LM3533 Datasheet, PDF (23/53 Pages) Texas Instruments – Complete Lighting Power Solution for Smartphone Handsets

LM3533
FIGURE 9. ADC Timing
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ALS AVERAGER
Once digitized the output of the ADC is sent into the ALS averager. The averager will compute 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 9). After every average period the Averager Output stores the
information for which brightness zone the ALS input voltage resides in (see Figure 8).
INITIALIZING THE ALS
On initial startup of the ALS Interface, the Ambient Light Zone will default 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, since 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 startup. This will quickly bring the ALS Brightness Zone (and the backlight current) to its correct setting (see Figure 10).
FIGURE 10. ALS Startup Sequence
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