SC668 datasheet(16/46 Pages) SEMTECH

16 / 46 page

SC668

Applications Information (continued)

BL_FINAL = new value written to register 04h (register

07h bit B3BEN must equal 0), however, the“Target”

value of register 07h has no effect on fade.

FADE_IN = contents of bits ER2_[2:0] in register 0Fh

FADE_OUT = tFADE_IN

Auto-Dim Lighting Effect

Two auto-dim settings are provided — auto-dim full and

auto-dim partial. These settings provide automatic

dimming of bank #1.The auto-dim delay times are set using

the group #1 target and start time register (10h). Delay

times are 8 times the group #1 target and start times.

Auto-dim full provides a time-out and dimming function

followed by a time-out and turn-off function. Auto-dim

full begins when the bank is enabled (or re-enabled), the

bank will first go to the target current and wait for a count

of 8 times the group #1 target time. The bank will then

dim to the “start” current and wait for a count of 8 times

the group #1 start time. The bank will then turn off.

Auto dim partial provides the time-out and dimming func-

tion, but does not turn off backlights. Auto-dim partial

begins when the bank is enabled (or re-enabled), the bank

will first go to the target current and wait for a count of 8

times the group #1 target time. The bank will then dim to

the“start”current. The bank will not turn off automatically.

Auto-dim is available only for group #1. After selecting an

auto-dim option, the bank’s blink effect must be enabled to

enable auto-dim. The bank must then be enabled or re-

enabled to begin the auto-dim. Auto-dim partial is illustrated

in Figure 6, and auto-dim full is illustrated in Figure 7.

Brightness Change without Effects

There are two ways to change brightness while using no

lighting effect. One way is to set the effect rate option to

the zero value “snap to target”(a function of register 0Fh).

This method will block all lighting effects on all banks

within a group. Another way to change brightness, with

no lighting effect, is to set the BxFEN and BxBEN both

equal to zero. This second method will block all lighting

effects on a single bank, and with no influence over other

banks within the group.

Writing a new value to the backlight current register, while

effects are disabled, will cause the change in brightness to

•

occur immediately. When changing brightness without

effects, registers 02h through 05h are used for this func-

tion. The target values of registers 06h through 09h are

not involved.

Figure 8 illustrates the brightness change with respect to

time. An example of brightness change to bank #4 with

no lighting effect, is as follows:

BL_INITIAL = previous value written to register 05h

BL_FINAL = new value written to register 05h

The register 05h bit B4FEN must equal 0, and register 09h

bit B4BEN must equal 0, however, the “Target” value of

Fade State Diagram

The state diagram in Figure 2 describes the fade opera-

tion. If the backlight enable bits are disabled during an

Write

BxFEN=0

Write new

bright level

No change

Write new

bright

level

Write new

bright level

Fade is

redirected toward

the new value

from current

state

Fade

begins

Fade

ends

Immediate

change to

new bright

level

change

No change

Immediate

change to new

bright level

Write

new fade

rate

Continue

fade using

new rate

Write entire

bank’s enable bits

BLxEN = 0

Bank

turns off

immediately

Write

BLxEN = 1

Fade begins

at 0mA

Fade

processing

BxFEN=0

Backlights

disabled

Write

BxFEN=1

Write

BxFEN=0

BxFEN=1

Write

BxFEN=1

Write

BxFEN=0

Write {0,0,0}

to effect rate

bits register

0Fh

Write

BxFEN=1

Figure 2 — State Diagram for Fade Function

•

SC668 Datasheet(PDF) 16 Page - Semtech Corporation

SC668 Datasheet(HTML) 16 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