8

FN6485.0

February 13, 2008

INTEGRATION TIME IN INTERNAL TIMING MODE

This timing mode is programmed in the command register

00(hex) Bit 5. Most applications will be using this timing

Equation 9:

m = 4, 8, 12, and16. n is the number of bits of resolution.

programmed at the command register 00(hex) Bits 1 and 0.

is shown in Equation 10:

for Internal Timing Mode and Gain/Range is set to Range1

or Range2.

for Internal Timing Mode and Gain/Range is set to Range3

or Range4.

INTEGRATION TIME IN EXTERNAL TIMING MODE

This timing mode is programmed in the command register

00(hex) Bit 5. External Timing Mode is recommended when

integration time can be synchronized to an external signal

such as a PWM to eliminate noise.

To read the light count DATA output, the device needs three

pules ends the conversion of diode array 2, outputs the light

count DATA, and starts over again to commence conversion

of diode array 1.

by Equation 12:

operating frequency

internal and external timing modes, with the same

the number of clock cycles per integration is no longer fixed

avoid erroneous lux readings the integration time must be

short enough not to allow an overflow in the counter register.

Range1 or Range2.

Range3 or Range4.

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 integration

time. 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.

Flat Window Lens Design

A window lens will surely limit the viewing angle of the

ISL29013. The window lens should be placed directly on top

of the device. The thickness of the lens should be kept at

minimum to minimize loss of power due to reflection and

also to minimize loss of loss due to absorption of energy in

the plastic material. A thickness of t = 1mm is recommended

for a window lens design. The bigger the diameter of the

window lens the wider the viewing angle is of the ISL29013.

Table 14 shows the recommended dimensions of the optical

window to ensure both 35° and 45° viewing angle. These

dimensions are based on a window lens thickness of 1.0mm

and a refractive index of 1.59.

TABLE 13. INTEGRATION TIMES FOR TYPICAL REXT VALUES

(k

Ω)

RANGE1

RANGE2

RANGE3

RANGE4

n = 15-BIT

n = 11-BIT

n = 11-BIT

n = 3

50

100

6.4

3.2

0.013

100**

200

13

6.5

0.025

200

400

26

13

0.050

500

1000

64

32

0.125

*Integration time in milliseconds

**Recommended

t

INT

2

m

1

f

osc

----------

×

=

(EQ. 9)

for Internal Timing Mode only

t

m

R

EXT

327kHz

100k

Ω

×

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

×

=

(EQ. 10)

t

m

R

EXT

655kHz

100k

Ω

×

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

×

=

(EQ. 11)

t

INT

k

OSC

f

OSC

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

=

(EQ. 12)

t

INT

65,535

f

OSC

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

<

(EQ. 13)

ISL29013