DC986A - Demo Manual

DEMO CIRCUIT 9 8 6
LT3496EUFD
Q UICK S TA
RT G UIDE
L T3 4 9 6 EUF D
Trip le S te p -Do w n L ED Driv e r
DESCRIPTION
WARNING!
Do not look directly at operating LED.
This circuit produces light that can damage eyes.
Demonstration circuit 986 is a Triple Step-Dow n LED
Driver featuring the LT3496EU FD. The LT3496 is a
triple output DC/DC converter designed to operate as
current sources for driving high current LEDs. O n the
demo board, the default current for each output channel is 500mA. Setting CTR L voltage to be less than 1V
w ill control the current sense voltage to be one-tenth
of CTR L voltage, therefore, reduce the LED current.
The output current should not exceed the rated current of the LEDs used. The LED current thermal derating should be considered to protect the LEDs. The
maximum voltage of an LED string the demo board
can drive is limited by the duty cycle and the input
voltage of the LT3496. The demo board default
sw itching frequency is 2.1M H z. At this frequency, the
maximum duty cycle is 70% (M IN ). Low er the sw itching frequency results in higher maximum duty cycle.
PERF ORM A NCE SU M M A RY
SYM BO L
PVIN
VIN
VLED
ILED
FSW
η
POUT
PWM D
PAR AM ETER
Pow er Input Supply *
Chip Bias Input Supply **
O utput LED Voltage, per O utput
O utput LED Current, per O utput
Sw itching Frequency
Conversion Efficiency
M aximum Total O utput Pow er
PWM Dimming R atio
The maximum pow er input voltage (PVIN ) is 45V. As a
result, each channel of the demo board can drive up
to ~31V total LED voltage.
Adjustable sw itching frequency allow s optimization of
the efficiency and the external component size. At
2.1M H z, 93% efficiency can be achieved at 500mA
w ith minimum solution size.
Each of the three regulators on the demo board is independently operated. The PWM dimming feature of
the LT3496 allow s True Color PWM dimming w ith the
dimming ratio of 5000:1. Additional analog dimming
is possible.
The LT3476 datasheet gives complete description of
the part, operation and application information. The
datasheet must be read in conjunction w ith this quick
start guide for w orking 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 ofLinear Technology Corporation.
Specifications are at TA = 25°C
CO N DITIO N S
M IN
TYP
3
PVIN = 45V, ILED = 500mA, Fsw =2.1M H z
FADJ=VR EF
ILED = 500mA, PVIN =33V, VIN =3.3V, 10 R ed LEDs
ILED = 500mA
PWM Frequency = 100H z, PVIN =33V, VIN =3.3V, 3
White LEDs at 300mA, 2.1M H z
485
1.9
500
2.1
93
M AX
45
5.5
31
515
2.3
45
U N ITS
V
V
V
mA
M Hz
%
W
5000:1
* 45V is the absolute maximum rating ofthe LT3496. This rating should not be exceeded under any condition.
** VIN of the demo board is limited by the choice of the input capacitor. The LT3496 input range is 3V-30V w ith
transient protection to 40V.
1
LT3496EUFD
Q U ICK STA RT PROCEDU RE
Demonstration circuit 986 is easy to set up to evaluate
the performance of the LT3496EU FD. R efer to
Figure 1 for proper measurement equipment setup
and follow the procedure below :
LED to the LEDn+. Connect the cathode of the last
LED to the LEDn-. All three channels can operate
simultaneously or individually.
5. Turn on PVIN pow er supply.
6. Turn on VIN pow er supply.
1. With pow er off, connect an input pow er supply to
VIN and G N D. To achieve highest efficiency, a low
voltage supply, such as 3.3V or 5V, is recommended.
2. With pow er off, connect a second input pow er supply to PVIN and G N D. The PVIN absolute maximum
rating is 45V.
3. If an output channel n is not used, the PWM n
should be tied to G N D.
4. With pow er off, connect as LED string to an output
channel interested. Connect the anode of the first
2
7. Check for the proper LED current and LED string
voltage.
NOTE. Ifthere is no output, turn offthe pow er supplies. Check all
connections.
8. O nce the proper output current/voltage are established, adjust the parameters w ithin the operating
range and observe the output current regulation, efficiency and other parameters.
9. To observe PWM dimming, turn off all pow er supplies. Connect the PWM n to a pulse generator.
Then repeat step 5 – 8.
LT3496EUFD
Figure 1. Proper M easurem ent Equipm ent Setup
3
LT3496EUFD
4
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