LM3464, LM3464A

SNVS652F – APRIL 2010 – REVISED MAY 2013

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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 control interface. The LM3464/64A incorporates a

Dynamic Headroom Control (DHC) technology which maximizes overall efficiency of the lighting system by

adjusting the output voltage of the primary power source dynamically. Linear current regulation secures high

accuracy output current, LED and system reliability. High speed PWM dimming provides the flexibility of

brightness control while maintaining constant color 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 maximizing the overall system efficiency by altering the

supply voltage to the LED(s) dynamically in respect to the characteristics 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 15.

Figure 15. 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 decreases. This will

finally result in decrease of rail voltage (VRAIL) until the corresponding DRx voltage returns to minimum level.

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