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FN6467.4

May 5, 2011

a proximity sensing using Scheme 1 to do on-chip

background IR noise subtraction. While Scheme 0 has wider

dynamic range, Scheme 1 proximity detection is faster but

with half the resolution. Please refer to “Typical Performance

Curves” on page 13 for ADC output versus distance using

Scheme 0 detection.

Figure 10 shows ISL29011 configured at 12-bit ADC

resolution and sensitivity range select at 16000 (range 3) for

the proximity reading. A 12.5mA external LED current at

360kHz modulation frequency detects three different sensing

objects: 92% brightness paper, 18% gray card and ESD

black foam. Figure 11 shows ISL29011 configured at 12-bit

ADC resolution and sensitivity range select at 1000

(range 1) for the proximity reading, with a programmed

external LED at 360kHz modulation frequency, detecting the

same sensing object: 18% gray card under four different

external LED current: 12.5mA, 25mA, 50mA and 100mA to

compare the proximity readout versus distance.

ISL29011 Proximity sensing relies on the amount of IR

reflected back from the objects to be detected. Clearly, it can

not detect an optically black object that reflects no light.

However, ISL29011 is sensitive enough to detect a black ESD

foam, which reflects slightly less than 1% of IR, as shown in

Figure 10 on page 13. For biological objects, blonde hair

reflects more than brunette hair, as expected and shown in

Figure 12. Also 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. This characteristic is very different from that of a plain

paper reflector.

Interrupt Function

An interrupt event (FLAG) is governed by bit2 in

logic low(0), which means INT is cleared or not triggered yet.

Then ISL29011 will issue an ambient (ALS/IR) or proximity

interrupt flag if the actual count stored in Register 0x2 and

0x3 are outside the user's programmed window. The user

must read Register 0x0 to clear interrupt.

Interrupt persistency at bit1 and bit0 of COMMAND1 is

another useful option available for both ambient/IR and

proximity measurement. Persistency requires x-in-a-row

interrupt flags before the INT pin is driven low. Then, user

must read Register 0x0 to clear Interrupt.

Upon power-up, please ensure a VDD slew rate of 0.5V/ms

or greater. 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 0x00 to two registers:

0x08, 0x00 (in that order), wait ~1ms or more and then

rewrite all registers as desired.

LED Modulation for Proximity Detection

ISL29011 offers two ways to modulate the LED in the

Proximity Detection mode - DC or 360kHz (with 50% duty

cycle) by bit 6 of register 01h. At the IRDR pin, there are four

different IRDR LED currents; 12.5, 25, 50, and 100mA

outputs selectable by bits 4 and 5 of register 01h. With the

LED running in the DC mode, the proximity detection is twice

as sensitive but consumes 2 times more current. The

sensitivity of LED 50mA, DC 50mA is identical to that of

100mA, 360kHz modulation. Please note that the ISL29011

does not include a LED.

Current Consumption Estimation

The low power operation is achieved through sequential

readout in the serial fashion, as shown in Figure 4, the

device requires three different phases in serial during the

entire detection cycle to do ambient light sensing, infrared

sensing and proximity sensing. The external IR LED will only

be turned on during the proximity sensing phase under user

program controlled current at modulated frequency depends

on user selections. Figure 4 also shows the current

consumption during each ALS, IR sensing and Proximity

sensing phase. For example, at 8-bit ADC resolution the

integration time is 0.4ms. If user programed 50mA current to

supply external IR LED at 360kHz modulated frequency,

during the entire operation cycle that includes ALS, IR

sensing and Proximity sensing three different serial phases,

the detection occurs once every 30ms, the average current

consumption including external IR LED drive current can be

calculated from Equation 9:

If at a 12-bit ADC resolution where the integration time for

each serial phase becomes 7ms and the total detection time

becomes 100ms, the average current can be calculated from

Equation 10:

Suggested PCB Footprint

It is important that the users check the “Surface Mount

Assembly Guidelines for Optical Dual FlatPack No Lead

(ODFN) Package” before starting ODFN product board

mounting.

http://www.intersil.com/data/tb/TB477.pdf

Layout Considerations

The ISL29011 is relatively insensitive to layout. Like other

even in significantly noisy environments. There are only a

few considerations that will ensure best performance.

sources of noise. Use two power-supply decoupling

capacitors 1µF and 0.1µF and place them close to the VDDA

and VDDD pins of the device.

++

+

()

[]/30ms = 0.35mA

(EQ. 9)

++

+

()

[]/100ms = 1.83mA

(EQ. 10)

ISL29011