DEMO CIRCUIT 1612A-A/B
HIGH FREQUENCY SEPIC LED DRIVER
LT3519-1/LT3519-2
DESCRIPTION
Demonstration Circuit 1612A is a fully integrated LED
driver with 750mA switch current featuring the
LT®3519-1/LT3519-2. The board is optimized to
drive an LED string of up to 16V at 150mA in a SEPIC
topology. The high input voltage range, high-
efficiency low-side integrated 45V 750mA power
switch and catch diode, integrated compensation, low
voltage floating current sense amplifier, high pwm
dimming ratio, overvoltage protection, shutdown con-
trol pin, analog LED current dimming control, and
fixed 1MHz/2.2MHz switching frequency make the
LT3519-1/LT3519-2 an extremely versatile and pow-
erful high frequency LED driving IC.
DC1612A has overvoltage protection at 18V in case
the LEDs are open or not properly attached to the
terminals on the PCB. The shutdown function is acti-
vated by pulling the
SHDN/UVLO
terminal to ground.
The CTRL terminal can be used to analog dim the
LED current. The CTRL terminal is pulled up with a
resistor divider between PVIN and GND. As PVIN
drops below 7.4V, CTRL voltage drops below its full-
scale threshold and the LED current scales back.
The VIN pin is tied directly to the PVIN terminal
through R8, a zero ohm resistor. The VIN pin and ter-
minal can be separated from PVIN for some applica-
tions such as buck mode by removing R8. A few sim-
ple modifications can be made to DC1612A in order
to convert the board from a SEPIC LED driver to a
boost, buck mode, or buck-boost mode LED driver.
Please consult the datasheet for schematic details
and the factory for customization details.
The LT3519/-1/-2 datasheet gives a complete de-
scription of the part, operation and applications in-
formation. The datasheet must be read in conjunction
with this Quick Start Guide for Demonstration Circuit
1612A. The LT3519-1/-2 is assembled in a small 16-
lead plastic MSOP package. Proper board layout is
essential for maximum thermal performance. See the
datasheet section ‘Layout Considerations’.
Design files for this circuit board are available. Call
the LTC factory.
L
and
LT are registered trademarks of Linear Technology Corporation.
Table 1.
Typical Performance Summary for DC1612A-A LT3519-1
PARAMETER FOR DC1612A-A LT3519-1
PVIN=VIN Input Voltage Range
PVIN=VIN Full-Scale LED Current Input Voltage Range
Switching Frequency
LED String Current I
LED
OVP Open LED Voltage
Efficiency
Under Voltage Lockout
Low Voltage Rising Turn-On (UVLO + V
HYST
)
CONDITION
Operating
I
LED
=150mA R6=1M
LT3519-1
R1=1.69
R2=1M
R3=69.8k
R7=174k
VALUE (TYPICAL)
6V-24V
8V-24V
1MHz
150mA
18V
80.8%
6.0V
8.1V
PVIN=VIN=12V V
LED
=16V I
LED
=150mA
R4=1M
R5=261k
1
DEMO CIRCUIT 1612A-A/B
HIGH FREQUENCY SEPIC LED DRIVER
Table 2.
Typical Performance Summary for DC1612A-B LT3519-2
PARAMETER FOR DC1612A-B LT3519-2
PVIN=VIN Input Voltage Range
PVIN=VIN Full-Scale LED Current Input Voltage Range
Switching Frequency
LED String Current I
LED
OVP Open LED Voltage
Efficiency
Under Voltage Lockout
Low Voltage Rising Turn-On (UVLO + V
HYST
)
CONDITION
Operating
I
LED
=150mA R6=1M
LT3519-2
R1=1.69
R2=1M
R3=69.8k
R7=174k
VALUE (TYPICAL)
7V-24V
8V-24V
2.2MHz
150mA
18V
79.4%
7.0V
9.1V
PVIN=VIN=12V V
LED
=16V I
LED
=150mA
R4=1M
R5=215k
QUICK START PROCEDURE
DC1612A is easy to set up to evaluate the perform-
ance of the LT3519-1/LT3519-2. Follow the proce-
dure below:
EFFICIENCY
100%
90%
LT3519-1
80%
LT3519-2
70%
60%
5
10
15
INPUT VOLTAGE (V)
20
25
16V LED string
NOTE:
Make
1.
sure that the input voltage does not
exceed 24V at all times.
