1 Features

1• TRIAC Dim Decoder Circuit for LED Dimming

• Application Voltage Range 80 V AC to 277 VAC

• Capable of Controlling LED Currents Greater

Than 1 A

• Adjustable Switching Frequency

• Low Quiescent Current

• Adaptive Programmable Off-Time Allows for

Constant Ripple Current

• Thermal Shutdown

• No 120-Hz Flicker

• Low Profile 10-Pin VSSOP Package or 14-Pin

SOIC

• Patented Drive Architecture

2 Applications

• Retro Fit TRIAC Dimming

• Solid State Lighting

• Industrial and Commercial Lighting

• Residential Lighting

3 Description

The LM3445 is an adaptive constant off-time AC/DC

buck (step-down) constant current controller designed

to be compatible with TRIAC dimmers. The LM3445

provides a constant current for illuminating high

power LEDs and includes a TRIAC dim decoder. The

dim decoder allows wide range LED dimming using

standard TRIAC dimmers. The high frequency capable architecture allows the use of small external

passive components. The LM3445 includes a bleeder

circuit to ensure proper TRIAC operation by allowing

current flow while the line voltage is low to enable

proper firing of the TRIAC. A passive PFC circuit ensures good power factor by drawing current directly

from the line for most of the cycle, and provides a

constant positive voltage to the buck regulator.

Additional features include thermal shutdown, current

limit and VCC under-voltage lockout.