ISL76683

10

FN7697.1

January 31, 2011

2. Range/Gain; Bits 3 and 2. The Full Scale Range can be

has four possible values, Range(k) where k is 1 through 4.

Table 9 lists the possible values of Range(k) and the resulting

3. Interrupt persist; Bits 1 and 0. The interrupt pin and the

interrupt flag is triggered/set when the data sensor reading is

out of the interrupt threshold window after m consecutive

number of integration cycles. The interrupt persist bits

determine m.

Interrupt Threshold HI Register 02(hex)

This register sets the HI threshold for the interrupt pin and the

interrupt flag. By default, the Interrupt threshold HI is FF(hex).

The 8-bit data written to the register represents the upper MSB of

a 16-bit value. The LSB is always 00(hex).

Interrupt Threshold LO Register 03(hex)

This register sets the LO threshold for the interrupt pin and the

interrupt flag. By default, the Interrupt threshold LO is 00(hex).

The 8-bit data written to the register represents the upper MSB of

a 16-bit value. The LSB is always 00(hex).

Sensor Data Register 04(hex) and 05(hex)

When the device is configured to output a 16-bit data, the least

significant byte is accessed at 04(hex), and the most significant

byte can be accessed at 05(hex). The sensor data register is

refreshed after every integration cycle.

Timer Data Register 06(hex) and 07(hex)

Note that the timer counter value is only available when using the

External Timing Mode. The 06(hex) and 07(hex) are the LSB and

MSB respectively of a 16-bit timer counter value corresponding to

the most recent sensor reading. Each clock cycle increments the

counter. At the end of each integration period, the value of this

eliminate noise introduced by slight timing errors caused by

imprecise external timing. Microcontrollers, for example, often

cannot provide high-accuracy command-to-command timing,

and the timer counter value can be used to eliminate the

resulting noise.

Calculating Lux

The ISL76683’s output codes, DATA, are directly proportional to lux.

The proportionality constant

α is determined by the Full Scale

Range, FSR, and the n-bit ADC, which is user defined in the

command register. The proportionality constant can also be

viewed as the resolution; The smallest lux measurement the

device can measure is

α.

Full Scale Range, FSR, is determined by the software

programmable Range/Gain, Range(k), in the command register

100k

Ω.

The transfer function effectively for each timing mode becomes:

INTERNAL TIMING MODE

EXTERNAL TIMING MODE

n = 4, 8, 12, or 16. This is the number of clock cycles

programmed in the command register.

Range(k) is the user defined range in the Gain/Range bit in the

command register.

DATA is the output sensor reading in number of counts available

at the data register.

Internal Timing Mode. For the External Timing Mode, the

maximum number of counts is stored in the data register named

COUNTER.

COUNTER is the number increments accrued for between

integration time for External Timing Mode.

TABLE 9. RANGE/GAIN TYPICAL FSR LUX RANGES

BITS

3:2

k

RANGE

(k)

FSR LUX

RANGE@

FSR LUX

RANGE@

FSR LUX

RANGE@

0:0

1

973

973

1946

195

0:1

2

3892

3892

7784

778

1:0

3 15,568

15,568

31,136

3114

1:1

4 62,272

62,272

124,544

12,454

TABLE 10. INTERRUPT PERSIST

BITS 1:0

NUMBER OF INTEGRATION CYCLES

0:0

1

0:1

4

1:0

8

1:1

16

TABLE 11. DATA REGISTERS

ADDRESS

(hex)

CONTENTS

04

Least-significant byte of most recent sensor reading.

05

Most-significant byte of most recent sensor reading.

06

Least-significant byte of timer counter value corresponding to

most recent sensor reading.

07

Most-significant byte of timer counter value corresponding to

most recent sensor reading.

E

α DATA

×

=

(EQ. 1)

α

FSR

2

n

-----------

=

(EQ. 2)

(EQ. 3)

FSR

Range k

() 100kΩ

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

×

=

(EQ. 4)

E

Range k

() 100kΩ

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

×

2

n

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

DATA

×

=

(EQ. 5)

E

Range k

() 100kΩ

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

×

COUNTER

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

DATA

×

=