LM3533 Datasheet, PDF (24/53 Pages) Texas Instruments – Complete Lighting Power Solution for Smartphone Handsets

LM3533
ALS ALGORITHMS
There are three ALS algorithms that can be selected independently by each ALS Mapper (ALSM1, ALSM2, and ALSM3) (see
Table 23 ). The ALS algorithms are: direct, up only, and down delay.
ALS RULES
For each algorithm, the ALS follows these basic 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 #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 will immediately change at the beginning of the next average period.
4. If condition #1 or #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 #2 must be satisfied again before the ALS interface can force a change in the
backlight current.
5. The Averager Output (see Figure 8) 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 will be to the brightness target pointed to by the zone in
the Averager Output.
DIRECT ALS CONTROL
In direct ALS control the LM3533’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. In the example of Figure 11, the plot 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 startup (1.1ms average period) quickly brings the Averager Output to the correct zone.
This takes 3 fast average periods or approximately 3.3ms.
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 0 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.
Since 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. Since 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. Since 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. Since 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.
13. The 12th average period the ALS voltage averages to Zone 4. The Averager Output remains at Zone 4.
14. The 13th average period the ALS voltage averages to Zone 4. The Averager Output remains at Zone 4. Since this is the 3rd
average period that the Averager Output has shown a change in the increasing direction from the initial Zone 3, the backlight
current is forced to change to the current Averager Output (Zone 4's) target current.
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