ISL29033

9

FN7656.2

February 25, 2013

2. Interrupt Persist: Bits 1 and 0. The interrupt pin and the

interrupt flag are triggered or set when the data sensor

reading is out of the interrupt threshold window after m

consecutive number of integration cycles (Table 4). The

interrupt persist bits determine m.

Command Register II 01 (Hex)

The second command register has the following functions:

1. Resolution: Bits 3 and 2. Bits 3 and 2 determine the ADC

resolution and the number of clock cycles per conversion

(Table 5). Changing the number of clock cycles does more than

just change the resolution of the device; it also changes the

integration time, which is the period during which the

analog-to-digital (A/D) converter samples the photodiode

current signal for a measurement.

2. Range: Bits 1 and 0. The Full Scale Range (FSR) can be

Data Registers (02 Hex and 03 Hex)

The device has two 8-bit read-only registers to hold the data from

LSB to MSB for the ADC (Table 7). The most significant bit (MSB)

is accessed at 03 hex, and the least significant bit (LSB) is

accessed at 02 hex. For 16-bit resolution, the data is from D0 to

D15; for 12-bit resolution, the data is from D0 to D11; for 8-bit

resolution, the data is from D0 to D7. The registers are refreshed

after every conversion cycle.

Interrupt Registers (04, 05, 06 and 07 Hex)

Registers 04 and 05 hex set the low (LO) threshold for the

interrupt pin and the interrupt flag. Register 04 hex is the LSB,

and Register 05 hex is the MSB. By default, the interrupt

threshold LO is 00 hex for both LSB and MSB.

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

interrupt pin and the interrupt flag. Register 06 hex is the LSB,

and Register 07 hex is the MSB. By default, the interrupt

threshold HI is FF hex for both LSB and MSB.

Calculating Lux

The ISL29033 ADC output codes, DATA, are directly proportional

to lux in ambient light sensing, as shown in Equation 1.

a, is determined by the full scale range and the ADC maximum

output counts. The constant is independent of the light sources

(fluorescent, incandescent and sunlight) because the light source

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.

the maximum output counts from the ADC.

The transfer function used for n-bits ADC is as shown in

Equation 3:

In this equation, n = 4, 8, 12 or 16 and is the number of ADC bits

represents the maximum number of counts possible from the

ADC output. Data is the ADC output stored in data

Registers 02 hex and 03 hex.

Integration and Conversion Time

shown in Equation 4.

In this equation, n is the number of bits of resolution, and n = 4,

value of n can be programmed at the command register, Register

01 (hex), Bits 3 and 2 (Table 8).

TABLE 4. INTERRUPT PERSIST

BIT 1:0

NUMBER OF INTEGRATION CYCLES

00

1

01

4

10

8

11

16

TABLE 5. ADC RESOLUTION DATA WIDTH

BITS 3:2

NUMBER OF CLOCK CYCLES

n-BIT ADC

00

16

01

12

10

8

11

4

TABLE 6. RANGE/FSR LUX

BITS 1:0

k

RANGE(k)

FSR (LUX) @ ALS SENSING

00

1

Range1

125

01

2

Range2

500

10

3

Range3

2,000

11

4

Range4

8,000

TABLE 7. DATA REGISTERS

ADDRESS

(HEX)

CONTENTS

02

D0 is LSB for 4-, 8-, 12- or 16-bit resolution; D3 is MSB for

4-bit resolution; D7 is MSB for 8-bit resolution

03

D15 is MSB for 16-bit resolution; D11 is MSB for 12-bit

resolution

α DATA

×

=

(EQ. 1)

α

Range k

()

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

=

(EQ. 2)

(EQ. 3)

Range k

()

2

n

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

DATA

×

=

2

n

1

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

×

2

n

655kHz 499k

Ω

×

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

×

==

(EQ. 4)