DC1130A - Demo Manual

DEMO CIRCUIT 1130
LT3477START
AND GUIDE
LT3003
QUICK
LT3477 and LT3003
High Current Multi-String LED Driver with
Wide PWM Dimming Range
WARNING!
DO NOT LOOK AT OPERATING LED.
This circuit produces light that can damage eyes.
DESCRIPTION
Demonstration circuit 1130 is a High Current MultiString LED Driver with Wide PWM Dimming Range
featuring the LT3477 and LT3003. The demo circuit boosts VIN, between 8V and 16V, to the required VOUT for a load of three LED strings. The
current in each string is 110mA. The LT3003 LED
ballaster offers high efficiency and good current
matching. The circuit can drive 6 to 8 white LEDs
per string. For 8 LEDs, it is recommended to
change R5 to 1.15M. For other colors, the number
of LEDs the circuit can drive depends on the forward voltage of LEDs used. The demo circuit operates at 2MHz, offering small solution size while
avoiding the frequency band of the AM radio. Pulling the SHDN terminal to ground (GND) will disable the demo board. OT1 or OT2 can be left floating.
Fast LED current turn–on and –off is made possible by adding Q1 and D2. This allows wide PWM
dimming ratio. PWM dimming offers better LED
color integrity than the DC dimming. At 100Hz
PWM frequency, 300:1 dimming ratio can be easily
achieved with this demo circuit.
Other current levels and/or load configurations can
be achieved with simple modifications. Please
consult the datasheets or the factory for customization details.
The LT3477 and the LT3003 datasheets give complete description of the part, operation and application information. The datasheets must be read in
conjunction with this quick start guide for working
on or modifying the demo circuit 1130.
Design files for this circuit board are available.
Call the LTC factory.
, LTC and LT are registered trademarks of Linear Technology Corporation.
ThinSOT and PowerPath are trademarks of Linear Technology Corporation.
PERFORMANCE SUMMARY
Specifications are at TA = 25°C
SYMBOL
VIN
VPWM
Fs
N
IOUT
VOPEN
η
PARAMETER
Input Supply Range
PWM Voltage
Switching Frequency
Number of LED Strings
Total Output Current
Open Circuit Output Voltage
Efficiency
CONDITIONS
No Load
VIN = 12V
3 LED strings, 8 LEDs per string,
110mA/string
MIN
8
3
TYP
2
3
330
29
78
MAX
16
6
UNITS
V
V
MHz
N/A
mA
V
%
1
LT3477 AND LT3003
QUICK START PROCEDURE
Demonstration circuit 1130 is easy to set up to
evaluate the performance of the LT3477 and
LT3003. Refer to Figure 1 for proper measurement
equipment setup and follow the procedure below:
NOTE. When measuring the input or output voltage ripple, care
must be taken to avoid a long ground lead on the oscilloscope
probe. Measure the input or output voltage ripple by touching the
probe tip directly across the VIN or VOUT and GND terminals. See
Figure 2 for proper scope probe technique.
4. Turn
NOTE. Make sure that the input voltage does not exceed 16V.
5. Check
power off, connect an input power supply
to VIN and GND.
2. Connect
3. Connect
the PWM turret to a different supply.
three (3) LED strings between VOUT
and LED1- to LED3- respectively.
2
for the proper voltages and currents.
NOTE. If the LEDs do not light up, check all the connections.
6. Once
the proper operations are established, adjust the input within the operating range and observe the parameters interested.
7. To
1. With
on VIN and PWM supplies.
test PWM dimming, apply a PWM signal to
the PWM turret and observe the relationship between the LED average current and the dimming ratio.
LT3477 AND LT3003
Figure 1. Proper Measurement Equipment Setup
GND
VIN
Figure 2. Measuring Input or Output Ripple
3
LT3477 AND LT3003
4
LT3477 AND LT3003
5
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