ISL29033IROZ-T7 Datasheet, PDF (10/15 Pages) Intersil Corporation – Ultra-Low Lux, Low Power, Integrated Digital Ambient Light Sensor with Interrupt Function

ISL29033
R_EXT
(kΩ)
499
1000
TABLE 8. INTEGRATION TIME OF n-BIT ADC
n = 16-BIT
(ms)
n = 12-BIT
(ms)
n = 8-BIT
(µs)
n = 4-BIT
(µs)
100
6.25
391
24
200
12.5
782
48
External Scaling Resistor R_EXT for f_OSC and
Range
The ISL29033 uses an external resistor, R_EXT, to fix its internal
oscillator frequency, f_OSC, and the light sensing range, Range.
The f_OSC and Range are inversely proportional to R_EXT. For ease
of use, the proportionality constant is referenced to 499kΩ.
Calculation for Range is shown in Equation 5 and for f_OSC in
Equation 6.
Range = -⁴---⁹----⁹---^k----^Ω--- × Range(k)
R_EXT
(EQ. 5)
Typical Circuit
A typical application for the ISL29033 is shown in Figure 5. The
ISL29033 I²C address is internally hardwired as 1000100. The
device can be tied onto a system’s I²C bus together with other
I²C compliant devices.
Soldering Considerations
Convection heating is recommended for reflow soldering;
direct-infrared heating is not recommended. The plastic ODFN
package does not require a custom reflow soldering profile; it is
qualified to +260°C. A standard reflow soldering profile with a
+260°C maximum is recommended.
ALS Sensor Window Layout
Special care should be taken to ensure that the sensor, as shown
in the sensor location outline (Figure 6), is uniformly illuminated.
Shadows from off-angle window openings can affect uniform
illumination, which in turn can affect measurement results.
f_OSC
=
4_----9_----9_---k_----Ω_{--- × 655kHz}
R_EXT
(EQ. 6)
Noise Rejection
In general, integrating-type ADCs have excellent noise rejection
characteristics for periodic noise sources for which frequency is
an integer multiple of the conversion rate. For example, a 60Hz
AC unwanted signal’s sum from 0ms to k*16.66ms (k = 1,2...k_i)
is zero. 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.
ADC Output in IR Sensing
The ISL29033 ADC output codes, DATA, are directly proportional
to the IR intensity received in IR sensing, as shown in Equation 7.
DATA_IR = β × E_IR
(EQ. 7)
In this equation, E_IR is the received IR intensity. The constant, b,
changes with the spectrum of background IR noise, such as
sunlight and incandescent light. The constant, b, also changes
with ADC range and resolution selections.
Suggested PCB Footprint
It is important that users check Tech Brief 477, “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 ISL29033 is relatively insensitive to layout. Like other I²C
devices, it is intended to provide excellent performance even in
significantly noisy environments. Attention to a few
considerations will ensure best performance.
Route the supply and I²C traces as far as possible from all
sources of noise. Use two power-supply decoupling capacitors,
1µF and 0.1µF, placed close to the device.
10
FN7656.2
February 25, 2013