LM3532 datasheet(18/52 Pages) TI2

18 / 52 page

ALS Enabled

I2C Write

VALS

(active input is sampled)

tCONV = 140 Ps

ADC Register

(Read Only, Updated every tCONV)

Sample

ADC Average Register

(Read Only, Updated every tAVERAGE)

tAVERAGE

(set via bits [2:0] of the ALS

Configuration Register)

0x00

Sample 1 + Sample 2 + Sample 3 + « 6DPSOH Q

Con-

version

n + 1

Average Period #1

Average Period #2

Con-

version

Con-

version

Con-

version

Con-

version

ADC Register

Averager

ALS Average Time

(ALS Configuration

ADC

(7.142ksps)

ALS Configuration

Read Back UP

Only Register

Direct ALS Control

(Up and Down Delay

= 3 x tAVE)

Up Only Control

(Up Delay = 3 x tAVE)

4 x tAVE to 35 x tAVE)

Up Delay = 3 x tAVE

Read Back

Ambient Light

Zone Register

ALS Input Select

(ALS Configuration

ALS1

ALS2

ALS Brightness

Control Target

Read Back

Brightness Zone

ADC Average

Down Delay Control

Averager

Output

(Down Delay =

LM3532

SNVS653E – JULY 2011 – REVISED AUGUST 2015

www.ti.com

Figure 16. ALS Functional Block Diagram

7.4.10.6 ALS Input Select and ALS ADC Input

The internal 8-bit ADC digitizes the active ambient light sensor inputs (ALS1 or ALS2). The active ALS input is

determined by the bit settings of the ALS input select bits, bits [7:6] in the ALS Configuration register. The active

ALS input can be the average of ALS1 and ALS2, the maximum of ALS1 and ALS2, ALS1 only, or ALS2 only.

Once the ALS input select stage selects the active ALS input, the result is sent to the internal 8-bit ADC. For

example, if the active ALS input select is set to be the average of ALS1 and ALS2, then the voltage at ALS1 and

ALS2 is first averaged, then applied to the ADC. The output of the ADC (ADC Register) is the digitized average

value of ALS1 and ALS2.

The LM3532 device's internal ADC samples at 7.143 ksps. ADC timing is shown in Figure 17. When the ALS is

enabled (ALS Configuration Register bit [3] = 1) the ADC begins sampling and converting the active ALS input.

Each conversion takes 140 µs. After each conversion the ADC register is updated with new data.

Figure 17. ADC Timing

7.4.10.7 ALS ADC Readback

The digitized value of the LM3532 device's ADC is read back from the ADC Readback Register. Once the ALS is

enabled, the ADC begins converting the active ALS input and updating the ALS Readback Register every 140

µs. The ADC Readback register contains the updated data after each conversion.

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