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MAX1735EUK50+ ,200mA, Negative-Output, Low-Dropout Linear Regulator in SOT23FeaturesThe MAX1735 negative-output, low-dropout linear regu-♦ Guaranteed 200mA Output Currentlator ..
MAX4563EEE+ ,Serially Controlled, Clickless Audio/Video SwitchesELECTRICAL CHARACTERISTICS—Single +5V Supply(V+ = +5V ±5%, T = T to T , unless otherwise noted. Typ ..
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MAX1733EUK-MAX1733EUK-T
Low-Voltage / Step-Down DC-DC Converters in SOT23
General DescriptionThe 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.
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.
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.
ApplicationsCellular, PCS, and Cordless Telephones
PDAs, Palmtops, and Handy-Terminals
Battery-Powered Equipment
Features250mA Guaranteed Output CurrentSynchronous Rectifier for Over 90% EfficiencyTiny 5-Pin SOT23 Package40µA Quiescent Supply Current0.01µA Logic-Controlled ShutdownUp to 1.2MHz Switching FrequencyFixed 1.8V or 1.5V Outputs (MAX1734)Adjustable Output Voltage (MAX1733)±1.5% Initial Accuracy2.7V to 5.5V Input RangeSoft-Start Limits Startup Current
MAX1733/MAX1734
Low-Voltage, Step-Down DC-DC Converters
in SOT23
Pin Configurationypical Operating Circuit19-1586; Rev 0; 7/00
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.
Ordering Information MAX1733/MAX1734
Low-Voltage, Step-Down DC-DC Converters
in SOT23
ABSOLUTE MAXIMUM RATINGS
ELECTRICAL CHARACTERISTICSStresses 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.
IN, SHDNto 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
MAX1733/MAX1734
Low-Voltage, Step-Down DC-DC Converters
in SOT23
Note 1:All devices are 100% production tested at TA= +25°C. Limits over the operating temperature range are guaranteed by design.
ELECTRICAL CHARACTERISTICS
MAX1733/MAX1734
Low-Voltage, Step-Down DC-DC Converters
in SOT23
Typical Operating Characteristics(CIN= 2.2µF ceramic, COUT= 22µF tantalum, L = 10µH, unless otherwise noted.)
MAX1733/MAX1734
Low-Voltage, Step-Down DC-DC Converters
in SOT23
Typical Operating Characteristics (continued)(CIN= 2.2µF ceramic, COUT= 22µF tantalum, L = 10µH, unless otherwise noted.)
Pin Description
MAX1733/MAX1734
Detailed DescriptionThe 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.
Control SchemeThe 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.
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
nearly constant frequency operation with high efficien-
cy and low output voltage ripple.
Shutdown ModeConnecting SHDNto 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 SHDNto IN
for normal operation.
Soft-StartThe 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 Characteristicssection.
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
Low-Voltage, Step-Down DC-DC Converters
in SOT23
