ISL29030

11

FN6872.1

November 12, 2012

independent light sensor which can instruct a system to “wake

up” or “go to sleep.”

An ALS interrupt event (ALS_FLAG) is governed by Registers 5 through

7. The user writes a high and low threshold value to these registers

and the ISL29030 will issue an ALS interrupt flag if the actual count

stored in Registers 0x9 and 0xA are outside the user’s programmed

window. The user must write 0 to clear the ALS_FLAG.

A proximity interrupt event (PROX_FLAG) is governed by the high

and low thresholds in registers 3 and 4 (PROX_LT and PROX_HT).

PROX_FLAG is set when the measured proximity data is more

than the higher threshold X-times-in-a-row (X is set by user; see

following paragraph). The proximity interrupt flag is cleared when

the prox data is lower than the low proximity threshold

X-times-in-a-row, or when the user writes “0” to PROX_FLAG.

Interrupt persistency is another useful option available for both

ALS and proximity measurements. Persistency requires X-in-a-

row interrupt flags before the INT pin is driven low. Both ALS and

Prox have their own independent interrupt persistency options.

See ALS_PRST and PROX_PRST bits in Register 2.

The final interrupt option is the ability to AND or OR the two

interrupt flags using Register 2 Bit 0 (INT_CTRL). If the user

wants both ALS/Prox interrupts to happen at the same time

before changing the state of the interrupt pin, set this bit high. If

the user wants the interrupt pin to change state when either the

ALS or the Proximity interrupt flag goes high, leave this bit to its

default of 0.

directly proportional to the digital count stored in register bits

ALSIRDATA[11:0]. When ALS_EN = 0, this pin is in a high

impedance state. See Figure 15 for the effects of the compliance

ALS Range 1 Considerations

When measuring ALS counts higher than 1800 on range 1

(ALSIR_MODE = 0, ALS_RANGE = 0, ALS_DATA > 1800), switch

to range 2 (change the ALS_RANGE bit from “0” to “1”) and

remeasure ALS counts. This recommendation pertains only to

applications where the light incident upon the sensor is IR-heavy

and is distorted by tinted glass that increases the ratio of infrared

to visible light. For more information, see the separate ALS

Range 1 Considerations document.

Considerations

After power-up, or if the user’s power supply temporarily deviates

from our specification (2.25V to 3.63V), Intersil recommends the

user write the following: write 0x00 to register 0x01, write 0x29 to

register 0x0F, write 0x00 to register 0x0E, and write 0x00 to register

0x0F. The user should then wait ~1ms or more and then rewrite all

registers to the desired values. If the user prefers a hardware reset

or more, power back up at the required slew rate, and write registers

to the desired values.

Power-Down

The power-down can be set 2 ways by the user. The first is to set both

PROX_EN and ALS_EN bits to 0 in Register 1. The second and more

simple way is to set all bits in Register 1 to 0 (0x00).

Calculating Lux

The ISL29030’s ADC output codes are directly proportional to lux

when in ALS mode (see ALSIR_MODE bit).

represents the ADC code. The constant

α to plug in is determined

by the range bit ALS_RANGE (register 0x1 bit 1) and is

independent of the light source type.

Table 15 shows two different scale factors: one for the low range

(ALS_RANGE = 0) and the other for the high range (ALS_RANGE

= 1).

Noise Rejection

Charge balancing ADC’s have excellent noise-rejection

characteristics for periodic noise sources whose frequency is an

integer multiple of the conversion rate. For instance, a 60Hz AC

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. Since wall sockets

may output at 60Hz or 50Hz, our integration time is 100ms: the

lowest common integer number of cycles for both frequencies.

Proximity Detection of Various Objects

Proximity sensing relies on the amount of IR reflected back from

objects. A perfectly black object would absorb all light and reflect

no photons. The ISL29030 is sensitive enough to detect black ESD

foam which reflects only 1% of IR. For biological objects, blonde

hair reflects more than brown hair and customers may notice that

skin tissue is much more reflective than hair. IR penetrates into

the skin and is reflected or scattered back from within. As a result,

the proximity count peaks at contact and monotonically decreases

as skin moves away. The reflective characteristics of skin are very

different from that of paper.

Typical Circuit

A typical application for the ISL29030 is shown in Figure 5. The

TABLE 15. ALS SENSITIVITY AT DIFFERENT RANGES

ALS_RANGE

(Lux/Count)

0

0.0326

1

0.522

×

=

(EQ. 2)