ISL29013 查看數據表（PDF） - Renesas Electronics

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ISL29013

Light-to-Digital Output Sensor with High Sensitivity, Gain Selection, Interrupt Function and I2C Interface

Renesas Electronics 

ISL29013

When using the Internal Timing Mode, fOSC and n-bits

resolution determine the integration time. tINT is a function of

the number of clock cycles and fOSC as shown in Equation 9:

tINT = 2m  f--o--1--s---c-

for Internal Timing Mode only

(EQ. 9)

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

2m therefore is the number of clock cycles. n can be

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

Since fOSC is dual speed depending on the Gain/Range bit,

tINT is dual time. The integration time as a function of REXT is

shown in Equation 10:

tINT1 = 2m  3----2---7----k---H--R---z--E----X---T-1---0---0----k------

(EQ. 10)

tINT1 is the integration time when the device is configured for

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

Range2.

tINT2 = 2m  6----5---5----k---H--R---z--E----X---T-1---0---0----k------

(EQ. 11)

tINT2 is the integration time when the device is configured for

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

Range4.

TABLE 13. INTEGRATION TIMES FOR TYPICAL REXT VALUES

REXT

(k

RANGE1

RANGE2

n = 15-BIT n = 11-BIT

50

100

6.4

100**

200

13

200

400

26

500

1000

64

*Integration time in milliseconds

**Recommended REXT resistor value

RANGE3

RANGE4

n = 11-BIT

n=3

3.2

0.013

6.5

0.025

13

0.050

32

0.125

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

sync_I2C commands to complete one measurement. The 1st

sync_I2C command starts the conversion of the diode array 1.

The 2nd sync_I2C completes the conversion of diode array 1

and starts the conversion of diode array 2. The 3rd sync_I2C

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

count DATA, and starts over again to commence conversion of

diode array 1.

The integration time, tINT, is the sum of two identical time

intervals between the three sync pulses. tINT is determined by

Equation 12:

tINT = k-f--O-O----SS---C-C--

(EQ. 12)

fwrohmereTiKmOeSr CdaistathreegnisutmerbaenrdoffOinStCernisatlhceloincktecrnyaclleIs2Cobotpaeinreadting

frequency

The internal oscillator, fOSC, operates identically in both the

internal and external timing modes, with the same dependence

on REXT. However, in External Timing Mode,

clock cycles per integration is no longer fixed

the number

at 2n. The

of

number of clock cycles varies with the chosen integration time,

and is limited to 216 = 65,536. In order to avoid erroneous lux

readings the integration time must be short enough not to allow

an overflow in the counter register.

tINT  6---f-5-O--,--5S---3-C---5-

(EQ. 13)

fOSC = 327kHz*100k/REXT. When Range/Gain is set to

Range1 or Range2.

fosc = 655kHz*100k/REXT. When Range/Gain is set to

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 0ms to

k*16.66ms (k = 1,2...ki) is zero. Similarly, setting the 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.

Maximum Ambient Intensity Condition

The operation of ambient light sensing (ALS) within the

ISL29013 utilizes two diodes, D1 and D2. The diodes are

measured sequentially and their outputs are converted with an

ADC. The output of the ALS is the difference between these

two measurements. In typical applications, the ISL29013 is

installed behind a dark cover window. In this low-light

condition, both D1 and D2 operate linearly and the ALS output

is linear as well (Figures 18 and 19). In brighter environments,

however, D1 and D2 can be subject to saturation. As the

ambient light grows bright enough to subject one or both

diodes to saturation, the ALS count (output) decreases and

eventually reaches zero in deep saturation (Figure 17). When

using the ISL29013 in high lux applications, be sure to choose

a low REXT to avoid saturation at Range4, the lowest gain. For

example, REXT = 25k is recommended with ambient light

near 100,000 lux. If you are operating the ISL29013 at a lower

range/higher gain and detect a zero output, the firmware

should change the range and recheck the ALS count. One of

two situations will be identified. If the output is nonzero, the

ISL29013 is saturated. If the output remains zero, the

ISL29013 is in a totally dark environment.

FN6485 Rev 3.00

November 11, 2011

Page 8 of 14

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