LM3533 Datasheet, PDF (26/53 Pages) Texas Instruments – Complete Lighting Power Solution for Smartphone Handsets

LM3533
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.
FIGURE 12. ALS Up-Only Control
30135712
DOWN-DELAY CONTROL
The Down-Delay algorithm uses all the same rules from the ALS RULES section, except it provides for adding additional average
period delays required for decreasing transitions of the Averager Output, before the LED current is programmed to a lower zone
target current. The additional average period delays are programmed via the ALS Down Delay register. The register provides 32
settings for increasing the down delay from 3 extra (code 00000) up to 34 extra (code 11111). For example, if the down delay
algorithm is enabled, and the ALS Down Delay register was programmed with 0x00 (3 extra delays), then the Averager Output
would need to see 6 consecutive changes in decreasing Zones (or 6 consecutive average periods that changed and remained
lower), before the backlight current was programmed to the lower zones target current. Referring to Figure 13, assume that Down
Delay is enabled, and the ALS Down Delay register is programmed with 0x02 (5 extra delays, or 8 average period total delays for
downward changes in the backlight target current):
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 first average period the ALS voltage averages to Zone 3.
3. The second average period the ALS voltage averages to Zone 2. The Averager Output remains at Zone 3.
4. The 3rd through 7th average period the ALS voltage averages to Zone 2, and the Averager Output stays at Zone 2.
5. The 8th average period the ALS voltage averages to Zone 4. The Averager Output remains at Zone 2.
6. The 9th and 10th average periods the ALS voltage averages to Zone 4. The Averager Output is at Zone 4. Since the Averager
Output increased from Zone 2 to Zone 4 and the required Down Delay time was not met (8 average periods), the backlight
current was never changed to the Zone 2's target current.
7. The 11th average period the ALS voltage averages to Zone 2. The Averager Output remains at Zone 4. Since this is the 3rd
consecutive average period where the Averager Output has shown a change (increasing direction) since the change from
Zone 2, the backlight current transitions to Zone 4's target current.
26
Copyright © 1999-2012, Texas Instruments Incorporated