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PDF LM2733 Data sheet ( Hoja de datos )

Número de pieza LM2733
Descripción 0.6/1.6 MHz Boost Converters With 40V Internal FET
Fabricantes National Semiconductor 
Logotipo National Semiconductor Logotipo




1. LM2733






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No Preview Available ! LM2733 Hoja de datos, Descripción, Manual

February 2003
LM2733
0.6/1.6 MHz Boost Converters With 40V Internal FET
Switch in SOT-23
General Description
The LM2733 switching regulators are current-mode boost
converters operating fixed frequency of 1.6 MHz (“X” option)
and 600 kHz (“Y” option).
The use of SOT-23 package, made possible by the minimal
power loss of the internal 1A switch, and use of small induc-
tors and capacitors result in the industry’s highest power
density. The 40V internal switch makes these solutions per-
fect for boosting to voltages of 16V or greater.
These parts have a logic-level shutdown pin that can be
used to reduce quiescent current and extend battery life.
Protection is provided through cycle-by-cycle current limiting
and thermal shutdown. Internal compensation simplifies de-
sign and reduces component count.
Switch Frequency
X
1.6 MHz
Y
0.6 MHz
Features
n 40V DMOS FET switch
n 1.6 MHz (“X”), 0.6 MHz (“Y”) switching frequency
n Low RDS(ON) DMOS FET
n Switch current up to 1A
n Wide input voltage range (2.7V–14V)
n Low shutdown current (<1 µA)
n 5-Lead SOT-23 package
n Uses tiny capacitors and inductors
n Cycle-by-cycle current limiting
n Internally compensated
Applications
n White LED Current Source
n PDA’s and Palm-Top Computers
n Digital Cameras
n Portable Phones and Games
n Local Boost Regulator
Typical Application Circuit
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20055401
© 2003 National Semiconductor Corporation DS200554
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www.national.com

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LM2733 pdf
Typical Performance Characteristics Unless otherwise specified: VIN = 5V, SHDN pin is tied to VIN.
Iq VIN (Active) vs Temperature - "X"
Iq VIN (Active) vs Temperature - "Y"
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Oscillator Frequency vs Temperature - "X"
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Oscillator Frequency vs Temperature - "Y"
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Max. Duty Cycle vs Temperature - "X"
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Max. Duty Cycle vs Temperature - "Y"
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5
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LM2733 arduino
Application Hints (Continued)
MAXIMUM SWITCH CURRENT
The maximum FET swtch current available before the cur-
rent limiter cuts in is dependent on duty cycle of the appli-
cation. This is illustrated in the graphs below which show
both the typical and guaranteed values of switch current for
both the "X" and "Y" versions as a function of effective
(actual) duty cycle:
The equation shown to calculate maximum load current
takes into account the losses in the inductor or turn-OFF
switching losses of the FET and diode. For actual load
current in typical applications, we took bench data for vari-
ous input and output voltages for both the "X" and "Y"
versions of the LM2733 and displayed the maximum load
current available for a typical device in graph form:
20055425
Switch Current Limit vs Duty Cycle - "X"
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Max. Load Current vs VIN - "X"
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Switch Current Limit vs Duty Cycle - "Y"
CALCULATING LOAD CURRENT
As shown in the figure which depicts inductor current, the
load current is related to the average inductor current by the
relation:
ILOAD = IIND(AVG) x (1 - DC)
Where "DC" is the duty cycle of the application. The switch
current can be found by:
ISW = IIND(AVG) + 12 (IRIPPLE)
Inductor ripple current is dependent on inductance, duty
cycle, input voltage and frequency:
IRIPPLE = DC x (VIN-VSW) / (f x L)
combining all terms, we can develop an expression which
allows the maximum available load current to be calculated:
20055433
Max. Load Current vs VIN - "Y"
DESIGN PARAMETERS VSW AND ISW
The value of the FET "ON" voltage (referred to as VSW in the
equations) is dependent on load current. A good approxima-
tion can be obtained by multiplying the "ON Resistance" of
the FET times the average inductor current.
FET on resistance increases at VIN values below 5V, since
the internal N-FET has less gate voltage in this input voltage
range (see Typical performance Characteristics curves).
Above VIN = 5V, the FET gate voltage is internally clamped
to 5V.
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