DC1405A - Demo Manual

DEMO CIRCUIT 1405
LT3492
QUICK START GUIDE
LT3492
Triple Boost or Buck/Boost
LED Driver
DESCRIPTION
WARNING!
Do not look directly at operating LED.
This circuit produces light that can damage eyes.
Demonstration circuit 1405 is a Triple Boost or
Buck/Boost LED Driver featuring the LT3492. The
LT3492 is a triple output DC/DC converter designed to
operate as current sources for driving LEDs.
The board can be configured into either boost (default)
or buck-boost mode. The current for each output is
61mA in either mode. The over-voltage protection is
at 58V. For a typical application with a LED voltage of
3.6V, each boost circuit can drive around 15 LEDs.
Applications with different input voltages and load
combinations can be demonstrated on this circuit with
some board modifications. Call the LTC applications
group for support.
the LT3492 allows True Color PWM dimming with the
dimming ratio of 3000:1. Additional analog dimming
is done through adjusting the CTRL voltages.
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.
The LT3492 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 1405.
Design files for this circuit board are available. Call
the LTC factory.
, LTC and LT are registered trademarks of Linear Technology Corporation. All other
trademarks are the property of their respective owners
Each of the three regulators on the demo board is independently operated. The PWM dimming feature of
PERFORMANCE SUMMARY Specifications are at TA = 25°C
SYMBOL
PVIN
PARAMETER
Power Input Supply*
VIN
Chip Bias Input Supply**
IQ
Quiescent Current at VIN
VOVP
ILED
FSW
η
Output Over-voltage Protection
Output LED Current, per Channel
Switching Frequency
Conversion Efficiency
PWMD
PWM Dimming Ratio
CONDITIONS
Boost Mode, ILED = 61mA, LED String Voltage =
48V.
MIN
8
TYP
MAX
40
4.5
5
5.5
Boost Mode, ILED = 61mA, PVIN=12V, VIN=5V, LED
String Voltage = 48V.
29
59
0.77
Boost Mode, ILED = 61mA, PVIN=12V, VIN=5V, LED
String Voltage = 48V.
PWM Frequency: 100Hz
58.7
61
1
85
UNITS
V
V
mA
63
1.23
V
mA
MHz
%
3000:1
* MIN and MAX PVIN are determined by switch current limit, minimum/maximum duty cycle, output voltage, etc.
** 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.
1
LT3492
QUICK START PROCEDURE
Demonstration circuit 1405 is easy to set up to evaluate the performance of the LT3492. Refer to 0 for
proper measurement equipment setup and follow the
procedure below:
1. Make sure JP4=ON. With power off, select boost or
buck/boost mode. The default setting is for boost
mode. If buck/boost mode is selected, also remove
C2, C4, C6 and populate C1, C3, C5.
2. Connect an input power supply to VIN and GND. To
achieve highest efficiency, a low voltage supply,
such as 5V, is recommended.
3. With power off, connect a second input power supply to PVIN and GND.
4. Connect LED strings as shown in Figure 1.
5. If LED string n is not used, the PWMn should be
tied to GND.
6. Turn on PVIN power supply.
7. Turn on VIN power supply.
8. Check for the proper LED current and LED string
voltage.
NOTE. If there is no output, turn off the power supplies. Check all
connections.
9. To observe PWM dimming, turn off all power supplies. Connect the PWMn to a pulse generator.
Then repeat step 6 – 8.
Figure 1. Proper Measurement Equipment Setup (LEDs on the High Side)
2
LT3492
3
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