LM3533 Datasheet, PDF (25/53 Pages) Texas Instruments – Complete Lighting Power Solution for Smartphone Handsets

LM3533
FIGURE 11. Direct ALS Control
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UP-ONLY CONTROL
The ALS Up-Only Control algorithm is similar to Direct ALS Control except the ALS Interface can only program the backlight current
to a higher zone target. Referring to Figure 12:
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 1.
3. The 2nd average period the ALS voltage averages to Zone 0.
4. The 3rd average period the ALS voltage averages to Zone 0, and the Averager Output shows a change from Zone 1 to Zone
0.
5. The 4th average period the ALS voltage averages to Zone 2, and the Averager Output remains at its changed state of Zone
0.
6. The 5th average period the ALS voltage averages to Zone 2. The Averager Output remains at Zone 0. Since the Up Only
algorithm is chosen the backlight current remains at the Zone 1 target even though this is the 3rd consecutive average period
that the Averager Output has shown a change since the initial Zone 1.
7. The 6th average period the ALS voltage averages to Zone 2. The Averager Output changes from Zone 0 to Zone 2.
8. The 7th average period the ALS voltage averages to Zone 3. The Averager Output remains at Zone 2.
9. The 8th average period the ALS voltage averages to Zone 3. The Averager Output remains at Zone 2. Since this is the 3rd
average period that the Averager Output has shown a change in the up direction, the backlight current is forced to change to
the current Averager Output (Zone 2's) target current.
10. The 9th average period the ALS voltage averages to Zone 3. The Averager Output changes from Zone 2 to Zone 3. Since this
is a change in the increasing Zone direction, and is a consecutive change following a new backlight target current transition,
the backlight current is again 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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