Connect a string of LEDs with forward voltage
less than 16V (at 150mA) to the LED+ and LED-
terminals on the PCB as shown.
With power off, connect a
6V*-24V
input power
supply to the VIN (or PVIN) and GND terminals
on the PCB.
2.
Figure 1. DC1612A Efficiency vs. PVIN 16VLED 150mA
is the minimum input voltage for
DC1612A-A.
7V
is the minimum input voltage for
DC1612A-B. 24V is the maximum input voltage for
both SEPIC applications with 16V LED and 18V
OVP.
3.
4.
NOTE:
*6V
Connect a 5V source to PWM and GND.
Turn the input power on and observe the regu-
lated LED current, the circuit efficiency, etc.
without looking directly at the LEDs.
For PWM dimming, tie a 100Hz (or higher), 5V
PWM waveform to the PWM terminal and GND
and observe the PWM dimming LED current and
PWM gate waveforms.
For shutdown, tie the
SHDN/UVLO
terminal to
GND and observe the IC turning off.
Figure 2. DC1612A-A 16VLED PWM Dimming PVIN=12V
5.
6.
2
DEMO CIRCUIT 1612A-A/B
HIGH FREQUENCY SEPIC LED DRIVER
Figure 3. DC1612A-B 16VLED PWM Dimming PVIN=12V
Figure 4. Proper Measurement Equipment Setup
3
DEMO CIRCUIT 1612A-A/B
HIGH FREQUENCY SEPIC LED DRIVER
TERMINAL OPTIONS
OPENLED
– The
OPENLED
terminal is tied directly to
the
OPENLED
pin. If there is a open LED condition, the
terminal is pulled low. When there is no fault, the ter-
minal is pulled up to VIN with a 100k resistor. This
terminal can be monitored with a voltage meter, tied to
the input of another device, or left floating.
SHDN/UVLO
– This terminal is tied directly to the
SHDN/UVLO
pin. A resistor divider from PVIN to GND
sets the voltage on this terminal/pin. These resistors
can be easily adjusted for both the UVLO level and the
amount of rising hysteresis. See the datasheet for de-
tails. The terminal can also be used to shut the IC
down and turn off the LEDs. Tie the terminal directly
to GND or place a voltage on the terminal below the
shutdown threshold of the IC in order to place the IC
in shutdown and turn off the LEDs.
CTRL
– This terminal is tied directly to the CTRL pin. A
resistor divider from PVIN to GND sets the voltage on
this terminal/pin. PVIN below 8V reduces the LED cur-
rent (analog dimming) below 150mA. The divider can
be adjusted for different analog dimming levels. Pull-
ing the CTRL pin to GND turns the LEDs off. An exter-
nal voltage applied to the CTRL terminal can reduce
the LED current. See the datasheet for analog dim-
ming details. It is okay to float this terminal.
PWM
– This terminal is tied directly to the PWM pin
and to the gate of the N-Channel MOSFET in series
with the LED string. M1 requires a 5V gate drive for
proper operation, but a lower voltage MOSFET can be
used in its place. PWM dimming performance of the
LT3519-1/-2 is discussed in the datasheet. Make sure
to supply a proper PWM dimming voltage, frequency,
and duty cycle to the LT3519-1/-2 SEPIC application.
If PWM dimming is not used, the PWM terminal can
be tied directly to a 5V DC source. If this terminal is
left unconnected, the LEDs will not turn on.
VIN and PVIN
– VIN is tied directly to the VIN pin of
the IC. PVIN is tied directly to the inductor. The two
are shorted together with a zero ohm resistor R8. R8
can be removed and VIN can be powered separately
from PVIN or VIN can be tied directly to the OUT ter-
minal for buck mode operation with resistor option
R14.
4
DEMO CIRCUIT 1612A-A/B
HIGH FREQUENCY SEPIC LED DRIVER
5
京公网安备 11010802033920号
EEWORLD
