10

FN6467.3

February 4, 2010

Registers 06 and 07 hex set the high (HI) threshold for the

interrupt pin and the interrupt flag. 06 hex is the LSB and 07

hex is the MSB. By default, the Interrupt threshold HI is FF

hex for both LSB and MSB.

Test Register (08 hex)

Register 8 is a reserved register that holds 00h during

normal operation.

Calculating Lux

The ISL29011’s ADC output codes, DATA, are directly

proportional to lux in the ambient light sensing.

determined by the Full Scale Range and the ADC’s

maximum output counts. The constant is independent on the

light sources (fluorescent, incandescent and sunlight)

because of the light sources’ IR component is removed

during the light signal process. The constant can also be

viewed as the sensitivity: the smallest lux measurement the

device can measure as shown in Equation 2.

maximum output counts from the ADC.

The transfer function used for n-bit ADC becomes

Equation 3:

Here, n = 4, 8, 12 or 16. This is the number of ADC bits

maximum number of counts possible from the ADC output.

Data is the ADC output stored in the data registers (02 hex

and 03 hex).

Integration and Conversion Time

where n is the number of bits of resolution and n = 4, 8, 12 or

programmed at the command register 01(hex) bits 3 and 2.

referenced to 499k

Ω as shown in Equations 5 and 6:

Noise Rejection

In general, integrating type ADC’s have excellent

noise-rejection characteristics for periodic noise sources

whose frequency is an integer multiple of the conversion

rate. For instance, a 60Hz AC unwanted signal’s sum from

device’s integration time to be an integer multiple of the

periodic noise signal, greatly improves the light sensor

output signal in the presence of noise.

ADC Output in IR Sensing

The ISL29011’s ADC output codes, DATA, are directly

proportional to the IR intensity received in the IR sensing.

changes with the spectrum of background IR noise like

sunlight and incandescent light. The

β also changes with the

ADC’s range and resolution selections.

ADC Output in Proximity Sensing

In the proximity sensing, the ADC output codes, DATA, are

directly proportional to the total IR intensity from the

background IR noise and from the IR LED driven by the

ISL29011.

Here,

The constant

γ depends on the spectrum of the used IR LED

IR intensity which is emitted from the IR LED and reflected

decreases with the square of the distance between the

object and the sensor.

the ADC output directly decreases with the distance. If there

is significant background IR noise, ISL29011 offers two

schemes to reduce the effect. The first way is do a proximity

sensing using Scheme 0, immediately followed by an IR

sensing. The differential reading of ADC outputs from the

proximity and IR sensing will then reduce the effect of

background IR noise and directly decrease with the distance

between the object and the sensor. The second way is to do

TABLE 11. INTEGRATION TIME OF n-BIT ADC

(k

Ω)

n = 16-BIT

(ms)

n = 12-BIT

(ms)

n = 8-BIT

(µs)

n = 4-BIT

(µs)

250

45

2.812

175.5

10.8µs

499**

90

5.63

351

21.6µs

α DATA

×

=

(EQ. 1)

α

Range k

()

----------------------------

=

(EQ. 2)

(EQ. 3)

Range k

()

2

n

---------------------------

DATA

×

=

2

n

1

--------------

×

2

n

725kHz 499k

Ω

×

----------------------------------------------

×

==

(EQ. 4)

(EQ. 5)

Range

499k

Ω

------------------

Range k

()

×

=

(EQ. 6)

499k

Ω

------------------

725

×

kHz

=

β E

IR

×

=

(EQ. 7)

β E

IR

×γ E

LED

×

+

=

(EQ. 8)

ISL29011