DC1288A - Demo Manual

DEMO CIRCUIT 1288
LT3496EUFD
QUICK START
GUIDE
DESCRIPTION
WARNING!
Do not look directly at operating LED.
This circuit produces light that can damage
eyes.
Demonstration circuit 1288 is a Triple Boost or
Buck-Boost
LED
Driver
featuring
the
LT3496EUFD. The LT3496 is a triple output
DC/DC converter designed to operate as
current sources for driving high current LEDs.
For evaluating an LT3496 buck mode LED
driver, use the demonstration circuit 986.
The board can be configured into either buckboost (default) or boost mode. The current for
each output is set at 200mA in either mode. The
targeted input voltage PVIN range is 8V to 16V.
The buck-boost circuit can tolerate an input
voltage up to 40V when the LED string is on the
high side. The part shuts down when the overvoltage threshold is reached. For a typical
application with 5 LEDs totaling of 16V LED
voltage, the circuit will operate until PVIN
reaches 22V if the over-voltage protection is set
to 38V. The buck-boost circuit with LEDs on the
low side may not survive a 40V input transient.
Applications with different input voltages and
LT3496EUFD
Triple Boost or Buck-Boost
LED Driver
load combinations can be demonstrated on this
circuit with some board modifications. Call the
LTC applications group for support.
Each of the three regulators on the demo board
is independently operated. The PWM dimming
feature of the LT3496 allows True Color PWM
dimming with the dimming ratio of 5000:1.
Additional analog dimming is possible.
Setting CTRL voltage to be less than 1V will set
the current sense voltage to be one-tenth of
CTRL voltage, therefore, reduce the LED
current. The output current should not exceed
the rated current of the LEDs used. The LED
current thermal de-rating should be considered
to protect the LEDs. Adjustable switching
frequency allows optimization of the efficiency
and the external component size.
The LT3496 datasheet gives complete
description of the part, operation and application
information. The datasheet must be read in
conjunction with this quick start guide for
working on or modifying the demo circuit 986.
Design files for this circuit board are
available. Call the LTC factory.
, LTC and LT are registered trademarks of Linear Technology Corporation.
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LT3496EUFD
PERFORMANCE SUMMARY Specifications are at TA = 25°C
SYMBOL PARAMETER
PVIN
Power Input Supply
CONDITIONS
Buck-Boost Mode (LEDs on High Side)
Boost Mode
VIN
Chip Bias Input Supply**
VOVP
ILED
FSW
Output Over-voltage Protection
Output LED Current, per Channel
Switching Frequency
Conversion Efficiency
η
PWMD
PWM Dimming Ratio
FADJ=VREF
Buck-Boost Mode: ILED = 200mA, PVIN=12V,
VIN=3.3V, 5 LEDs
Boost Mode: ILED = 200mA, PVIN=12V,
VIN=3.3V, 7 LEDs
PWM Frequency: 100Hz
MIN
8
8
3
TYP
188
1.9
196
2.1
80
MAX
40
VLED*
5.5
38
204
2.3
UNITS
V
V
V
mA
MHz
%
90
5000:1
* VLED is the forward voltage drop of a LED string
** VIN of the demo board is limited by the choice of the input capacitor. The LT3496 input range is
3V-30V with transient protection to 40V. A lower VIN helps to reduce the power dissipation in the chip.
MODE SETUP
JP3, JP4, JP5 C2, C6, C8
Buck-Boost =Buck-Boost Not Install
C11, C12, C13
Install
Boost
Not Install
=Boost
Install
LED on High Side
Short LEDnL+ and
LEDnLN/A
LED on Low Side
Short
LEDnH+
and LEDnHShort
LEDnH+
and LEDnH-
QUICK START PROCEDURE
Demonstration circuit 1288 is easy to set up to
evaluate the performance of the LT3496EUFD.
Refer to Figure 1 for proper measurement
equipment setup and follow the procedure
below:
2. Connect an input power supply to VIN and
GND. To achieve highest efficiency, a low
voltage supply, such as 3.3V or 5V, is
recommended.
1. With power off, select buck-boost or boost
mode. Setup the board per the table in the
“MODE SETUP” section. The default setting
is for buck-boost mode.
4. If an output channel n is not used, the PWMn
should be tied to GND.
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3. With power off, connect a second input power
supply to PVIN and GND.
5. Turn on PVIN power supply.
6. Turn on VIN power supply.
LT3496EUFD
7. Check for the proper LED current and LED
string voltage.
NOTE. If there is no output, turn off the power supplies.
Check all connections.
8. To observe PWM dimming, turn off all power
supplies. Connect the PWMn to a pulse
generator. Then repeat step 5 – 7.
Figure 1. Proper Measurement Equipment Setup (LEDs on the High Side)
Figure 2. Proper Measurement Equipment Setup (LEDs on the Low Side)
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LT3496EUFD
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