DEMO CIRCUIT 1482
FULLY INTEGRATED LED DRIVER
LT3519
DESCRIPTION
Demonstration Circuit 1482 is a fully integrated
LED driver with 750mA switch current featuring
the LT®3519. The board is optimized to drive a
100mA LED string between the input voltage
and 38V in a boost topology. The high input
voltage range, high-efficiency low-side inte-
grated 45V 750mA power switch and catch di-
ode, integrated compensation, low voltage float-
ing current sense amplifier, high pwm dimming
ratio, overvoltage protection, shutdown control
pin, analog LED current dimming control, and
fixed 400kHz switching frequency make the
LT3519 an extremely versatile and powerful
LED driving IC.
DC1482 has overvoltage protection at just
above 40V if the LEDs are open or not properly
attached to the terminals on the PCB. The
shutdown function is activated by pulling the
shutdown terminal to ground. Shutdown turns
off the IC, but still allows the input voltage to be
seen at the output. The LEDs can leak small
current if VIN is high enough to turn them on
during shutdown. The CTRL terminal can be
used to analog dim the LED current. The CTRL
terminal is pulled up with a resistor divider be-
tween VIN and GND. As VIN drops too low,
CTRL voltage drops and the LED current is
scaled back.
The VIN pin is tied directly to PVIN through a
zero ohm resistor. The VIN pin and terminal can
be separated from PVIN for some applications
such as buck mode by removing this zero ohm
resistor. A few simple modifications can be
made to DC1482 in order to convert the board
from a boost LED driver to a SEPIC, buck
mode, or buck-boost mode LED driver. Please
consult the datasheet for schematic details and
the factory for customization details.
The LT3519 datasheet gives a complete de-
scription of the part, operation and applications
information. The datasheet must be read in
conjunction with this Quick Start Guide for
demonstration circuit 1482. The LT3519 is as-
sembled in a small 16-lead plastic MSOP pack-
age. Proper board layout is essential for maxi-
mum thermal performance. See the datasheet
section ‘Layout Considerations’.
Design files for this circuit board are avail-
able. Call the LTC factory.
LT is a trademark of Linear Technology Corporation
2.
QUICK START PROCEDURE
DC1482 is easy to set up to evaluate the per-
formance of the LT3519. Follow the procedure
below:
NOTE:
Make
1.
3.
4.
With power off, connect a 6V-30V input
power supply to the VIN (or PVIN) and
GND terminals on the PCB. Make sure that
VIN does not exceed the voltage of the LED
string.
Connect a 3.3V source to PWM and GND.
Turn the input power on and observe the
regulated LED current, the circuit efficiency,
etc. without looking directly at the LEDs.
For PWM dimming, tie a 100Hz (or higher),
3-5V PWM waveform to the PWM terminal
and GND and observe the PWM dimming
LED current and PWM gate waveforms.
sure that the input voltage does
not exceed 40V at all times and 30V DC.
Connect a string of LEDs with forward volt-
age less than 38V, but greater than the in-
put voltage, to the LED+ and LED- termi-
nals on the PCB as shown.
5.
1
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