LM3463_12 Datasheet, PDF (28/40 Pages) Texas Instruments – LM3463 Dynamic Headroom Controller with Thermal Control Interface and Individual Channel Dimming Control

LM3463
SNVS807 – MAY 2012
www.ti.com
In DC interface mode, the DIM01, DIM23, DIM4 and DIM5 pins accept DC voltages in the range of 0.8V to 5.7V
to facilitate PWM dimming control. The voltage at the DIMn pins (V_DIMn) and the PWM dimming duty in the DC
interface mode (D_DC-DIM) are governed by the following equation. Figure 17 shows the correlation of V_DIMn and
D_DC-DIM. The conversion characteristic is shown in Figure 18.
(14)
where 0.8V < V_DIMn < 5.7V
The PWM dimming frequency in the DC interface mode is defined by the system clock of the LM3463. The
dimming frequency in the DC interface mode is equal to the system clock frequency divided by 1280 which
follows the equation below:
(15)
In order to achieve a 256 level (8–bit resolution) brightness control, the minimum on time of every channel
(1/(f_SERIAL-DIM*256)) should be no shorter than 8 us, thus a dimming frequency of 488Hz is suggested to use.
The LM3463 samples the analog voltage at the DIMn pins and updates the dimming duty of each output channel
at a rate of 1280 system clock cycle (1280/f_CLKOUT). In order to ensure correct conversion of analog voltage to
PWM dimming duty, the slew rate of the analog voltage for dimming control is limited the following equation:
(16)
100
80
60
40
20
0
01234567
VDIMn(V)
Figure 17. Dimming Duty vs V_DIMn in DC interface mode
28
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