DC637A - Demo Manual

QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 637
SINGLE CELL WHITE LED (4) DRIVER
LT3465/LT3465A
DESCRIPTION
Demonstration circuit 637 features the LT®3465 and
LT®3465A constant-current white LED drivers in
small SOT23 ThinSOT packages. The demo board is
designed to demonstrate high efficiency and small
size performance of the LT3465 and LT3465A, made
possible by a 200mV feedback voltage, 1.2MHz
(2.4MHz for LT3465A) switching frequency, and a
special internal compensation network allowing 0603
input/output capacitors (the output capacitor at
0.22uF). The DC637 is specifically designed for white
LED backlight applications using 2~4 LEDs, making
the LT3465 an ideal solution for battery powered
portable applications such as cellular phone, digital
camera, MP3 player, GPS receiver, and handheld
computer (PDAs). LT3465 offers numerous LEDdimming circuit options, see the datasheet for more
detailed information on LED brightness control.
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 = 25oC )
PARAMETER FOR LED DRIVER
CONDITION
VALUE
Output Voltage
VIN = 2.7V ~ 5V
~13V
Typical Output Ripple
VIN = 3.6V, ILED = 15mA
~30mV
Typical Efficiency
VIN = 3.6V, ILED = 15mA
80%
QUICK START PROCEDURE
DC637 is easily set up for evaluating the LT3465 and
LT3465A low noise constant-current step-up LED
driver circuit. Follow the test procedure outlined
below and see Figure1.
1. There are two LED driver circuits on DC637.
The two circuits are named “Efficiency” and
“Size”. Placing the JP2 jumper to “Efficiency”
enables the more efficient LT3465 circuit and
placing JP2 jumper to “Size” enables the
smaller LT3465A circuit. Place the JP2 jumper
on “Efficiency” to test the LT3465 circuit. If
you want to test “Size” circuit, go to step 6.
2. The demo circuit can be powered from a 3V
Lithium battery installed on the demo board
(BT1) or other input source (bench top power
supply) by selecting input source jumper
(JP1). For battery (BT1) input operation,
place the jumper (JP1) to “BATTERY” position
and go to step 4.
3. For bench supply input, place the jumper
(JP1) in the “Vin” position and connect a
3.3V, 500mA bench supply to the Vin and Gnd
terminals.
4. Turn on the input power supply or connect the
single cell Li-Ion battery. Turn on the LT3465
LED driver circuit by pressing SW1. Observe
all four white LEDs light up with uniform
brightness.
The output voltage should
measure about 13V across the “Vout Test”
terminal to “Gnd” terminal.
5. The led brightness is controlled by the DC
voltage at the CTRL terminal. The typical DC
voltage range recommended for dimming is
200mV~ 1.5V. See the LT3465 data sheet for
more information on CTRL dimming control.
6. Place the jumper on “Size” to test the
LT3465A circuit.
7. The demo board can be powered from a 3V
Lithium battery installed on the demo board
(BT1) or other input source (bench top power
supply) by selecting input source jumper
1
QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 637
SINGLE CELL WHITE LED (4) DRIVER
(JP1). For battery (BT1) input operation, place
the jumper (JP1) to “BATTERY” position and
go to step 9.
brightness. The output voltage should
measure about 13V across the “Vout Test”
terminal to “Gnd” terminal.
8. For bench supply input, place the jumper
(JP1) in the “Vin” position and connect a
3.3V, 500mA bench supply to the Vin and Gnd
terminals.
10. The LED brightness is controlled by a PWM
signal at the CTRL terminal. The typical
frequency range recommended for PWM
dimming is 1kHz~10kHz with a signal
magnitude of 2V. See the LT3465A data sheet
for more information on CTRL dimming
control.
9. Turn on the input power supply or connect the
single cell Li-Ion battery. Turn on the LT3465A
LED driver circuit by pressing SW2. Observe
all four white LEDs light up with uniform
Figure 1. Proper Measurement Equipment Setup
Figure 2. Scope Probe Placement for Measuring Input or Output Ripple
2
QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 637
SINGLE CELL WHITE LED (4) DRIVER
3
QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 637
SINGLE CELL WHITE LED (4) DRIVER
4
Similar pages