ISL29018IROZ-T7 Intersil, ISL29018IROZ-T7 Datasheet - Page 9

• Manufacturer Part Number: ISL29018IROZ-T7
• Description: IC SENSOR AMB LGT-DTGL I2C 8ODFN
• Manufacturer: Intersil

Specifications of ISL29018IROZ-T7

• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

viewed as the sensitivity: the smallest lux measurement the
device can measure as shown in Equation 2.
α
Here, Range(k) is defined in Table 9. Count
maximum output counts from the ADC.
The transfer function used for n-bit ADC becomes
Equation 3:
Here, n = 4, 8, 12 or 16. This is the number of ADC bits
programmed in the command register. 2
maximum number of counts possible from the ADC output.
Data is the ADC output stored in the data registers (02 hex
and 03 hex).
Integration and Conversion Time
The ADC resolution and f
time, t
t
where n is the number of bits of resolution and n = 4, 8, 12 or
16. 2
programmed at the command register 01(hex) bits 3 and 2.
External Scaling Resistor R
Range
The ISL29018 uses an external resistor R
internal oscillator frequency, f
range, Range. f
R
referenced to 499kΩ as shown in Equations 5 and 6:
Noise Rejection
In general, integrating type 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 unwanted signal’s sum from
0ms to k*16.66ms (k = 1,2...k
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.
E
Range
f
**Recommended R
int
OSC
cal
EXT
R
499**
=
(kΩ)
250
EXT
=
----------------------------
Count
Range k ( )
=
n
. For user simplicity, the proportionality constant is
2
, therefore, is the number of clock cycles. n can be
=
int
n
Range k ( )
---------------------------
=
499kΩ
----------------- -
TABLE 11. INTEGRATION TIME OF n-BIT ADC
×
R
as shown in Equation 4.
499kΩ
----------------- -
------------- -
f
EXT
max
R
n = 16-BIT
2
OSC
n
1
EXT
(ms)
45
90
×
OSC
=
725
×
×
EXT
2
Range k ( )
DATA
n
kHz
and Range are inversely proportional to
×
resistor value
--------------------------------------------- -
725kHz
n = 12-BIT
OSC
2.812
(ms)
5.63
R
EXT
OSC
i
) is zero. Similarly, setting the
9
×
determines the integration
499kΩ
EXT
and the light sensing
n = 8-BIT
for f
175.5
(µs)
351
n
EXT
represents the
OSC
max
to fix its
is the
and
n = 4-BIT
10.8
21.6
(µs)
(EQ. 3)
(EQ. 5)
(EQ. 6)
(EQ. 2)
(EQ. 4)
ISL29018
ADC Output in IR Sensing
The ISL29018’s ADC output codes, DATA, are directly
proportional to the IR intensity received in the IR sensing.
Here, E
changes with the spectrum of background IR noise like
sunlight and incandescent light. The β also changes with the
ADC’s range and resolution selections.
ADC Output in Proximity Sensing
In the proximity sensing, the ADC output codes, DATA, are
directly proportional to the total IR intensity from the
background IR noise and from the IR LED driven by the
ISL29018.
Here, β and E
The constant γ depends on the spectrum of the used IR LED
and the ADC’s range and resolution selections. E
IR intensity which is emitted from the IR LED and reflected
by a specific objector to the ISL29018. E
current to the IR LED and the surface of the object. E
decreases with the square of the distance between the
object and the sensor.
If background IR noise is small, E
the ADC output directly decreases with the distance. If there
is significant background IR noise, ISL29018 offers two
schemes to reduce the effect. The first way is do a proximity
sensing using Scheme 0, immediately followed by an IR
sensing. The differential reading of ADC outputs from the
proximity and IR sensing will then reduce the effect of
background IR noise and directly decrease with the distance
between the object and the sensor. The second way is to do
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 12 for ADC output versus distance using
Scheme 0 detection.
Figure 9 shows ISL29018 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 10 shows ISL29018 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.
ISL29018 Proximity sensing relies on the amount of IR
reflected back from the objects to be detected. Clearly, it can
DATA
DATA
IR
PROX
IR
=
is the received IR intensity. The constant β
β
=
×
IR
E
β
IR
×
have the same meanings as in Equation 7.
E
IR
+
γ
×
E
LED
IR
can be neglected, and
LED
depends on the
February 11, 2010
LED
LED
FN6619.1
(EQ. 7)
(EQ. 8)
is the