from +2.7V to +5.5V. Bypass with a 2.2µF ceramic capacitor to
GND.
MAX1733 Voltage Feedback Input. FB regulates to 1.25V nominal. Connect FB to an external
voltage-divider between the output voltage and GND.
MAX1734 Voltage Sense Input. OUT is connected to an internal voltage-divider.
Inductor Connection
_______________________________________________________________________________________
5
MAX1733/MAX1734
Typical Operating Characteristics (continued)
(CIN = 2.2µF ceramic, COUT = 22µF tantalum, L = 10µH, unless otherwise noted.)
MAX1733/MAX1734
Low-Voltage, Step-Down DC-DC Converters
in SOT23
L1
10µH
INPUT
+2.7V TO +5.5V
IN
C1
2.2µF
VOUT
IN
LX
MAX1733
SHDN
R1
C2
22µF
MAX1733
MAX1734
CURRENT
LIMIT
FB
R2
DIGITAL
SOFT-START
GND
P
CONTROL
LOGIC
LX
N
Figure 1. MAX1733 Typical Application Circuit
SHDN
SHUTDOWN
CONTROL
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 frequency permits small, low-cost external components. Figure
2 is a simplified functional diagram.
VREF
( ) ARE FOR MAX1733 ONLY.
GND
Figure 2. Simplified Functional Diagram
Control Scheme
The MAX1733/MAX1734 use a proprietary, current-limited control scheme to ensure high-efficiency, fast transient 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 ontime 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 regulation. During this period, the low-side synchronous
rectifier turns on and remains on until either the highside switch turns on again or the inductor current
approaches zero. The internal synchronous rectifier
eliminates the need for an external Schottky diode.
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 offtime, as necessary to maintain regulation, resulting in
6
nearly constant frequency operation with high efficiency and low output voltage ripple.
Shutdown Mode
Connecting SHDN to GND places the MAX1733/
MAX1734 in shutdown mode and reduces supply current to 0.01µA. In shutdown, the control circuitry, internal 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.
Design Information
Setting the Output Voltage (MAX1733)
Select an output voltage for the MAX1733 by connecting FB to a resistive divider between the output and
_______________________________________________________________________________________
Low-Voltage, Step-Down DC-DC Converters
in SOT23
INDUCTOR VALUE
(µH)
MANUFACTURER
10
Sumida
10
Coilcraft
Table 3. Component Suppliers
PHONE
FAX
AVX
843-946-0238
843-626-3123
CR43-100
Coilcraft
847-639-6400
847-639-1469
CDRH4D18-100
Kemet
408-986-0424
408-986-1442
DT1608C-103
Murata
814-237-1431
814-238-0490
847-956-0666
847-956-0702
81-3-3607-5111
81-3-3607-5144
408-573-4150
408-573-4159
PART
NUMBER
COMPANY
Sumida
Table 2. Suggested Capacitors
CAPACITOR
TYPE
USA
Japan
Taiyo Yuden
MANUFACTURER
PART
NUMBER
Tantalum
(22µF)
Taiyo Yuden
LMK212BJ225MG
Ceramic
(2.2µF)
AVX
(
)
IOUT  VOUT VIN − OUT  1 / 2


IRMS =
VIN
TAJA226M006R
Tables 2 and 3 list some suggested capacitors and
suppliers.
GND (Figure 1). Choose R2 to be less than 50kΩ:
V

R1 = R2 ×  OUT − 1
 VREF

where VREF = 1.25V.
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 output 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 efficiency. Tables 1 and 3 list some suggested inductors
and suppliers.
Using Ceramic COUT with MAX1733
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 output 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) output 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 overshoot of the output voltage during load transients.
10µH
IN
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 switching while minimizing output ripple. Choose input and
output capacitors to filter inductor currents for acceptable voltage ripple. The input capacitor reduces peak
currents and noise at the voltage source. Input capacitors must meet the input ripple requirements and voltage rating. Use the following equation to calculate the
maximum RMS input current:
Li+
2.7V TO 4.2V
2.2µF
X7R
OUTPUT
1.8V at 250mA
LX
MAX1733
30k
2.2µF
X7R
GND
1000pF
ON
OFF
SHDN
FB
68k
Figure 3. Using a Ceramic Output Capacitor with the MAX1733
_______________________________________________________________________________________
7
MAX1733/MAX1734
Table 1. Suggested Inductors
MAX1733/MAX1734
Low-Voltage, Step-Down DC-DC Converters
in SOT23
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 gradients 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-
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.
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.
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