LM3424 Datasheet, PDF (2/50 Pages) National Semiconductor (TI) – Constant Current N-Channel Controller with Thermal Foldback for Driving LEDs

Connection Diagram
20-Lead TSSOP EP
30085704
Ordering Information
Order Number Spec.
Package Type
LM3424MH
LM3424MHX
NOPB
NOPB
Pin Descriptions
TSSOP-20 EP
TSSOP-20 EP
NSC Package
Drawing
MXA20A
MXA20A
Supplied As
73 Units, Rail
2500 Units, Tape and Reel
Pin
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
DAP
Name
V_IN
EN
COMP
CSH
RT
nDIM
SS
TGAIN
TSENSE
TREF
V_S
OVP
DDRV
GND
GATE
V_CC
IS
SLOPE
HSN
HSP
DAP
Description
Input Voltage
Enable
Compensation
Current Sense High
Resistor Timing
Dimming Input /
Under-Voltage Protection
Soft-start
Temp Foldback Gain
Temp Sense Input
Temp Foldback Reference
Voltage Reference
Over-Voltage Protection
Dimming Gate Drive Output
Ground
Main Gate Drive Output
Internal Regulator Output
Main Switch Current Sense
Slope Compensation
LED Current Sense Negative
LED Current Sense Positive
Thermal pad on bottom of IC
Application Information
Bypass with 100 nF capacitor to GND as close to the device as possible.
Connect to > 2.4V to enable the device or to < 0.8V for low power shutdown.
Connect a capacitor to GND to compensate control loop.
Connect a resistor to GND to set the signal current. Can also be used to analog
dim as explained in the Thermal Foldback / Analog Dimming section.
Connect a resistor to GND to set the switching frequency. Can also be used
to synchronize external clock as explained in the Switching Frequency section.
Connect a PWM signal for dimming as detailed in the PWM Dimming section
and/or a resistor divider from V_IN to program input under-voltage lockout.
Connect a capacitor to GND to extend start-up time.
Connect a resistor to GND to set the foldback slope.
Connect a resistor/ thermistor divider from V_S to sense the temperature as
explained in the Thermal Foldback / Analog Dimming section.
Connect a resistor divider from V_S to set the foldback reference voltage.
2.45V reference for temperature foldback circuit and other external circuitry.
Connect a resistor divider from V_O to program output over-voltage lockout.
Connect to gate of dimming MosFET.
Connect to DAP to provide proper system GND
Connect to gate of main switching MosFET.
Bypass with a 2.2 µF – 3.3 µF, ceramic capacitor to GND.
Connect to the drain of the main N-channel MosFET switch for R_DS-ON sensing
or to a sense resistor installed in the source of the same device.
Connect a resistor to GND to set slope of additional ramp.
Connect through a series resistor to LED current sense resistor (negative).
Connect through a series resistor to LED current sense resistor (positive).
Connect to GND. Refer to (Note 4) for thermal considerations.
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