SC668 datasheet(15/46 Pages) SEMTECH

15 / 46 page

SC668

Applications Information (continued)

an LED driver bank without any host processor interaction.

Blinking can be initialized via the I2C 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:

Start current — write value to register 02h, 03h, 04h,

or 05h (bank dependent)

Target current — write value to register 06, 07h, 08h,

or 09h (bank dependent)

Start time — write value to register 10h or 11h (group

dependent)

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:

BL_START = contents of register 03h (B2FEN must

equal 0)

BL_TARGET = contents of register 07h (B2BEN must

equal 1)

START = contents of bits ST2_[2:0] in register 11h

TARGET = contents of bits TT2_[2:0] in register 11h

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

•

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.

Registers associated with fade are described below:

Effect Rate — write a value to register 0Fh (group

dependent)

Start Current — write value to register 02h, 03h, 04h,

or 05h (bank dependent)

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:

BL_INITIAL = contents of register 04h (B3FEN must

equal 1)

•

SC668 Datasheet(PDF) 15 Page - Semtech Corporation

SC668 Datasheet(HTML) 15 Page - Semtech Corporation

Html Pages

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46

Datasheet Download

Link URL