SC667 datasheet(42/47 Pages) SEMTECH

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SC667

The ALS comparator functions are shown in Table 23.

Table 23 — ALS Comparator Function(1)

Conditions

OUT Effect on Bank #1

OUT > ADRISE

Brightness changes to target value

OUT < ADFALL

Brightness changes to start value

FALL ≤ ADOUT ≤ ADRISE

Brightness does not change

FALL ≥ ADRISE

Hysteresis between the rising and falling

thresholds is disabled and . . .

FALL → has no effect on brightness

O > ADRISE → brightness changes to

target value

O < ADRISE → brightness changes to

start value

O = ADRISE → brightness does not change

Note:

1) When AD_AUTO bit is high.

The state diagram of Figure 29 shows how the ADC is used

to change the brightness of backlight bank #1. No auto-

matic change in brightness occurs when AD_AUTO = 0.

ADOUT > ADRISE

ADOUT < ADFALL

ADOUT < ADRISE

AD_AUTO = 1 or 0

AD_AUTO = 1

AD_AUTO = 0

ADOUT > ADRISE

Bank #1 Brightness

= Value of Register 02h

ADOUT > ADFALL

AD_AUTO = 1 or 0

Bank #1 Brightness

= Value of Register 06h

ADOUT < ADFALL

Figure 29 — ADC function at Bank #1 Brightness

ADC Output and Threshold Register (13h)

This register contains the value AD

OUT which is compared

with AD

RISE and ADFALL. The contents of ADOUT may originate

automatically from the ADC, when the AD_EN bit is a logic

one. Alternatively, AD

OUT may be written to the register via

the I2C interface when the AD_EN bit is a logic zero.

When AD_EN = 1, the ADC receives its analog voltage

input signal from the external photo-detector circuit con-

nected to the ADI pin. V

ADI is then converted into digital

and stored as the 8 bit word AD

OUT. The reference voltage

for the ADC is provided internally by the output of LDO4

LDO4). When the voltage VADI is equal to VLDO4 , the ADC is

at full-scale value FFh, and AD

OUT will equal FFh.

When using an external photo-detection circuit, the ADC

requires the LDO output voltage V

LDO4 to remain constant.

LDO4 can drop-out if the supply voltage becomes too low.

LDO4 should be set to a value sufficiently low to guard

against drop-out.

To prevent drop-out, the maximum LDO4 output setting

should be limited to: V

LDO4(MAX) = VIN(MIN) - [1.33 × ILDO4(MAX)],

where V

IN(MIN) is the minimum battery voltage and ILDO4(MAX)

is the maximum load current of LDO4. LDO4 load current

includes current to the external photo-detection circuit.

AD_O7 through AD_O0 [D7:D0]

These are the 8 bits of AD

OUT. AD_O7 [D7] is the Most

Significant Bit (MSB), and AD_O0 [D0] is the Least

Significant Bit (LSB). Binary weights of these bits are

shown in Table 24.

Table 24 — AD

OUT Bits [D7:D0]

Name

Bit

Binary Weight

AD_O7

1/2

AD_O6

1/4

AD_O5

1/8

AD_O4

1/16

AD_O3

1/32

AD_O2

1/64

AD_O1

1/128

AD_O0

1/256

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