ISL29021 Ver la hoja de datos (PDF) - Renesas Electronics
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ISL29021 Datasheet PDF : 12 Pages
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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 499kREXT 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 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. 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
REXT
(k
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 REXT resistor value
External Scaling Resistor REXT for fOSC and Range
The ISL29021 uses an external resistor REXT to fix its internal
oscillator frequency, fOSC. 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. 2)
fOSC = 4--R--9---E9----Xk---T--- 725kHz
(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...ki) 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.
DATAIR = EIR
(EQ. 4)
Here, EIR is the received IR intensity. The constant changes
with the spectrum of background IR noise like sunlight and
incandescent light. The 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
FN6732 Rev 0.00
March 3, 2009
Page 7 of 12
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