30115003

FIGURE 1. Typical Application Circuit with Fly-Back AC/DC Converter

Overview

The LM3464/64A is a four channel linear current regulator

designed for LED lighting systems with wide input voltage

range, high speed PWM and thermal foldback dimming con-

trol interface. The LM3464/64A incorporates a Dynamic

Headroom Control (DHC) technology which maximizes over-

all efficiency of the lighting system by adjusting the output

voltage of the primary power source dynamically. Linear cur-

rent regulation secures high accuracy output current, LED

and system reliability. High speed PWM dimming provides the

flexibility of brightness control while maintaining constant col-

or temperature of the light. The thermal foldback feature

enables the LM3464/64A to manage the temperature of the

LED heat sink or system chassis with a simple NTC/PTC

temperature sensor. The thermal foldback input can also be

used as an analog dimming control input to adapt to other

sensors easily, such as ambient light sensor.

Dynamic Headroom Control (DHC)

Operation Principles of DHC

Dynamic Headroom Control is a technology that aims at max-

imizing the overall system efficiency by altering the supply

voltage to the LED(s) dynamically in respect to the charac-

teristics of the LED(s). In the LM3464/64A, DHC is facilitated

by connecting a resistor in between the OutP pin of the

LM3464/64A and the voltage feedback node of the primary

power supply (AC/DC) as shown in Figure 2.

30115004

FIGURE 2. Circuitry of the DHC Mechanism

For example, in steady state, when all the output channels

are in regulation and the forward voltage of any LED string

decreases due to temperature raise, the drain voltage of the

corresponding channel (DRx) increases to exceed the default

0.9V typical headroom voltage in order to maintain constant

output current. As the drain voltage increases, the voltage of

CDHC increases and the current sink into the OutP pin de-

creases. This will finally result in decrease of rail voltage

(V

mum level.

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