ISL29021_14 Datasheet, PDF (7/12 Pages) Intersil Corporation – Digital Proximity Sensor with Interrupt Function

ISL29021
.
TABLE 7. CURRENT SOURCE CAPABILITY AT IRDR PIN
BITS 5 TO 4
IRDR PIN SOURCE CURRENT
00
12.5mA IR LED driver
01
25mA IR LED driver
10
50mA IR LED driver
11
100mA IR LED driver
4. Resolution: Bits 3 and 2. Bits 3 and 2 determine the ADC’s
resolution and the number of clock cycles per conversion
in Internal Timing Mode. 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 the device’s analog-to-digital (A/D) converter
samples the photodiode current signal for a measurement.
.
TABLE 8. RESOLUTION/WIDTH
BITS 3 TO 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
5. Range: Bits 1 and 0. The Full Scale Range (FSR) can be
adjusted via I²C using Bits 1 and 0. Table 9 lists the
possible values of FSR for the 499kΩ R_EXT resistor.
TABLE 9. RANGE/FSR
BITS 1:0 k
RANGE(k)
FSR @ IR SENSING
00
1
Range1
Refer to page 3
01
2
Range2
Refer to page 3
10
3
Range3
Refer to page 3
11
4
Range4
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 10. 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
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. 04 hex is the LSB and 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. 06 hex is the LSB and 07
hex is the MSB. By default, the Interrupt threshold HI is FF
hex for both LSB and MSB.
Integration and Conversion Time
The ADC resolution and f_OSC determines the integration
time, t_int.
t_int
=
2ⁿ
×
------¹-------
f_OSC
=
2ⁿ
×
----------------^R-----^E---^X----^T-----------------
725kHz × 499kΩ
(EQ. 1)
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 11. INTEGRATION TIME OF n-BIT ADC
R_EXT
(kΩ)
n = 16-BIT n = 12-BIT
n = 8-BIT
n = 4-BIT
250
45ms
2.812ms
175.5µs
10.8µs
499**
90ms
5.63ms
351µs
21.6µs
**Recommended R_EXT resistor value
External Scaling Resistor R_EXT for f_OSC and
Range
The ISL29021 uses an external resistor R_EXT to fix its
internal oscillator frequency, f_OSC. Range. f_OSC and Range
are inversely proportional to R_EXT. For user simplicity, the
proportionality constant is referenced to 499kΩ:
Range
=
-⁴---⁹---⁹----^k---^Ω---
R_EXT
×
R
a
n
ge
(
k
)
(EQ. 2)
f_OSC
=
4_----9_---9_----k_---Ω_---
R_EXT
×
725
k
H
z
(EQ. 3)
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...k_i) is zero. Similarly, setting the
device’s integration time to be an integer multiple of the
periodic noise signal, greatly improves the proximity sensor
output signal in the presence of noise.
ADC Output in IR Sensing
The ISL29021’s ADC output codes, DATA, are directly
proportional to the IR intensity received in the IR sensing.
DATA_IR = β × E_IR
(EQ. 4)
Here, E_IR is the received IR intensity. The constant β
changes with the spectrum of background IR noise like
sunlight and incandescent light. The β also changes with the
ADC’s range and resolution selections.
ADC Output in Proximity Sensing
In the proximity sensing, the ADC output codes, DATA, are
directly proportional to the total IR intensity from the
7
FN6732.0
March 3, 2009