LM3533 datasheet(21/63 Pages) TI1

21 / 63 page

ALS Enable

ALS Startup Fast Average Period

(1.1 ms)

VALS_X

Zone 0

ALS Zone

ILED

Zone

Zone Target x

VALS_Y

Startup

Ramp Rate

Zone Target y

Normal ALS

Average Period

Zone X

Zone Y

Run Time

Ramp Rate

LM3533

www.ti.com

SNOSC68C – APRIL 2012 – REVISED SEPTEMBER 2015

Device Functional Modes (continued)

7.4.8.5 ALS Averager

Once digitized the output of the ADC is sent into the ALS averager. The averager computes the average of the

number of samples taken over the programmed average period. The ALS average times are set via bits [5:3] in

the ALS Configuration Register. The output of the ALS average can be read back via the ADC Average register

(address 0x38). With the ALS Enable bit set, the ADC Average register is updated after each average period

(see Figure 28). After every average period the Averager Output stores the information for which brightness zone

the ALS input voltage resides in (see Figure 27).

7.4.8.6 Initializing the ALS

On initial start-up of the ALS Interface, 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,

as the ALS input can get to its ambient light representative voltage much faster than the LED current is allowed

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

LM3533 switches over to a fast average period (1.1 ms) during the ALS start-up. This quickly brings the ALS

Brightness Zone (and the backlight current) to its correct setting (see Figure 29).

Figure 29. ALS Start-up Sequence

7.4.8.7 ALS Algorithms

There are three ALS algorithms that can be selected independently by each ALS Mapper (ALSM1, ALSM2, and

ALSM3) (see Table 23). The ALS algorithms are: direct, up only, and down delay.

7.4.8.8 ALS Rules

For each algorithm, the ALS follows these basic rules:

1. For the ALS Interface to force a change in the backlight current (to a higher zone target), the averager output

must have shown an increase for 3 consecutive average periods, or an increase and a remain at the new

zone for 3 consecutive average periods.

2. For the ALS Interface to force a change in the backlight current (to a lower zone target), the averager output

must have shown a decrease for 3 consecutive average periods, or a decrease and remain at the new zone

for 3 consecutive average periods.

3. If condition 1 or 2 above is satisfied, and during the next average period the averager output changes again

in the same direction as the last change, the LED current immediately changes at the beginning of the next

average period.

Submit Documentation Feedback

Product Folder Links: LM3533

LM3533 датащи(PDF) 21 Page - Texas Instruments

LM3533 датащи(HTML) 21 Page - Texas Instruments

Html Pages

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63

датащи скачать

ссылки URL