ISL29034 Datasheet, PDF (11/14 Pages) Intersil Corporation – Wide dynamic range1

ISL29034
RESERVED BITS [B2:B0] AND [B6]
All RESERVED bits on the ISL29034 are Intersil used bits only.
Bit0 to Bit2 and Bit6 are RESERVED bits where their value might
change without any notification to the user. It is advised when
using the identification bits to identify the device in a syste, the
software should mask the Bit0 to Bit2 and Bit6 to Bit7 to properly
identify the device.
DEVICE ID BITS [B5:B3]
The ISL29034 provides 3 bits to identify the device in a system.
These bits are located on register address 0x0F, Bit3 to Bit5. The
identification bit value for the ISL29034 is xx101xxx. The device
identification bits are read only bits. It is important to notice that
Bit7 is a status bit for Brownout Condition (BOUT).
BROWNOUT STATUS BIT TO BOUT [B7]
Bit7 on register address 0x0F is a status bit for Brownout
Condition (BOUT). The default value of this bit is “BOUT = 1”
during the initial power-up, which indicates the device may
possibly have gone through a brownout condition. Therefore, the
status bit should be reset to “BOUT = 0” by an I²C write command
during the initial configuration of the device.
The default register value is 0xA8 at power-on.
Applications Information
Figure 15 is a normalized spectral response of various types of
light sources for reference.
1.0
0.9
FLUORESCENT
0.8
0.7
0.6
0.5
HALOGEN _INCAND.
0.4
SUN
0.3
0.2
0.1
0
350
550
750
950
WAVELENGTH (nm)
FIGURE 15. NORMALIZED SPECTRAL RESPONSE OF LIGHT SOURCES
Calculating Lux
The ISL29034’s ADC output codes, DATA, are directly
proportional to Lux in the ambient light sensing.
E_cal =   DATA
(EQ. 1)
Where E_cal is the calculated Lux reading. The constant  is
determined by the full-scale range and the ADC’s maximum
output counts. The constant is independent of the light sources
(fluorescent, incandescent and sunlight) because the light
sources IR component is removed during the light signal process.
The constant can also be viewed as the sensitivity (the smallest
Lux measurement the device can measure).
 = -_C----^Ro----_u-^a---_n-ⁿ---_t-^g-_m--^e--_a----_x-
(EQ. 2)
Where, Range is defined in Table 7 on page 10. Count_max is the
maximum output counts from the ADC.
The transfer function used for n-bits ADC becomes:
E_cal = ^R-----^a--₂--ⁿ--_n--^g----^e-  DATA
(EQ. 3)
Where n = 4, 8, 12 or 16. This is the number of ADC bits
programmed in the command register. 2ⁿ represents the
maximum number of counts possible from the ADC output. Data is
the ADC output stored in the data registers (02 hex and 03 hex).
Enhancing EV Accuracy
The device has on-chip passive optical filter designed to block
(reject) most of the incident Infra Red. However, EV
measurement may be vary under differing IR-content light
sources. In order to optimize the measurement variation
between differing IR-content light sources, ISL29034 provides IR
channel, which is programmed at COMMAND-1 (Reg0x0) to
measure the IR level of differing IR-content light sources.
The ISL29034’s ADC output codes, DATA, are directly
proportional to the IR intensity received in the IR sensing.
DATA_IR =   E_IR
(EQ. 4)
Then EV accuracy can be found in Equation 5:
EV_Accuracy = KxDATA_EV +   DATA_IR
(EQ. 5)
Here, DATA_EV is the received ambient light intensity ADC output
codes. K is a resolution of visible portion. Its unit is Lux/count.
The typical value of K is 0.82. DATA_IR is the received IR intensity.
The constant  changes with the spectrum of background IR,
such as A, F2 and D65 (Notes 8, 9 and 10). The also changes
with the ADC’s range and resolution selections. A typical for
Range1 and Range2 is -11292.86 and Range3 and Range4 is
2137.14 without IR tinted glass.
Noise Rejection
Electrical AC power worldwide is distributed at either 50Hz or
60Hz. Artificial light sources vary in intensity at the AC power
frequencies. The undesired interference frequencies are infused
on the electrical signals. This variation is one of the main sources
of noise for the light sensors. Integrating type ADC’s have
excellent noise-rejection characteristics for periodic noise
sources whose frequency is an integer multiple of the conversion
rate. By setting the sensor’s integration time to an integer
multiple of periodic noise signal, the performance of an ambient
light sensor can be improved greatly in the presence of noise. In
order to reject the AC noise, the integration time of the sensor
must to adjusted to match the AC noise cycle. For instance, 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.
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FN8370.2
August 19, 2016