LM3424 Datasheet, PDF (9/50 Pages) National Semiconductor (TI) – Constant Current N-Channel Controller with Thermal Foldback for Driving LEDs

Block Diagram
Theory of Operation
The LM3424 is an N-channel MosFET (NFET) controller for
buck, boost and buck-boost current regulators which are ideal
for driving LED loads. The controller has wide input voltage
range allowing for regulation of a variety of LED loads. The
high-side differential current sense, with low adjustable
threshold voltage, provides an excellent method for regulating
output current while maintaining high system efficiency. The
LM3424 uses peak current mode control providing good noise
immunity and an inherent cycle-by-cycle current limit. The
adjustable current sense threshold provides the capability to
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amplitude (analog) dim the LED current and the thermal fold-
back circuitry allows for precise temperature management of
the LEDs. Tthe output enable/disable function coupled with
an internal dimming drive circuit provides high speed PWM
dimming through the use of an external MosFET placed at the
LED load. When designing, the maximum attainable LED cur-
rent is not internally limited because the LM3424 is a con-
troller. Instead it is a function of the system operating point,
component choices, and switching frequency allowing the
LM3424 to easily provide constant currents up to 5A. This
simple controller contains all the features necessary to im-
plement a high efficiency versatile LED driver.
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