LM3532 datasheet(19/52 Pages) TI2

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ALS Enable

ALS Start-Up Fast

Average Period

(1.1 ms)

VALS_X

Zone 0

ALS Zone

I2C

ILED_

Zone 0

Zone Target x

VALS_Y

Start-Up

Ramp Rate

Zone Target y

Normal ALS

Average Period

Zone X

Zone Y

Run Time

Ramp Rate

LM3532

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SNVS653E – JULY 2011 – REVISED AUGUST 2015

7.4.10.8 ALS Averaging

ALS averaging is used to filter out any fast changes in the ambient light sensor inputs. This prevents the

backlight current from constantly changing due to rapid fluctuations in the ambient light. There are 8 separate

averaging periods available for the ALS inputs (see Table 17). During an average period the ADC continually

samples at 7.143 ksps. Therefore, during an average period, the ALS Averager output is the average of

7143/tAVE.

7.4.10.9 ALS ADC Average Readback

The output of the LM3532's averager is read back via the Average ADC Register. This data is the ADC register

data, averaged over the programmed ALS average time.

7.4.10.10 Initializing the ALS

On initial start-up of the ALS Block, the Ambient Light Zone defaults to Zone 0. This allows the ALS to start off in

a predictable state. The drawback is that Zone 0 is often not representative of the true ALS Brightness Zone

because the ALS inputs can get to their ambient light representative voltage much faster then the backlight is

allowed to change. In order to avoid a multiple average time wait for the backlight current to get to its correct

state, the LM3532 switches over to a fast average period (1.1 ms) on ALS startup. This quickly brings the ALS

Brightness Zone (and the backlight current) to its correct setting (see Figure 18).

Figure 18. ALS Start-up Sequence

7.4.10.11 ALS Operation

The LM3532's Ambient Light Sensor Interface has 3 different algorithms that can be used to control the ambient

light to backlight current response.

ALS Algorithms

1. Direct ALS Control

2. Down Delay

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