DC723A - Demo Manual

QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 723
DUAL HIGH EFFICIENCY WHITE LED (7/10) DRIVER
LT3466EDD
DESCRIPTION
Demonstration circuit 723 features the LT®3466 dual
high efficiency white LED driver. There are two LED
driver outputs on DC723. Vout1 drives 10 LEDs and
Vout2 drives 7 LEDs in series with 12mA LED current. Both outputs are generated from a 3~8V input
(or 3~20V with diode option).
Each output channel has a jumper for enabling the
LED output (JP1, JP2) and a CTRL pin (CTRL1,
CTRL2) for LED brightness (current) control. Placing
the jumper to “SHDN” turns off the selected LED
channel and jumper to “Enable” enables the selected
LED channel of the LT3466. Modulating the voltage
at CTRL1 and CTRL2 pins respectively can change
the LED current in the two drivers. As the voltage on
the CTRL pin increases from 0V to 1.6V, the feedback
voltage across the LED current programming resistor
increases from 0 to 200mV varying the LED current
from 0 to 12mA. The feedback voltage variation versus control voltage is shown in Figure 1.
Design files for this circuit board are available. Call
the LTC factory.
LT is a registered trademark of Linear Technology Corporation
Table 1. Performance Summary ( TA = 25°C )
PARAMETER FOR LED DRIVER
CONDITION
VALUE
Minimum Input Voltage
Maximum Input Voltage
3V
(20V with optional diode)
LED Current
8V
12mA
Typical Efficiency
With 8V input
82%
Typical Switching Frequency
With 147KΩ timing resistor
350kHz
QUICK START PROCEDURE
Demonstration circuit 723 is easy to set up to evaluate the performance of the LT3466. Refer to Figure 2.
for proper measurement equipment setup and follow
the procedure below:
1. With power off, connect the input power supply to Vin and GND. Make sure JP1 and JP2
are set to “ENABLE”.
2. Set the input supply between 3V to 8V. Turn
on the power at the input.
3. Observe all white LEDs light up with uniform
brightness. The output voltage should measure about 23V for 7 LEDs and 33V for 10
LEDs across the “Vout Test” terminal to
“GND” terminal.
output and JP2 controls the 7 LED output.
Observe the LEDs turn off with each jumper
move to SHDN.
5. The LED brightness is controlled by DC voltage at the CTRL terminal. With JP1 (or JP2)
placed at SHDN, observe the LED brightness
change with DC voltage applied to the CTR1
(or CTR2) pin. The voltage range recommended for dimming is 200mV ~ 1.6V. See
the LT3466 data sheet for more information
on CTRL dimming control.
6. Place JP1 (or JP2) back to “ENABLE” to enable the “Vout1 Test” (or “Vout2 Test”) LED
string.
4. Test the shutdown function by placing the
jumper to SHDN. JP1 controls the 10 LED
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QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 723
DUAL HIGH EFFICIENCY WHITE LED (7/10) DRIVER
Note: LT3466 can operate up to 20V input with an optional diode (D18 on the backside of the DC723 board).
The diode is used to protect the internal Schottky diode during startup.
Figure 1.
VFB1,2 vs VCTRL1,2
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QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 723
DUAL HIGH EFFICIENCY WHITE LED (7/10) DRIVER
Figure 2. Proper Measurement Equipment Setup
Figure 3. Scope Probe Placement for Measuring Input or Output Ripple
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QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 723
DUAL HIGH EFFICIENCY WHITE LED (7/10) DRIVER
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