c644ultrt Semtech Corporation, c644ultrt Datasheet - Page 13

• Manufacturer Part Number: c644ultrt
• Description: Light Management Unit With 4 Ldos And Sempulse Interface
• Manufacturer: Semtech Corporation

Applications Information (continued)
Main and Sub Backlight Bank Configuration
The six LED backlight drivers can be configured as a single
bank or as two independent banks — one dedicated for
a main display and the other for a sub display. This feature
allows the device to drive two sets of LEDs with different
settings so different current and fade settings can be
used.
The Register Map contains two separate control registers
for main and sub currents. Register 0h contains the
current setting code for the main bank, and register 02h
contains the setting code for the sub bank. There are also
three bits in register 0Ah that control which drivers are
assigned to each display. The default setting assigns all
six LED drivers to the main display control register. In this
scenario, the current control settings for each LED driver
come from register 0h. Other settings are available that
allow the groupings to be defined so that any number
from  to 6 drivers can be grouped as the main display
backlight drivers, with the remaining drivers assigned to
the sub display backlight by default. See Table 8 of the
Register Map section for more details.
Backlight Fade-in and Fade-out Function
Register 09h contains bits that control the fade state of
each display (main and sub). When enabled, the fade
function causes the backlight settings to step from their
current state to the next programmed state as soon as
the new state is stored in its register. For example, if the
backlight is set at 25mA and the next setting is the off
state, the backlight will step from 25mA down to 0mA
using all 29 settings at the fade rate specified by the bits
in register 09h. The same is true when turning on or
increasing the backlight current — the backlight current
will step from the present level to the new level at the
step rate defined in register 09h. This process applies for
both the main and the sub displays. The state diagram in
Figure  describes all possible conditions for a fade opera-
tion. More details can be found in the Register Map
section.
Fade-In from Off State
When the initial state of the main or sub backlight current
register is 00h (the data value for 0mA), fading to an on
state is accomplished by following the steps listed in
Table . Following these steps explicitly will ensure that
the fade-in operation will proceed with no interruption at
the rate specified in the Main/Sub Backlight Fade register
(09h). This procedure must be followed regardless of
which backlight grouping configuration is being used.
Note that it is only necessary to set the BLEN bits for the
main or sub display that is required to fade.
Figure 1 — State Diagram for Fade Function
Fa�e=0
new bright
Imme�iate
change to
Write FADE=0
le�el
No change
change
No
Fa�e=1
Write
Fa�e
en��
fa�e u�ing
FADE=0
Continue
new rate
FADE=0
Write
proce��ing
FADE=0
FADE=1
Fa�e
FADE=1
FADE=1
new fa�e
Write new
Write
Write
bright
rate
le�el
begin�
(1�
Fa�e
change
Note:
(1� When the �ata in backlight
enable regi�ter 00h i� not 00h
change to new
FADE=1
bright le�el
�alue from current
Fa�e i� re�irecte�
bright le�el
Write new
Write new
bright le�el
No
Write
Imme�iate
towar� the new
�tate
SC644
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