1FEATURES

? Integrated Phase Angle Decode

– Leading and Trailing Edge Compatible

– Over 50:1 Dimming Range

? Power Factor Correction with Low Total

Harmonic Distortion

? Primary Side Control Using Input Voltage

Feedforward Technique

? Input Power Regulation Scheme with Improved

Line Regulation

? Constant Power Operation of LEDs to

Compensate for Forward Voltage Variations

Over Temperature and Lifetime

? Fixed Frequency Discontinuous Conduction

Mode Operation

? Valley Switching Operation to Achieve High

Efficiency and Low EMI

? Efficient TRIAC Hold Current Management

? Thermal Foldback Function for LED Protection

? LED Open Circuit and Short Circuit Protection

APPLICATIONS

? Dimmable A19, R20, PAR30/38 LED Lamps

? Recessed LED Downlights and Pendant Lights

? Industrial and Commercial Solid State Lighting

DESCRIPTION

The LM3447 is a versatile power factor correction

(PFC) controller designed to meet the performance

requirements of residential and commercial phase-cut

dimmer compatible LED lamp drivers. The device

incorporates a phase decoder circuit and an

adjustable hold current circuit to provide smooth,

flicker free dimming operation. A proprietary primary

side control technique based on input voltage

feedforward is used to regulate the input power

drawn by the LED driver and to achieve line

regulation over a wide range of input voltage. Valley

switching operation is implemented to minimize

switching loss and reduce EMI. An internal thermal foldback circuit is provided to protects the LEDs from

damage based on the temperature sensed by a

single external NTC resistor. Additional features

include LED open circuit and short circuit protection,

cycle-by-cycle FET over-current protection, burst

mode fault operation using an internal 812ms fault

timer and internal thermal shutdown.

The LM3447 is ideal for implementing dimmable,

isolated single stage LED lamp drivers where

simplicity, low-component count and small solution

size are of primary importance. This device is

currently available in a TSSOP 14-pin package.