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.