ISL29015 データシートの表示（PDF） - Renesas Electronics
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ISL29015 Datasheet PDF : 13 Pages
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ISL29015
ISL29015
device’s analog-to-digital (A/D) converter samples the
photodiode current signal for a measurement.
.
TABLE 5. RESOLUTION/WIDTH
BITS 3:2
00
01
10
11
NUMBER OF CLOCK CYCLES
216 = 65,536
212 = 4,096
28 = 256
24 = 16
n-BIT ADC
16
12
8
4
4. Range: Bits 1 and 0. The Full Scale Range (FSR) can be
adjusted via I2C using Bits 1 and 0. Table 6 lists the possible
values of FSR for the 499kREXT resistor.
TABLE 6. RANGE/FSR LUX
BITS
1:0 k RANGE(k)
FSR (LUX) @
ALS SENSING
FSR @ IR
SENSING
00 1
Range1
1,000
Refer to page 3
01 2
Range2
4,000
Refer to page 3
10 3
Range3
16,000
Refer to page 3
11 4
Range4
64,000
Refer to page 3
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 ADC. 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.
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
Calculating Lux
The ISL29015’s ADC output codes, DATA, are directly
proportional to lux in the ambient light sensing.
Ecal = DATA
(EQ. 1)
Here, Ecal 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 on the light
sources (fluorescent, incandescent and sunlight) because of
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 is shown in Equation 2.
= C-R----o-a---u-n---ng----te--m----ak----x-
(EQ. 2)
Here, Range(k) is defined in Table 6. Countmax is the
maximum output counts from the ADC.
The transfer function used for n-bit ADC becomes:
Ecal = R-----a----n--2--g--n--e------k---- DATA
(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).
Integration and Conversion Time
The ADC resolution and fOSC determines the integration time,
tint.
tint = 2n -f-O----1-S----C-- = 2n 7----2---5----k---H--R---z--E---X----T-4---9---9----k------
(EQ. 4)
where n is the number of bits of resolution and n = 4, 8, 12 or
16. 2n, therefore, is the number of clock cycles. n can be
programmed at the command register 01(hex) bits 3 and 2.
TABLE 8. INTEGRATION TIME OF n-BIT ADC
REXT
(k
250
n = 16-BIT
45ms
n = 12-BIT
2.812ms
n = 8-BIT
175.5µs
n = 4-BIT
10.8µs
499**
90ms
5.63ms
351µs
21.6µs
**Recommended REXT resistor value
External Scaling Resistor REXT for fOSC and Range
The ISL29015 uses an external resistor REXT to fix its internal
oscillator frequency, fOSC and the light sensing range. fOSC
and Range are inversely proportional to REXT. For user
simplicity, the proportionality constant is referenced to 499k:
Range = -4-R--9---E9----Xk---T--- Rangek
(EQ. 5)
fOSC = 4--R--9---E9----Xk---T--- 725kHz
(EQ. 6)
Noise Rejection
In general, integrating type ADC’s have excellent noise-rejection
characteristics for periodic noise sources whose frequency is an
integer multiple of the conversion rate. For instance, a 60Hz AC
unwanted signal’s sum from 0ms to k*16.66ms (k = 1,2...ki) 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 ISL29015’s ADC output codes, DATA, are directly
proportional to the IR intensity received in the IR sensing
phase.
DATAIR = EIR
(EQ. 7)
FN6522 Rev 0.00
October 31, 2008
Page 7 of 13
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