ISL29030A

9

FN7722.1

March 31, 2011

Principles of Operation

as 0b1000100.

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 seven 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 ISL29030A contains two photodiode arrays that convert

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

mimic the human eye wavelength response curve to visible light

(see Figure 7). The ALS photodiode 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 that operates in a similar

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

a user-supplied infrared LED, the emitted IR reflects off an object

(i.e., a human head) back into the ISL29030A, 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 ISL29030A 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

Registers PROX_DATA (wait 0.54ms) or ALSIR_DT1/2 (wait

100ms). The timing between ALS and Prox conversions is

arbitrary, as shown in Figure 3. 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]).

Ambient Light and IR Sensing

The ISL29030A is set for ambient light sensing when Register bit

ALSIR_MODE = 0 and ALR_EN = 1. The light-wavelength response of

the ALS appears as shown in Figure 6. ALS measuring mode (as

opposed to IR measuring mode) is set by default.

When the part is programmed for infrared (IR) sensing

(ALSIR_MODE = 1; ALS_EN = 1), infrared light is converted into a

current and is digitized by the same ALS ADC. The result of an IR

conversion is strongly related to the amount of IR energy incident

on the sensor, but it is unitless and is referred to in digital counts.

Proximity Sensing

When proximity sensing is enabled (PROX_EN = 1), the external

IR LED is driven through the IRDR pin for 0.1ms by the built-in IR

LED driver. The amplitude of the IR LED current depends on

Register 1 bit 3: PROX_DR. If this bit is low, the load sees a fixed

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

FIGURE 3. TIMING DIAGRAM FOR PROX/ALS EVENTS - NOT TO SCALE