LM3532TMX-40ANOPB National Semiconductor Corporation, LM3532TMX-40ANOPB Datasheet - Page 21

• 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

DOWN DELAY
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 were programmed with 0x00 (3 extra
delays), then the Averager Output would need to see 6 con-
secutive changes in decreasing Zones (or 6 consecutive
average periods that changed and remained lower), before
the backlight current was programmed to the lower zones tar-
get current. Referring to
is enabled and the ALS Down Delay register is programmed
with 0x02 (5 extra delays, 8 average period total delay for
downward changes in the backlight target current):
1.
2.
When the ALS is enabled the ALS fast startup (1.1 ms
average period) quickly brings the Averager Output to the
correct zone. This takes 3 fast average periods or
approximately 3.3 ms.
The first average period the ALS averages to Zone 3.
Figure
11, assume that Down Delay
FIGURE 10. Direct ALS Control
21
3.
4.
5.
6.
7.
8.
The second average period the ALS averages to Zone 2.
The Averager Output remains at Zone 3.
The 3rd through 7th average period the ALS input
averages to Zone 2, and the Averager Output stays at
Zone 2.
The 8th average period the ALS input averages to Zone
4. The Averager Output remains at Zone 2.
The 9th and 10th average periods the ALS input
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.
The 11th average period the ALS input 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 since the change from Zone
2, the backlight current transitions to Zone 4's target
current.
The 12th through 26th average periods the ALS input
averages to Zone 2. The Averager Output remains at
Zone 2. At the start of average period #20 the Down
Delay algorithm has shown the required 8 average period
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