SC653 datasheet(13/22 Pages) SEMTECH

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SC653

Applications Information (continued)

Backlight Quiescent Current

The quiescent current required to operate all four back-

lights is reduced by 1.5mA when backlight current is set

to 4.0mA or less. This feature results in higher efficiency

under light-load conditions. Fur ther reduction

in quiescent current will result from using fewer than four

LEDs.

Fade-In and Fade-Out

The SC653 contains bits that control the fade state of the

main bank. 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 04h. 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 04h. This

process applies for both the main and the sub displays.

The fade rate may be changed dynamically when a fade

operation is active by writing new values to the fade reg-

ister. When a new backlight level is written during an

ongoing fade operation, the fade will be redirected to the

new value from the present state. An ongoing fade opera-

tion may be cancelled by disabling fade which will result

in the backlight current changing immediately to the final

value. If fade is disabled, the current level will change

immediately without the fade delay. The state diagram in

Figure 1 describes all possible conditions for a fade opera-

tion. More details can be found in the Register Map

Section.

Write FADE=0

Write new

bright level

FADE=0

No change

Write

FADE=0

FADE=1

Fade

processing(1)

Write new

bright

level

Write new

bright level

Fade is redirected

toward the new

value from current

state

Fade

begins

Fade

ends

Write

FADE=1

FADE=0

Immediate

change to

new bright

level

Fade=0

Write

Fade=1

change

Write

FADE=1

change

Immediate

change to new

bright level

Write

new fade

rate

Continue

fade using

new rate

Note:

(1) When the data in backlight

enable register 01h is not 00h

Figure 1 — Fade State Diagram

Programmable LDO Outputs

Two low dropout (LDO) regulators are provided for

camera module I/O and core power. Each LDO output

voltage setting has ±3.5% accuracy over the operating

temperature range. Output current greater than the

specification is possible at somewhat reduced accuracy.

Input pins ENL1 and ENL2 may be used to directly enable

and disable the LDOs without communication via the

SPIF interface. When power is first applied to the SC653,

the register defaults reset the LDOs to the off state, so

SPIF must be used one time to set the voltages before

ENL1 and ENL2 can be used to enable the LDOs.

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