DC915A - Demo Manual

QUICK START GUIDE FOR DEMONSTRATION CIRCUIT DC915
WLED DRIVER & LCD BIAS
LT3466EDD-1
DESCRIPTION
Demonstration circuit DC915 features LT3466-1
high efficiency white LED driver and step-up converter. There is one LED driver output for 8
WLEDs and 2 normal outputs for LCD. VO1
drives 8 LEDs in series with 15mA LED current
and VO2/VO3 can delivery +/- 15V at 10mA current. If the charge-pump circuitry (C4, C5 and D1),
which generates VO3, is removed, VO2 can deliver over 35mA of current. The input voltage
range is 3V to 14V, which can go as low as 2.7V
with slightly reduced output current.
Each output channel has a jumper (JP1 or JP2)
for enabling the output(s) and a CTRL pin (CTRL1
or CTRL2) for LED brightness (current) control or
VO2/VO3 voltage adjustment. Placing the jumpers to “/SD” turns off the WLEDs or VO2/VO3, and
jumpers to “EN” enables the selected channel of
the LT3466-1. Modulating the voltage at CTRL1
or CTRL2 pin respectively can change the LED
current at VO1 or VO2/VO3 voltages. As the volt-
age on the CTRL1 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 15mA. Similarly, VO2/VO3 voltages increase with voltage on
CNTL2. The “CTRL to FB” curves are show in the
datasheet.
JP3 can conveniently set 8 WLEDs (JP3 jumper at
top position), 6 WLEDs (JP3 jumper at bottom position), or open circuit protection test (no jumper),
while FB1 terminal monitors the WLED current
(VFB1/R1).
The overall solution occupies less than 1.62 cm2
with components on one side of the PCB.
Design files for this circuit board are available.
Call the LTC factory.
________________________________________________
LT is a trademark of Linear Technology Corporation
Table 1. Performance Summary (TA = 25°C unless otherwise noted)
PARAMETER FOR LED DRIVER
CONDITION
VALUE
Minimum Input Voltage
3V
Maximum Input Voltage
14V
LED Current
With R1=13.3 ohms
15mA
VO2
15V/10mA
VO3
-14.5V/10mA
Typical Overall Efficiency
3.6V input
82%
Typical Switching Frequency
With 63.4KΩ timing resistor
800kHz
Typical Shutdown Current
3.6V input, both boost shutdown
27uA
Typical OVP at VO1
LED string open
39.5V
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QUICK START GUIDE FOR DEMONSTRATION CIRCUIT DC915
WLED DRIVER & LCD BIAS
QUICK START PROCEDURE
DC915 is easy to set up to evaluate the performance of the LT3466-1. Refer to Figure 1 for proper
measurement equipment setup and follow the procedure below:
1. With power off, connect the input power supply PS1 to VIN and GND. Make sure JP1 and JP2 are
set to “EN” positions and JP3 to “8LEDS” (default).
2. Set the input supply at 3.6V. Turn on the power at the input.
3. Observe all white LEDs light up with uniform brightness. The output voltage should measure about
26.5V, FB1 200mV, VO2 15V, and VO3 -14.5V.
4. Test the shutdown function by placing the jumper JP1 to /SD1. Observe LEDs turn off.
5. The LED brightness is controlled by DC voltage PS2 at CTRL1 terminal. With jumper removed from
JP1, observe the LED brightness change with DC voltage applied to CNTRL1 pin. The voltage range
recommended for dimming is 200mV ~ 1.6V. See the LT3466-1 data sheet for more information on
dimming control.
6. Remove PS1 and place the jumper back on JP1 at “EN1” to enable “OVP Test” of the LED string.
When jumper on JP3 is removed, VO1 shows the open circuit protection voltage (about 39.5V).
When jumper is placed to bottom terminals, only 6 WLEDs light up.
7. When JP2 is set to /SD2, VO2 goes to slightly less than Vin, and VO3 to 0. When both channels are
set to the /SD state, the total shut-down current is about 27uA at Vin=3.6V. It increases slightly with
Vin.
8. VO2 and VO3 are controlled the same way as the VFB1 vs. VCNTRL1.
Note: LT3466-1 can operate up to 22V (it needs to be 1-2V lower than output voltage for the boost converter to work
properly).
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QUICK START GUIDE FOR DEMONSTRATION CIRCUIT DC915
WLED DRIVER & LCD BIAS
Figure 1. Test Connection Diagram
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QUICK START GUIDE FOR DEMONSTRATION CIRCUIT DC915
WLED DRIVER & LCD BIAS
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