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PDF LM2736XMK Data sheet ( Hoja de datos )

Número de pieza LM2736XMK
Descripción Thin SOT23 750mA Load Step-Down DC-DC Regulator
Fabricantes National Semiconductor 
Logotipo National Semiconductor Logotipo



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No Preview Available ! LM2736XMK Hoja de datos, Descripción, Manual

October 2004
LM2736
Thin SOT23 750mA Load Step-Down DC-DC Regulator
General Description
The LM2736 regulator is a monolithic, high frequency, PWM
step-down DC/DC converter in a 6-pin Thin SOT23 package.
It provides all the active functions to provide local DC/DC
conversion with fast transient response and accurate regu-
lation in the smallest possible PCB area.
With a minimum of external components and online design
support through WEBENCH, the LM2736 is easy to use.
The ability to drive 750mA loads with an internal 350m
NMOS switch using state-of-the-art 0.5µm BiCMOS technol-
ogy results in the best power density available. The world
class control circuitry allows for on-times as low as 13ns,
thus supporting exceptionally high frequency conversion
over the entire 3V to 18V input operating range down to the
minimum output voltage of 1.25V. Switching frequency is
internally set to 550kHz (LM2736Y) or 1.6MHz (LM2736X),
allowing the use of extremely small surface mount inductors
and chip capacitors. Even though the operating frequencies
are very high, efficiencies up to 90% are easy to achieve.
External shutdown is included, featuring an ultra-low
stand-by current of 30nA. The LM2736 utilizes current-mode
control and internal compensation to provide high-
performance regulation over a wide range of operating con-
ditions. Additional features include internal soft-start circuitry
to reduce inrush current, pulse-by-pulse current limit, ther-
mal shutdown, and output over-voltage protection.
Features
n Thin SOT23-6 package
n 3.0V to 18V input voltage range
n 1.25V to 16V output voltage range
n 750mA output current
n 550kHz (LM2736Y) and 1.6MHz (LM2736X)
switching frequencies
n 350mNMOS switch
n 30nA shutdown current
n 1.25V, 2% internal voltage reference
n Internal soft-start
n Current-Mode, PWM operation
n WEBENCH online design tool
Applications
n Local Point of Load Regulation
n Core Power in HDDs
n Set-Top Boxes
n Battery Powered Devices
n USB Powered Devices
n DSL Modems
n Notebook Computers
Typical Application Circuit
Efficiency vs Load Current "X"
VIN = 5V, VOUT = 3.3V
20124201
WEBENCHis a trademark of Transim.
© 2004 National Semiconductor Corporation DS201242
20124251
www.national.com

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LM2736XMK pdf
Typical Performance Characteristics All curves taken at VIN = 5V, VBOOST - VSW = 5V, L1 = 4.7 µH
("X"), L1 = 10 µH ("Y"), and TA = 25˚C, unless specified otherwise. (Continued)
Oscillator Frequency vs Temperature - "X"
Oscillator Frequency vs Temperature - "Y"
20124255
Current Limit vs Temperature
VIN = 18V, VIN = 5V
VFB vs Temperature
20124228
RDSON vs Temperature
20124229
20124233
IQ Switching vs Temperature
20124230
5
20124246
www.national.com

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LM2736XMK arduino
Design Guide (Continued)
OUTPUT VOLTAGE
The output voltage is set using the following equation where
R2 is connected between the FB pin and GND, and R1 is
connected between VO and the FB pin. A good value for R2
is 10k.
PCB Layout Considerations
When planning layout there are a few things to consider
when trying to achieve a clean, regulated output. The most
important consideration when completing the layout is the
close coupling of the GND connections of the CIN capacitor
and the catch diode D1. These ground ends should be close
to one another and be connected to the GND plane with at
least two through-holes. Place these components as close to
the IC as possible. Next in importance is the location of the
GND connection of the COUT capacitor, which should be
near the GND connections of CIN and D1.
There should be a continuous ground plane on the bottom
layer of a two-layer board except under the switching node
island.
The FB pin is a high impedance node and care should be
taken to make the FB trace short to avoid noise pickup and
inaccurate regulation. The feedback resistors should be
placed as close as possible to the IC, with the GND of R2
placed as close as possible to the GND of the IC. The VOUT
trace to R1 should be routed away from the inductor and any
other traces that are switching.
High AC currents flow through the VIN, SW and VOUT traces,
so they should be as short and wide as possible. However,
making the traces wide increases radiated noise, so the
designer must make this trade-off. Radiated noise can be
decreased by choosing a shielded inductor.
The remaining components should also be placed as close
as possible to the IC. Please see Application Note AN-1229
for further considerations and the LM2736 demo board as an
example of a four-layer layout.
11 www.national.com

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