ISL76683 Datasheet, PDF (10/17 Pages) Intersil Corporation – Light-to-Digital Output Sensor with Gain Selection, Interrupt Function

ISL76683
2. Range/Gain; Bits 3 and 2. The Full Scale Range can be
adjusted
adjusted
vbiyaaI^{2nCeuxtseinrngatlhreesGiastionr/RRaEX}n^Tgeanfudn/cotrioitnc. ^{aGnaibne/Range}
has four possible values, Range(k) where k is 1 through 4.
Table 9 lists the possible values of Range(k) and the resulting
FSR for some typical value R_EXT resistors.
TABLE 9. RANGE/GAIN TYPICAL FSR LUX RANGES
BITS
RANGE
3:2 k (k)
0:0 1 973
FSR LUX
RANGE@
R_EXT = 100k
973
FSR LUX
RANGE@
R_EXT = 50k
1946
FSR LUX
RANGE@
R_EXT = 500k
195
0:1 2 3892
3892
7784
778
1:0 3 15,568
15,568
31,136
3114
1:1 4 62,272
62,272
124,544
12,454
3. Interrupt persist; Bits 1 and 0. The interrupt pin and the
interrupt flag is triggered/set when the data sensor reading is
out of the interrupt threshold window after m consecutive
number of integration cycles. The interrupt persist bits
determine m.
TABLE 10. INTERRUPT PERSIST
BITS 1:0
NUMBER OF INTEGRATION CYCLES
0:0
1
0:1
4
1:0
8
1:1
16
Interrupt Threshold HI Register 02(hex)
This register sets the HI threshold for the interrupt pin and the
interrupt flag. By default, the Interrupt threshold HI is FF(hex).
The 8-bit data written to the register represents the upper MSB of
a 16-bit value. The LSB is always 00(hex).
Interrupt Threshold LO Register 03(hex)
This register sets the LO threshold for the interrupt pin and the
interrupt flag. By default, the Interrupt threshold LO is 00(hex).
The 8-bit data written to the register represents the upper MSB of
a 16-bit value. The LSB is always 00(hex).
Sensor Data Register 04(hex) and 05(hex)
When the device is configured to output a 16-bit data, the least
significant byte is accessed at 04(hex), and the most significant
byte can be accessed at 05(hex). The sensor data register is
refreshed after every integration cycle.
Timer Data Register 06(hex) and 07(hex)
Note that the timer counter value is only available when using the
External Timing Mode. The 06(hex) and 07(hex) are the LSB and
MSB respectively of a 16-bit timer counter value corresponding to
the most recent sensor reading. Each clock cycle increments the
counter. At the end of each integration period, the value of this
counter is made available over the I²C. This value can be used to
eliminate noise introduced by slight timing errors caused by
imprecise external timing. Microcontrollers, for example, often
cannot provide high-accuracy command-to-command timing,
and the timer counter value can be used to eliminate the
resulting noise.
TABLE 11. DATA REGISTERS
ADDRESS
(hex)
CONTENTS
04 Least-significant byte of most recent sensor reading.
05 Most-significant byte of most recent sensor reading.
06 Least-significant byte of timer counter value corresponding to
most recent sensor reading.
07
Most-significant byte of timer counter value corresponding to
most recent sensor reading.
Calculating Lux
The ISL76683’s output codes, DATA, are directly proportional to lux.
E = α × DATA
(EQ. 1)
The proportionality constant α is determined by the Full Scale
Range, FSR, and the n-bit ADC, which is user defined in the
command register. The proportionality constant can also be
viewed as the resolution; The smallest lux measurement the
device can measure is α.
α = ^F----^S----^R--
2ⁿ
(EQ. 2)
Full Scale Range, FSR, is determined by the software
programmable Range/Gain, Range(k), in the command register
and an external scaling resistor R_EXT which is referenced to
100kΩ.
FSR
=
R
an
ge
(k)
×
1_----0_----0_----k_---Ω_---
R_EXT
(EQ. 3)
The transfer function effectively for each timing mode becomes:
INTERNAL TIMING MODE
Range(k) × ¹----⁰---⁰-----^k---^Ω---
E = -------------------------------------^R----^E---^X----^T---- × DATA
2ⁿ
(EQ. 4)
EXTERNAL TIMING MODE
Range(k) × ¹----⁰---⁰-----^k---^Ω---
E = -------------------------------------^R----^E---^X----^T---- × DATA
COUNTER
(EQ. 5)
n = 4, 8, 12, or 16. This is the number of clock cycles
programmed in the command register.
Range(k) is the user defined range in the Gain/Range bit in the
command register.
R_EXT is an external scaling resistor hardwired to the R_EXT pin.
DATA is the output sensor reading in number of counts available
at the data register.
2ⁿ represents the maximum number of counts possible in
Internal Timing Mode. For the External Timing Mode, the
maximum number of counts is stored in the data register named
COUNTER.
COUNTER is the number increments accrued for between
integration time for External Timing Mode.
10
FN7697.1
January 31, 2011