NOA3302 Datasheet, PDF (19/23 Pages) ON Semiconductor – Digital Proximity Sensor

NOA3302
Proximity Sensor Operation
NOA3302 operation is divided into three phases: power
up, configuration and operation. On power up the device
initiates a reset which initializes the configuration registers
to their default values and puts the device in the standby
state. At any time, the host system may initiate a software
reset by writing 0x01 to register 0x01. A software reset
performs the same function as a power-on-reset.
The configuration phase may be skipped if the default
register values are acceptable, but typically it is desirable to
change some or all of the configuration register values.
Configuration is accomplished by writing the desired
configuration values to registers 0x02 through 0x17.
Writing to configuration registers can be done with either
individual I²C byte-write commands or with one or more
I²C block write commands. Block write commands specify
the first register address and then write multiple bytes of data
in sequence. The NOA3302 automatically increments the
register address as it acknowledges each byte transfer.
Proximity sensor measurement is initiated by writing
appropriate values to the CONTROL register (0x17).
Sending an I2C_STOP sequence at the end of the write
signals the internal state machines to wake up and begin the
next measurement cycle. Figures 23 and 24 illustrate the
activity of key signals during a proximity sensor
measurement cycle. The cycle begins by starting the
precision oscillator and powering up and calibrating the
proximity sensor receiver. Next, the IR LED current is
modulated according to the LED current setting at the
chosen LED frequency and the values during both the on and
off times of the LED are stored (illuminated and ambient
values). Finally, the proximity reading is calculated by
subtracting the ambient value from the illuminated value
and storing the result in the 16 bit PS_Data register. In
One-shot mode, the PS receiver is then powered down and
the oscillator is stopped (unless there is an active ALS
measurement). If Repeat mode is set, the PS receiver is
powered down for the specified interval and the process is
repeated. With default configuration values (receiver
integration time = 300 ms), the total measurement cycle will
be less than 2 ms.
I2C Stop
PS Power
4MHz Osc On
LED Burst
Integration
Data Available
50−200 ms
9ms
~600 ms
0−100 ms
8 clks 12 ms
Integration Time
100−150 ms
Figure 23. Proximity Sensor One−Shot Timing
I2C Stop
PS Power
4MHz Osc On
50−200 ms
LED Burst
Integration
Data Available
Interval
~600 ms
9ms
0−100 ms
8 clks 12 ms
Integration Time
100−150 ms
Figure 24. Proximity Sensor Repeat Timing
(Repeat)
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