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.