LM3532 datasheet(20/52 Pages) TI2

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LM3532

SNVS653E – JULY 2011 – REVISED AUGUST 2015

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For each algorithm, the ALS follows these basic rules:

ALS Rules

1. For the ALS Interface to force a change in the backlight current (to a higher zone target), the averager output

must have shown an increase for 3 consecutive average periods, or an increase and a remain at the new

zone for 3 consecutive average periods.

2. For the ALS Interface to force a change in the backlight current (to a lower zone target), the averager output

must have shown a decrease for 3 consecutive average periods, or a decrease and remain at the new zone

for 3 consecutive average periods.

3. If condition 1 or condition 2 is satisfied, and during the next average period, the averager output changes

again in the same direction as the last change, the LED current immediately changes at the beginning of the

next average period.

4. If condition 1 or condition 2 is satisfied and the next average period shows no change in the average zone,

or shows a change in the opposite direction, then the criteria in step 1 or step 2 must be satisfied again

before the ALS interface can force a change in the backlight current.

5. The Averager Output (see Figure 16) contains the zone that is determined from the most recent full average

period.

6. The ALS Interface only forces a change in the backlight current at the beginning of an average period.

7. When the ALS forces a change in the backlight current the change is to the brightness target pointed to by

the zone in the Averager Output.

7.4.10.12 Direct ALS Control

In direct ALS control the LM3532’s ALS Interface can force the backlight current to either a higher zone target or

a lower zone target using the rules described in the ALS Rules Section.

Figure 19 shows the ALS voltage, the current average zone which is the zone determined by averaging the ALS

voltage in the current average period, the Averager Output which is the zone determined from the previous full

average period, and the target backlight current that is controlled by the ALS Interface. The following steps detail

the Direct ALS algorithm:

1. When the ALS is enabled the ALS fast start-up (1.1ms average period) quickly brings the Averager Output to

the correct zone. This takes 3 fast average periods or approximately 3.3 ms.

2. The 1st average period the ALS voltage averages to Zone 4.

3. The 2nd average period the ALS voltage averages to Zone 3.

4. The 3rd average period the ALS voltage averages to Zone 3 and the Averager Output shows a change from

Zone 4 to Zone 3.

5. The 4th average period the ALS voltage averages to Zone 2 and the Averager Output remains at its changed

state of Zone 3.

6. The 5th average period the ALS voltage averages to Zone 1. The Averager Output shows a change from

Zone 3 to Zone 2. Because this is the 3rd average period that the Averager Output has shown a change in

the decreasing direction from the initial Zone 4, the backlight current is forced to change to the current

Averager Output (Zone 2's) target current.

7. The 6th average period the ALS voltage averages to Zone 2. The Averager Output changes from Zone 2 to

Zone 1. Because this is in the same direction as the previous change, the backlight current is forced to

change to the current Averager Output (Zone 1's) target current.

8. The 7th average period the ALS voltage averages to Zone 3. The Averager Output changes from Zone 1 to

Zone 2. Because this change is in the opposite direction from the previous change, the backlight current

remains at Zone 1's target.

9. The 8th average period the ALS voltage averages to Zone 3. The Averager Output changes from Zone 2 to

Zone 3.

10. The 9th average period the ALS voltage averages to Zone 3. The Averager Output remains at Zone 3.

Because this is the 3rd average period that the Averager Output has shown a change in the increasing

direction from the initial Zone 1, the backlight current is forced to change to the current Averager Output

(Zone 3's) target current.

11. The 10th average period the ALS voltage averages to Zone 4. The Averager Output remains at Zone 3.

12. The 11th average period the ALS voltage averages to Zone 4. The Averager Output changes to Zone 4.

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