LM3530 datasheet(15/50 Pages) TI1

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Zone0

Zone1

Zone2

Zone3

Zone4

Zone0

Zone1

Zone2

Zone3

Zone4

1 Ave

Period

Zone0

Zone1

Zone2

Zone3

Zone4

Averager Output

LED Brightness

Zone

ALS Input

Zone0

Zone1

Zone2

Zone3

Zone4

Averager

Output

1 Ave

Period

tBRGT-CHANGE =

2.75 Average

Time

tBRGT-CHANGE =

1.75 Average Time

LM3530

www.ti.com

SNVS606L – JUNE 2009 – REVISED DECEMBER 2014

Figure 30. Ambient Light Input To Backlight

Transition

Figure 31. Perceived Brightness Change Time

8.3.6

Zone Boundary Settings

Registers 0x60, 0x61, 0x62, and 0x63 set the 4 zone boundaries (thresholds) for the ALS inputs. These 4 zone

boundaries create 5 brightness zones which map over to 5 separate brightness zone targets (see Figure 27).

Each 8-bit zone boundary register can set a threshold from typically 0 to 1 V with linear step sizes of

approximately 1/255 = 3.92 mV. Additionally, each zone boundary has built in hysteresis which can be either

lower or higher then the programmed Zone Boundary depending on the last direction (either up or down) of the

ALS input voltage.

8.3.7

Zone Boundary Trip Points and Hysteresis

For each zone boundary setting, the trip point will vary above or below the nominal set point depending on the

direction (either up or down) of the ALS input voltage. This is designed to keep the ALS input from oscillating

back and forth between zones in the event that the ALS voltage is residing near to the programmed zone

boundary threshold. The Zone Boundary Hysteresis will follow these 2 rules:

1. If the last zone transition was from low to high, then the trip point (VTRIP) will be VZONE_BOUNDARY - VHYST/2,

where VZONE_BOUNDARY is the zone boundary set point as programmed into the Zone Boundary registers, and

VHYST is typically 7 mV.

2. If the last zone transition was from high to low then the trip point (VTRIP) will be VZONE_BOUNDARY + VHYST/2.

Figure 32 details how the LM3530 ALS Input Zone Boundary Thresholds vary depending on the direction of the

ALS input voltage.

Referring to Figure 32, each numbered trip point shown is determined from the direction of the previous ALS

zone transition.

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