ISL29033
9
FN7656.5
September 28, 2016
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Command Register II 01 (Hex)
The second command register has the following functions:
1. Resolution: Bits 3 and 2. Bits 3 and 2 determine the ADC
resolution and the number of clock cycles per conversion
(Table 5
). Changing the number of clock cycles does more than
just change the resolution of the device; it also changes the
integration time, which is the period during which the
Analog-to-Digital (A/D) converter samples the photodiode
current signal for a measurement.
2. Range: Bits 1 and 0. The Full Scale Range (FSR) can be
adjusted through the I
2
C by using Bits 1 and 0. Table 6 lists
the possible values of FSR for the 499kΩ R
EXT
resistor.
Data Registers (02 Hex and 03 Hex)
The device has two 8-bit read-only registers to hold the data from
LSB to MSB for the ADC (Table 7
). The Most Significant Bit (MSB)
is accessed at 03 hex and the Least Significant Bit (LSB) is
accessed at 02 hex. For 16-bit resolution, the data is from D0 to
D15; for 12-bit resolution, the data is from D0 to D11; for 8-bit
resolution, the data is from D0 to D7. The registers are refreshed
after every conversion cycle.
Interrupt Registers (04, 05, 06, and 07 Hex)
Registers 04 and 05 hex set the Low (LO) threshold for the
interrupt pin and the interrupt flag. Register 04 hex is the LSB
and Register 05 hex is the MSB. By default, the interrupt
threshold LO is 00 hex for both LSB and MSB.
Registers 06 and 07 hex set the High (HI) threshold for the
interrupt pin and the interrupt flag. Register 06 hex is the LSB
and Register 07 hex is the MSB. By default, the interrupt
threshold HI is FF hex for both LSB and MSB.
Calculating Lux
The ISL29033 ADC output codes, DATA, are directly proportional
to lux in ambient light sensing, as shown in Equation 1.
In this equation, E
cal
is the calculated lux reading. The constant,
α, is determined by the full scale range and the ADC maximum
output counts. The constant is independent of the light sources
(fluorescent, incandescent, and sunlight) because the light
source 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), as shown in
Equation 2
.
In this equation, Range(k) is as defined in Table 6
. Count
max
is
the maximum output counts from the ADC.
The transfer function used for n-bits ADC is as shown in
Equation 3
:
In this equation, n = 4, 8, 12 or 16 and is the number of ADC bits
programmed in the command register. The number 2
n
represents the maximum number of counts possible from the
ADC output. Data is the ADC output stored in data
Registers 02 hex and 03 hex.
Integration and Conversion Time
ADC resolution and f
OSC
determine the integration time, t
int
, as
shown in Equation 4
.
In this equation, n is the number of bits of resolution and n = 4, 8,
12 or 16. Therefore, 2
n
is the number of clock cycles. The value
of n can be programmed at the command register, Register 01
hex, Bits 3 and 2 see (Table 8
).
TABLE 4. INTERRUPT PERSIST
BIT 1:0 NUMBER OF INTEGRATION CYCLES
00 1
01 4
10 8
11 16
TABLE 5. ADC RESOLUTION DATA WIDTH
BITS 3:2 NUMBER OF CLOCK CYCLES n-BIT ADC
00 2
16
= 65,536 16
01 2
12
= 4,096 12
10 2
8
= 256 8
11 2
4
= 16 4
TABLE 6. RANGE/FSR LUX
BITS 1:0 k RANGE(k) FSR (lux) AT ALS SENSING
00 1 Range1 125
01 2 Range2 500
10 3 Range3 2,000
11 4 Range4 8,000
TABLE 7. DATA REGISTERS
ADDRESS
(HEX) CONTENTS
02 D0 is LSB for 4-, 8-, 12- or 16-bit resolution; D3 is MSB for
4-bit resolution; D7 is MSB for 8-bit resolution
03 D15 is MSB for 16-bit resolution; D11 is MSB for 12-bit
resolution
TABLE 8. INTEGRATION TIME OF n-BIT ADC
R
EXT
(kΩ)
n = 16-BIT
(ms)
n = 12-BIT
(ms)
n = 8-BIT
(µs)
n = 4-BIT
(µs)
499 100 6.25 391 24
1000 200 12.5 782 48
Range k
Count
max
----------------------------
=
(EQ. 2)
(EQ. 3)
E
cal
Range k
2
n
---------------------------
DATA=
t
int
2
n
1
f
OSC
--------------
2
n
R
EXT
655kHz 499k
----------------------------------------------
==
(EQ. 4)
