LM3463_12 Datasheet, PDF (14/40 Pages) Texas Instruments – LM3463 Dynamic Headroom Controller with Thermal Control Interface and Individual Channel Dimming Control

LM3463
SNVS807 – MAY 2012
www.ti.com
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 1 shows the simplified block diagram of a current regulator.
VREF
RIADJ1
IOUTADJ
VCC
VREF
Regulator
LM3463
DHC Circuit
To LED
Cathode
DRn
GDn
RIADJ2
SEn
RISNSn
REFRTN
GND
Figure 1. 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 R_ISNSn
individually, every channel can have different output current by using different value of R_ISNSn. The LED current,
I_OUTn is calculated using the following expression:
(1)
AND since:
Thus,
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(2)
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