ISL29035_14 Datasheet, PDF (12/16 Pages) Intersil Corporation – Integrated Digital Light Sensor with Interrupt

ISL29035
The lower interrupt threshold registers are used to set the lower
trigger point for interrupt generation. If the ALS value crosses
below or is equal to the lower threshold, an interrupt is asserted
on the interrupt pin and the interrupt status. Registers
INT_LT_LSB (0x04) and INT_LT_MSB (0x05) provide the low and
high bytes, respectively, of the lower interrupt threshold. The high
and low bytes from each set of registers are combined to form a
16-bit threshold value. The interrupt threshold registers default to
0x00 upon power-up.
Upper Interrupt Threshold Registers
(Address: 0x06 and 0x07)
TABLE 14. INTERRUPT REGISTER BITS
NAME
ADDR
REGISTER BITS
DFLT
(Hex) B7 B6 B5 B4 B3 B2 B1 B0 (Hex)
INT_HT_LSB 0x06 TH7 TH6 TH5 TH4 TH3 TH2 TH1 TH0 0xFF
INT_HT_MSB 0x07 TH15 TH14 TH13 TH12 TH11 TH10 TH9 TH8 0xFF
The upper interrupt threshold registers are used to set the upper
trigger point for interrupt generation. If the ALS value crosses
above or is equal to the upper threshold, an interrupt is asserted
on the interrupt pin and the interrupt status. Registers
INT_HT_LSB (0x06) and INT_HT_MSB (0x07) provide the low and
high bytes, respectively, of the upper interrupt threshold. The high
and low bytes from each set of registers are combined to form a
16-bit threshold value. The interrupt threshold registers default to
0xFF on power-up.
ID Register (Address: 0x0F)
TABLE 15. ID REGISTER BITS
ADDR
NAME (Hex) B7
REGISTER BITS
B6 B5 B4 B3 B2 B1 B0
DFLT
ID 0x0F BOUT RESERVED 1 0 1 RESERVED 1x101xxx
The ID register has three different type of information.
RESERVED BITS (B0 - B2 AND B6)
All RESERVED bits on the ISL29035 are Intersil used bits only.
Bit0 - 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 system the
software should mask the Bit0 - Bit2 and Bit6 – Bit7 to properly
identify the device.
DEVICE ID BITS (B3 – B5)
The ISL29035 provides 3-bits to identify the device in a system.
These bits are located on register address 0x0F, Bit3 – Bit5. The
identification bit value for the ISL29035 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 - 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
The plot below is a normalized spectral response of various types
of light sources for reference.
1.0
0.9
0.8
0.7
0.6
0.5
0.4
0.3
0.2
0.1
0
350
FLUORESCENT
HALOGEN
SUN
INCAND.
550
750
950
WAVELENGTH (nm)
FIGURE 14. NORMALIZED SPECTRAL RESPONSE OF LIGHT SOURCES
Calculating Lux
The ISL29035’s ADC output codes, DATA, are directly
proportional to Lux in the ambient light sensing.
E_cal =   DATA
(EQ. 1)
Here, 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).

=
-----^R-----^a----ⁿ----^g---^e-------
Count_max
(EQ. 2)
Here, Range is defined in Table 8 on page 11. Count_max is the
maximum output counts from the ADC.
The transfer function used for n-bits ADC becomes:
E_cal
=
R_-----a_----n_----g_----e_-
2ⁿ

D
A
T
A
(EQ. 3)
Here, 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
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FN8371.1
November 12, 2014