Datasheet
VCC
Regulator
LM3463
GND
47 k
VCC
BUF
GND
DIMnO/P
GND
External PWM
signal source
(e.g. MCU)
BUF
To dimming
control
circuit
PWM
signal
R
PU
Open-drain output
2 M
LM3463
SNVS807A –MAY 2012–REVISED MAY 2013
www.ti.com
Dimming Mode Control
The LM3463 provides three modes of PWM dimming control. The three modes are: Direct PWM dimming mode,
Serial interface mode and DC interface mode. Selection of the mode of dimming mode is made by leaving the
MODE pin open or connecting the MODE pin to GND or VCC. Regardless of the selection of the mode of PWM
dimming control, the output channels 0 and 1 are controlled commonly by the signal at the DIM01 pin and the
output channels 2 and 3 are controlled commonly by the PWM signal at the DIM23 pin. The dimming duty of the
channel 4 and 5 are controlled by the signals on DIM4 and DIM5 pins respectively.
The DIM01, DIM23, DIM4 and DIM5 pins are pulled down by an internal 2 MΩ weak pull-downs to prevent the
pins from floating. Thus the dimming control input pins are default to 'LED OFF' state and need external pulled
up resistors when the pins are connected to open collector/drain signal sources. Figure 30 shows a suggested
circuit for connecting the LM3463 to an open collector/drain dimming signal sources.
Figure 30. Adding an external pull-up resistor to the DIMn pin
Direct PWM Dimming Mode
Connecting the MODE pin to ground enables direct PWM dimming mode. Every dimming control pin (DIM01 to
DIM5) in direct PWM control mode accepts active high TTL logic level signal. In direct PWM dimming mode, the
six output channels are separated into four individual groups to accept external PWM dimming signals. The
configuration of output channels are as listed in the following table:
Group A CH0 and CH1, controlled by DIM01 pin
Group B CH2 and CH3, controlled by DIM23 pin
Group C CH4, controlled by DIM4 pin
Group D CH5, controlled by DIM5 pin
In order to secure accurate current regulation, the pull-up time of every dimming control input must not be shorter
than 8 µs. If a 256 level (8-bit resolution) brightness control is needed, the PWM dimming frequency should be
no higher than 488Hz.
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