LM3530 datasheet(14/50 Pages) TI1

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Zone 0

Zone 1

Zone 2

Zone 3

Zone 4

µ5¶= Rest, µ+¶= Increase, µ-µ= Decrease

Brightness

Zone

Zone 0

Zone 1

Zone 2

Zone 3

Zone 4

Brightness

Zone

Zone 0

Zone 1

Zone 2

Zone 3

Zone 4

Brightness

Zone

Averager Output

Zone 0

Zone 1

Zone 2

Zone 3

Zone 4

Averager

Output

Zone

Average

1.0

1.75

3.5

4.0

2.25

1.5

LM3530

SNVS606L – JUNE 2009 – REVISED DECEMBER 2014

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Feature Description (continued)

2. The Averager will always round down to the lower zone in the event of a non-integer zone average. For

example, if during an averaging period the ALS input transitions between zones 1 and 2 resulting in an

averager output of 1.75, then the averager output will round down to 1 (see Figure 28).

3. The two most current averaging samples are used to make zone change decisions.

4. To make a zone change, data from three averaging cycles are needed. (Starting Value, First Transition,

Second Transition or Rest).

5. To Increase the brightness zone, the Averager output must have increased for at least 2 averaging periods

or increased and remained at the new level for at least two averaging periods ('+' to '+' or '+' to 'Rest' in

Figure 29).

6. To decrease the brightness zone, the Averager output must have decreased for at least 2 averaging periods

or decreased and remained at the new level for at least two averaging periods ('-' to '-' or '-' to 'Rest' in

Figure 29).

In the case of two consecutive increases or decreases in the Averager output, the LM3530 will transition to zone

equal to the last averager output (Figure 29).

Using the diagram for the ALS block (Figure 26), the flow of information is shown in (Figure 30). This starts with

the ALS input into the A/D, into the Averager, and then into the Discriminator. Each state filters the previous

output to help prevent unwanted zone to zone transitions.

When using the ALS averaging function, it is important to remember that the averaging cycle is free running and

is not synchronized with changing ambient lighting conditions. Due to the nature of the averager round down, an

increase in brightness can take between 2 and 3 averaging cycles to change zones, while a decrease in

brightness can take between 1 and 2 averaging cycles. See Table 6 for a list of possible Averager periods.

Figure 31 shows an example of how the perceived brightness change time can vary.

Figure 28. Averager Calculation

Figure 29. Brightness Zone Change Examples

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