LM3424 Datasheet, PDF (11/69 Pages) National Semiconductor (TI) – Constant Current N-Channel Controller with Thermal Foldback for Driving LEDs

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7 Detailed Description
LM3424, LM3424-Q1
SNVS603C – AUGUST 2009 – REVISED AUGUST 2015
7.1 Overview
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 amplitude (analog) dim the LED current and the thermal
foldback circuitry allows for precise temperature management of the LEDs. The 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 current is not internally limited
because the LM3424 is a controller. 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 implement a high efficiency versatile LED driver.
7.2 Functional Block Diagram
V_IN
EN
820k
UVLO
HYSTERESIS
nDIM
1.24V
20 2A
6.9V LDO
Regulator
UVLO ^{VCC UVLO}
(4.1V)
TLIM _Thermal
Limit
Dimming
RT
SLOPE
COMP
CSH
Clock
Artificial Ramp
Oscillator
LEB
9 = 240 ns
1.24V
PWM
HSP
HSN
IS
LEB
90k _{10 2A}
1.7k
CURRENT
LIMIT
0.245V
10 2A
SS
COMP
STANDBY
1.24V
REFERENCE
Standby
V_CC
OVLO
Reset
Dominant
SQ
R
V_CC
20 2A
OVP
HYSTERESIS
OVLO
1.24V
1.24V
100k
100k
100k 100k
100k 100k
V_CC
DDRV
GATE
GND
OVP
VS
TREF
TSENSE
TGAIN
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