ISL29021_14 Datasheet, PDF (4/12 Pages) Intersil Corporation – Digital Proximity Sensor with Interrupt Function

ISL29021
Electrical Specifications V_{SUP(VDDD,VDDA)} = 3V, T_A = +25°C, R_EXT = 499kΩ 1% tolerance, 16-bit ADC operation, unless otherwise
specified. (Continued)
PARAMETER
DESCRIPTION
CONDITION
MIN TYP MAX UNIT
I_{SUP (IRLED1)} Supply Current of Proximity Sensing
I_{SUP (IRLED2)} Supply Current of Proximity Sensing
Duty Cycle Duty Cycle of IR LED Modulation
IS<1:0> = 0, Freq = 0 (Note 4)
IS<1:0> = 0, Freq = 1 (Note 4)
101
mA
51
mA
50
%
PROX-IR Differential ADC Output of IR and Proximity IR and proximity sensing with Range 2; 15Ω @ IRDR
1.0
%
PROX
Sensing With Object Far Away to Provide pin, IS<1:0> = 0, Freq = 0; E = 210 lux, Sunlight.
No Reflection
NOTES:
2. V_SUP is the common voltage to V_DDD and V_DDA.
3. 850nm infrared LED is used in production test. The 850nm LED irradiance is calibrated to produce the same DATA_IR count against an illuminance
level of 210 lux sunlight at sea level.
4. See “Register Set” on page 6.
Principles of Operation
Photodiodes and ADC
The ISL29021 contains a photodiode array which converts
infrared energy into current. The spectral response for IR
sensing is shown in Figure 6 in the performance curves section.
After IR radiation is converted to current during the infrared
signal processing, the current output is converted to digital by a
built-in 16-bit Analog-to-Digital Converter (ADC). An I²C
command reads the infrared light intensity in counts.
The converter is a charge-balancing integration type 16-bit
ADC. The chosen method for conversion is best for converting
small current signals in the presence of an AC periodic noise. A
100ms integration time, for instance, highly rejects 50Hz and
60Hz power line noise simultaneously. See “Integration and
Conversion Time” on page 7.
The built-in ADC offers user flexibility in integration time or
conversion time. Integration time is determined by an internal
oscillator (f_OSC), and the n-bit (n = 4, 8, 12,16) counter inside
the ADC. A good balancing act of integration time and
resolution depending on the application is required for optimal
results.
The ADC has I²C programmable range select to dynamically
accommodate various IR conditions. For very dim
conditions, the ADC can be configured at its lowest range
(Range 1). For very bright conditions, the ADC can be
configured at its highest range (Range 4) in the proximity
sensing.
Low-Power Operation
The ISL29021 initial operation is at the power-down mode
after a supply voltage is provided. The data registers contain
the default value of 0. When the ISL29021 receives an I²C
command to do a one-time measurement from an I²C master,
it will start ADC conversion with proximity sensing. It will go to
the power-down mode automatically after one conversion is
finished and keep the conversion data available for the master
to fetch anytime afterwards. The ISL29021 will continuously
do ADC conversion with proximity sensing if it receives an I²C
command of continuous measurement. It will continuously
update the data registers with the latest conversion data. It will
go to the power-down mode after it receives the I²C command
of power-down.
Infrared and Proximity Sensing
There are four operational modes in ISL29021: programmable
IR sensing once with auto power-down, programmable
proximity sensing once with auto power-down, programmable
continuous IR sensing and programmable continuous
proximity sensing. These four modes can be programmed in
series to fulfill the application needs. The detailed program
configuration is listed in “Register Set” on page 6.
When the part is programmed for infrared (IR) sensing, the
IR light with wavelength within the “IR or Proximity Sensing”
spectral response curve on Figure 6 is converted into
current. With ADC, the current is converted to an unsigned
n-bit (up to 16 bits) digital output.
When the part is programmed for proximity sensing, the
external IR LED is turned on by the built-in IR LED driver
through the IRDR pin. The amplitude of the IR LED current
and the IR LED modulation frequency can be programmed
through Command Register II. When the IR from the LED
reaches an object and gets reflected back, the reflected IR
light with wavelength within the “IR or Proximity Sensing”
spectral response curve in Figure 6 is converted into current.
With ADC, the current is converted to an unsigned n-bit (up
to 16 bits) digital output. The output reading is inversely
proportional to the square of the distance between the
sensor and the object.
Interrupt Function
The active low interrupt pin is an open drain pull-down
configuration. There is also an interrupt bit in the I²C register.
The interrupt serves as an alarm or monitoring function to
determine whether the infrared light level or the proximity
detection level exceeds the upper threshold or goes below the
lower threshold. The user can also configure the persistency
4
FN6732.0
March 3, 2009