ISL29043

9

FN7935.0

February 9, 2012

Principles of Operation

as 0b100010<x>, where “0b” signifies binary notation and x

represents the logic level on pin ADDR0.

always drives the SCL (clock) line, while either the master or the

with the master asserting a start condition (SDA falling while SCL

remains high). The first transmitted byte is initiated by the

master and includes 7 address bits and a R/W bit. The slave is

responsible for pulling SDA low during the ACK bit after every

transmitted byte.

condition (SDA rising while SCL remains high).

Photodiodes and ADCs

The ISL29043 contains two photodiode arrays which convert

photons (light) into current. The ALS photodiodes are constructed to

mimic the human eye’s wavelength response curve to visible light

(see Figure 11). The ALS photodiodes’ current output is digitized by a

12-bit ADC in 100ms. These 12 bits can be accessed by reading

completed.

The ALS converter is a charge-balancing integrating 12-bit ADC.

Charge-balancing is best for converting small current signals in the

presence of periodic AC noise. Integrating over 100ms highly rejects

both 50Hz and 60Hz light flicker by picking the lowest integer

number of cycles for both 50Hz/60Hz frequencies.

The proximity sensor is an 8-bit ADC, which operates in a similar

fashion. When proximity sensing is enabled, the IRDR pin will

drive the internal infrared LED, the emitted IR reflects off an object

(e.g., a human head) back into the ISL29043, and a sensor

converts the reflected IR wave to a current signal in 0.54ms. The

ADC subtracts the IR reading before and after the LED is driven

(to remove ambient IR such as sunlight), and converts this value

to a digital count stored in Register 0x8.

The ISL29043 is designed to run two conversions concurrently: a

proximity conversion and an ALS (or IR) conversion. Please note that

because of the conversion times, the user must let the ADCs perform

PROX_DATA (wait 0.54ms) or ALSIR_DT1/2 (wait 100ms). The timing

between ALS and Prox conversions is arbitrary (as shown in Figure 5).

The ALS runs continuously with new data available every 100ms. The

proximity sensor runs continuously with a time between conversions

decided by PROX_SLP (Register 1 Bits [6:4]).

START

W A

A

A6 A5 A4 A3 A2 A1 A0 W A R7 R6 R5 R4 R3 R2 R1 R0 A

A6 A5 A4 A3 A2 A1 A0 W A

AA

A D7 D6 D5 D4 D3 D2 D1 D0

13

5

7

13

57

12 3

4 5

6

9

2

4

6

STOP START

SDA DRIVEN BY MASTER

DEVICE ADDRESS

SDA DRIVEN BY ISL29043

DATA BYTE0

REGISTER ADDRESS

SLAVE

DEVICE ADDRESS

SDA DRIVEN BY MASTER

SDA DRIVEN BY MASTER

24

68 92

4

6

8 9

7

8

1

357

8

9

MASTER

(ISL29043)

FIGURE 5. TIMING DIAGRAM FOR PROX/ALS EVENTS - NOT TO SCALE

ALS

ACTIVE

100ms

100ms

100ms

PROX

SENSOR

ACTIVE

IRDR

(CURRENT

DRIVER)

ALS CONVERSION TIME =

100ms (FIXED)

0.54ms FOR PROX

CONVERSION

SERIES OF

CURRENT PULSES

TOTALING 0.1ms

SLEEP TIME

(PROX_SLP)

100ms

100ms

SEVERAL µs BETWEEN

CONVERSIONS

TIME

TIME

TIME