ILED = ILED_FS u ZoneTarget0 = 25 mA u 0.336% | 84 PA.

Ambient Light (lux)

Vals_ref

= 1V

ZB3

ZB0

ZB1

ZB2

Zone 0

Zone 4

Zone 3

Zone 2

Zone 1

LED Driver Input Code (0-127)

Full

Scale

Z0T

Z4T

Z3T

Z2T

Z1T

21

LM3535

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Zone Boundary 0 = 200 mV

Zone Boundary 1 = 400 mV

Zone Boundary 2 = 600 mV

Zone Boundary 3 = 800 mV

These Zone Boundary Registers are all 8-bit (readable and writable) registers. By default, the first zone (Z0) is

defined between 0 and 200 mV, default for Z1 is defined between 200 mV and 400 mV, Z2 is defined between

400 mV and 600 mV, Z3 is defined between 600 mV and 800 mV, and Z4 is defined between 800 mV and 1 V.

The default settings for the 5 Zone Target Registers are 0x19, 0x33, 0x4C, 0x66, and 0x7F. This corresponds to

LED brightness settings of 84 µA, 164 µA, 1.45 mA, 6.17 mA and 25 mA of current, respectively. See Figure 31.

Figure 31. ALS Zone to LED Brightness Mapping

8.2.2.1.2.1

ALS Configuration Example

As an example, assume that the APDS-9005 is used as the ambient light sensing photo diode with its output

connected to the ALS input. The ALS Resistor Select Register (Address 0x51) is loaded with 0x40 which

configures the ALS input for a 2.32-k

Ω internal pulldown resistor (see Table 2). This gives the output of the

APDS-9005 a typical voltage swing of 0 to 875mV with a 0 to 1k LUX change in ambient light (0.875mV/Lux).

Next, the Configuration Register (Address 0x20) is programmed with 0xDC, the ALS Control Register (Address

0x50) programmed to 0x40 and the Control Register is programmed to 0x3F . This configures the device ALS

interface for:

•

Ambient Light Current Control for BankA enabled

•

ALS circuitry enabled

•

Assigns D53 and D62 to bankA

•

Sets the ALS Averaging Time to 400 ms

Next, the Control Register (Address 0x10) is programmed with 0x3F which enables the 6 LEDs via the I2C-

compatible interface.

Now assume that the APDS-9005 ambient light sensor detects a 100 LUX ambient light at its input. This forces

the ambient light sensor output (and the ALS input) to 87.5 mV corresponding to Zone 0. Since Zone 0 points to

the brightness code programmed in Zone Target Register 0 (loaded with code 0x19), the LED current becomes:

(2)