SC643 datasheet(23/26 Pages) SEMTECH

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SC643

LDO4 Control Register (08h)

This register is used to enable LDO4 and set its output

voltage level. The ENL4 pin must be high for register 08h

to control LDO4. ENL4 has a logical AND function with the

LDO4

=0V

regardless of the contents of register 08h.

Bits [D5:D4]

These bits are unused and are always zeroes.

LDO4V3 through LDO4V0 [D3:D0]

These bits are used to set the output voltage of LDO4 as

shown in Table 9.

Table 9 — LDO4 Control Codes

LDO4V3

LDO4V2

LDO4V1

LDO4V0

LDO4

0000

OFF

0001

3.3V

0010

3.2V

0011

3.1V

0100

3.0V

0101

2.9V

0110

2.8V

0111

2.7V

1000

2.6V

1001

2.5V

1010

2.4V

1011

2.2V

1100

1.8V

1101

1.7V

1110

1.6V

1111

1.5V

Fade Control Register (09h)

This register contains the fade enables and rate controls

for both the main display and sub display LED driver

banks.

MFADE1 and MFADE0 [D2:D1]

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

backlight currents for the main display as show in Table

10. For the fade feature to be active, the MFADE bit must

be set. The number of steps required to change the back-

light current will be equal to the change in binary count

of bits MBL4 through MBL0.

Table 10 — Main Display Fade Control Bits

MFADE1

MFADE0

Fade Feature Rise/

Fall Rate (ms/step)

MFADE [D0]

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

When MFADE is enabled and a new main backlight

current is set, this current will change from its existing

value to the new value written in MBL[4:0] at the rate

determined by MFADE1 and MFADE0 (in ms/step). A new

setting cannot be written during an ongoing fade opera-

tion, but an on-going fade operation may be cancelled by

writing 0 to the MFADE bit. Clearing the MFADE bit during

an ongoing fade operation changes the current immedi-

ately to the value of MBL[4:0]. The number of counts to

complete a fade operation equals the difference between

the old and new MBL[4:0] settings. If MFADE 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 MFADE1 and MFADE0 bits.

The total fade time is given by the number of steps

between old and new backlight values (see Table 4), mul-

tiplied by the rate of fade in ms/step.

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