LM3532 datasheet(21/52 Pages) TI2

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VALS_

Enable ALS

Zone 4

Zone 3

Zone 2

Zone 1

Zone 0

Current Average Zone

*Note:it takes a full

average period to

generate an averager

output value

ILED

Zone 4 Brightness Target

Averager Ouput

ALS Fast Start-Up

Average

Period #

LED Current Run Time

Ramp Down

Zone 3 Brightness Target

Zone 2 Brightness Target

Zone 1 Brightness Target

Zone 4 Brightness Target

LED Current Run

Time Ramp Up

LM3532

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SNVS653E – JULY 2011 – REVISED AUGUST 2015

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.

Because 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 19. Direct ALS Control

7.4.11 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

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 20, assume

that Down Delay 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. When the ALS is enabled the ALS fast start-up (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.

2. The first average period the ALS averages to Zone 3.

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