SC668
Applications Information (continued)
an LED driver bank without any host processor interaction.
Blinking can be initialized via the I 2 C interface at power up
and the settings maintained in the SC668 registers with
no need for additional software interaction.
Two timing parameters must be set to define the blink
effect timing: start time and target time. Start and target
times can be independently set to 32, 64, 256, 512, 1024,
2048, 3072, 4096ms. The total blink cycle time is equal to
the sum of the start and target times.
In addition to timing parameters, start current and target
current values are used to set the bank’s min and max current,
and a combination of bits BxBEN (blink/breathe enable) and
BxFEN (fade enable) are used to enable the blink function.
The four parameters are:
1. Start current — write value to register 02h, 03h, 04h,
or 05h (bank dependent)
2. Target current — write value to register 06, 07h, 08h,
or 09h (bank dependent)
3. Start time — write value to register 10h or 11h (group
dependent)
4. Target time — write to register 10h or 11h (group
dependent)
Figure 4 illustrates the blink effect with respect to time.
For an example of the blink effect, with bank #2 assigned
to group #2, the terms used in the illustration are as
follows:
group #1 and group #2 and can be independently set to
1, 2, 4, 6, 8, 12, or 16ms for each group. The fade function
causes the bank to begin stepping from its current state
to the next programmed state as soon as the new state
is stored in its register. For example, if the bank is set to
25mA, fade is enabled, and the bank is changed to 0mA,
the bank will step from 25mA down to 0mA using all set-
tings between 25mA and 0mA.
In addition to the 32 programmable backlight current
values, there are also 75 non-programmable current steps.
The non-programmable steps are active only during a fade
or breathe operation to provide for a very smooth change
in backlight brightness. Backlight current steps proceed at
a programmable fade rate of 1, 2, 4, 6, 8, 12, or 16ms. The
exact length of time used to fade between any two back-
light values is determined by multiplying the fade rate by
the number of steps between the old and new backlight
values. The fade time can be calculated from the data pro-
vided in Table 1 on page 19.
Two parameters must be programmed to enable the fade
effects: effect rate and start current. The fade function will
begin when a new start current is set along with the FEN
bit in the associated register.
The fade effect rate parameter must be set to define the
fade timing. Group #1 and group #2 have independent
sets of timing parameters to support a variety of fade
timing options. When a bank is assigned to a group, it
adopts the timing parameters of the respective group.
?
?
?
?
I BL_START = contents of register 03h (B2FEN must
equal 0)
I BL_TARGET = contents of register 07h (B2BEN must
equal 1)
t START = contents of bits ST2_[2:0] in register 11h
t TARGET = contents of bits TT2_[2:0] in register 11h
Registers associated with fade are described below:
1. Effect Rate — write a value to register 0Fh (group
dependent)
2. Start Current — write value to register 02h, 03h, 04h,
or 05h (bank dependent)
Backlight Fade-In and Fade-Out Lighting Effects
When enabled, the fade function causes the backlights to
change brightness by stepping the current incrementally
until the final backlight current is reached. The backlight
fade-in and fade-out may be applied to selected banks.
When enabled, the bank current will gradually increase
during fade-in and gradually decrease during fade-out.
The rate of increase or decrease is programmable for
Figure 5 illustrates the fade-in and fade-out effects with
respect to time. For an example of the fade effects assigned
to bank 3 with effect rate 2, the terms in the illustration are
as follows:
? I BL_INITIAL = contents of register 04h (B3FEN must
equal 1)
15
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