LM3463 datasheet(13/43 Pages) TI2

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DHC Circuit

VREF

Regulator

VCC

LM3463

DRn

GDn

SEn

GND

IOUTADJ

VREF

REFRTN

RIADJ1

RIADJ2

RISNSn

To LED

Cathode

LM3463

www.ti.com

SNVS807A – MAY 2012 – REVISED MAY 2013

Overview

The LM3463 is a six channel linear current regulator which designed for LED lighting applications. The use of the

Dynamic Headroom Control (DHC) method secures high system power efficiency and prolongs system operation

lifetime by minimizing the power stress on critical components. The output currents of the LM3463 driver stage

are regulated by six individual low-side current regulators.

The current regulators are accompanied by a high precision current sensing circuit. In order to ensure excellent

current matching among output channels, the current sensing inputs are corresponding to a dedicated reference

point, the REFRTN pin to insulate the ground potential differences due to trace resistances. With this current

sensing circuit, the channel to channel output current difference is well controlled below ±10% when the output

current is reduced (DC LED current reduction) to 5%.

LED Current Regulators and Analog Dimming Control

The LM3463 provides six individual linear current regulators to perform LED current regulation. Each current

regulator includes an internal MOSFET driver and error amplifier and an external MOSFET and current sensing

resistor. The output current of every output channel is defined by the value of an external current sensing resistor

individually. The reference voltage of the regulators can be adjusted by changing the bias voltage at the

IOUTADJ pin.

When analog dimming control applies, the output current of all channels reduces proportional to the voltage

being applied to the IOUTADJ pin. Figure 18 shows the simplified block diagram of a current regulator.

Figure 18. Block diagram of a linear current regulator

Since the driving current of a LED string is determined by the resistance of the current sensing resistor RISNSn

individually, every channel can have different output current by using different value of RISNSn. The LED current,

IOUTn is calculated using the following expression:

(1)

AND since:

(2)

Thus,

(3)

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