LM3532TMX-40ANOPB National Semiconductor Corporation, LM3532TMX-40ANOPB Datasheet - Page 20

• Manufacturer Part Number: LM3532TMX-40ANOPB
• Description: High Efficiency White Led Driver With Programmable Ambient Light Sensing Capability And I2c-compatible Interface
• Manufacturer: National Semiconductor Corporation

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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 sec-
tion.
In the example of
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 pre-
vious full average period, and the target backlight current that
is controlled by the ALS Interface. The following steps detail
the Direct ALS algorithm:
1.
2.
3.
4.
5.
6.
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.
The 1st average period the ALS voltage averages to
Zone 4.
The 2nd average period the ALS voltage averages to
Zone 3.
The 3rd average period the ALS voltage averages to
Zone 3 and the Averager Output shows a change from
Zone 4 to Zone 3.
The 4th average period the ALS voltage averages to
Zone 2 and the Averager Output remains at its changed
state of Zone 3.
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.
Figure 10
the plot shows the ALS voltage,
20
7.
8.
9.
10. The 9th average period the ALS voltage averages to
11. The 10th average period the ALS voltage averages to
12. The 11th average period the ALS voltage averages to
13. The 12th average period the ALS voltage averages to
14. The 13th average period the ALS voltage averages to
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.
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.
The 8th average period the ALS voltage averages to
Zone 3. The Averager Output changes from Zone 2 to
Zone 3.
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.
Zone 4. The Averager Output remains at Zone 3.
Zone 4. The Averager Output changes to Zone 4.
Zone 4. The Averager Output remains at Zone 4.
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.