SC643 datasheet(24/26 Pages) SEMTECH

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SC643

SFADE1 and SFADE0 [D5:D4]

These bits are used to set the rise/fall rate between two

backlight currents for the sub display as show in Table 11.

For the fade feature to be active, the SFADE bit must be

set. The number of steps required to change the backlight

current will be equal to the change in binary count of bits

SBL4 through SBL0.

Table 11 — Sub Display Fade Control Bits

SFADE1

SFADE0

Fade Feature Rise/

Fall Rate (ms/step)

SFADE [D3]

This bit is used to enable or disable the fade feature. When

SFADE is enabled and a new main backlight current is set,

the current will change from its existing setting to the new

setting written in SBL[4:0] at the rate determined by

SFADE1 and SFADE0 (in ms/step). A new setting cannot

be written during an ongoing fade operation, but an on-

going fade operation may be cancelled by writing 0 to the

SFADE bit. Clearing the SFADE bit during an ongoing fade

operation changes the current immediately to the value

of SBL[4:0]. The number of counts to complete a fade

operation equals the difference between the old and new

SBL[4:0] settings. If SFADE is cleared, the current level will

change immediately without the fade delay. The rate of

fade may be changed dynamically by writing new values

to the SFADE1 and SFADE0 bits. The total fade time is

given by the number of steps between old and new back-

light values (see Table 5), multiplied by the rate of fade in

ms/step.

Bank Selection Register (0Ah)

This register contains the bits that determine which LED

drivers are assigned to the main display and which are

part of the sub display bank.

Bits [D5:D3]

These bits are unused and are always zeroes.

MB2, MB1, and MB0 [D2:D0]

These bits are used to set the number of LED drivers dedi-

cated to a main backlight function. This allows the device

to drive two different sets of LEDs with different settings

for use in products like clamshell-style mobile phones that

have a main display and a sub display with different light-

ing requirements. Note that any driver not selected for

the main display will automatically be assigned to the sub

display set. The code set by these three bits determines

which LED drivers are dedicated to the main display

according to the assignments listed in Table 12.

Table 12 — Main Display Driver Assignment Codes

MB2

MB1

MB0

Main Display

LED Drivers

Sub Display

LED Drivers

BL1 - BL5

none

BL1 - BL4

BL5

BL1 - BL3

BL4 - BL5

BL1 - BL2

BL3 - BL5

BL1

BL2 - BL5

000 and 110 through 111

BL1 - BL5

(default)

none

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