2

dc2176af

DEMO MANUAL DC2176A

Quick start proceDure

ToevaluatetheperformanceoftheLT3909usingDC2176A,

refer to Figure 1 for the proper measurement equipment

setup and then follow the procedure below:

NOTE: An external voltage must be applied to the PWM

terminal in order for DC2176A to operate. See Step 4 for

details.

1. Connect two strings of LEDs with a forward voltage of

35V or less and corresponding meters.

2. Connect the EN/UVLO terminal to GND with a clip-on

lead.

3. With the power off, connect the input power supply and

corresponding meters.

4. Apply an external voltage to the PWM terminal. The

external voltage can be a 2V to 5V DC source or a 100Hz

or higher PWM dimming signal. Install resistor R10 to

is not desired.

lowed to exceed the LED voltage by a few volts, but

activate overtemperature protection or dissipate too

much power in the LT3909.

6. Release the EN/UVLO to GND connection.

7. Once the LED strings are running at the programmed

LED current; adjust the input voltage within the operat-

ing range and observe the LED current regulation or

reduction in brightness with LED dimming.

PARAMETERS

CONDITIONS

MIN

TYP

MAX

UNITS

7

V

36

V

R2 = 976k 1%, R3 = 31.6k 1%

35

V

40

mA

5.9

V

5

V

Efficiency

86

%

Switching Frequency

2

MHz