PixArt Imaging Inc.
Track-on-Glass Laser Sensor
Eye Safety
The sensor and the associated components in the sche-
matic of Figure 6 are intended to comply with Class 1 Eye
Safety Requirements of IEC/EN 60825-1.
PixArt Imaging
calibrates the sensor’s laser output power (LOP) to
Class 1 eye safety level and store the registers values that
control the LOP prior shipping out, thus no LOP calibra-
tion is required in complete mouse system at manufac-
turer site.
The sensor is designed to maintain the laser output power
using the lens within Class 1 Eye Safety requirements over
components manufacturing tolerances under the recom-
mended operating conditions and application circuits of
Figure 6 as specified in this document. Under normal op-
erating conditions, the sensor generates the drive current
for the VCSEL. Increasing the LOP by other means on hard-
ware and software can result in a violation of the Class 1
eye safety limit of 716μW. For more information, please
refer to Eye Safety Application Note.
The following conditions are applied during LOP testing:
The system is operated at the typical recommended
operating supply voltage and temperature of 25°C ±
5°C.
The VDD3 value is no greater than 300mV above the
typical recommended operating conditions.
No allowance for optical power meter accuracy is
assumed.
Laser Power Adjustment Procedure
The
PixArt
pre-calibrated laser settings will always be
loaded automatically into the SPI Laser registers: LA-
SER_CTRL0, LASER_CTRL1, LP_CFG0 and LP_CFG1 upon
the SROM is successfully downloaded into the sensor. For
testing purpose, the pre-calibrated laser settings can be
overwritten by changing the SPI laser registers with new
laser setting after SROM download.
1.
2.
3.
4.
The ambient temperature should be 25°C ± 5°C.
Set VDD3 to the typical recommended operating
voltage.
Power up,reset the sensor and download SROM
Enable the Calibration mode by writing 010b to Bit-
[3, 2, 1] of LASER_CTRL0 register to set the laser to
continuous ON mode.
Set the Range bit (Bit-7) of LASER_CTRL0 register to 0.
Set the Range_C bit (Bit-7) of LASER_CTRL1
complement to setting of Range bit in LASER_CTRL0
register.
To turn on the laser, set the Forced_Disabled bit (Bit-0)
of LASER_CTRL0 register to 0 and set Bit-6 of LASER_
CTRL1 register to 1.
Set the laser current to the minimum value by writing
0x00 to LP_CFG0 register and the complementary
value 0xFF to LP_CFG1 register.
Program LP_CFG0 and LP_CFG1 registers with
increasing values to achieve an output power as close
to 506μW as possible without exceeding it for Eye
Safety Class 1 classification.
Laser Drive Mode
The laser is pulsed automatically during Run and Rest
modes. For testing purpose, the laser can be set to con-
tinuous ON mode for laser output power measurement.
The default setting of laser is in Forced_Disable mode
during which the laser is turned OFF. The laser have to be
turned ON during power up sequence by setting Forced_
Disabled bit (Bit-0) of LASER_CTRL0 register to 0.
5.
6.
Disabling the Laser
LASER_NEN is connected to the gate of a P-channel MOS-
FET transistor, which, when ON connect VDD3 to the laser.
In normal operation, the LASER_NEN is low. In the case of
a fault condition, LASER_NEN goes high to turn the tran-
sistor off and disconnects VDD3 from the laser.
PixArt
recommends the microcontroller host resets the sensor
when FAULT bit (Bit-6) of Motion register is set.
7.
8.
9.
Laser Output Power (LOP) Testing
The pre-calibrated LOP can be measured for testing pur-
pose as per steps below
1. Power up, reset the sensor and download SROM.
2. Enable the laser by setting Forced_Disabled bit of
LASER_CTL0 register to 0.
3. Enable the Calibration mode by writing 010b to bits
[3,2,1] of LASER_CTL0 register to set the laser to
continuous ON mode.
4. Measure the LOP at the navigation surface plane.
10. If this power is obtained, the laser power adjustment
is completed.
11. If it was not possible to achieve the power target, set
the laser current to the minimum value by writing
0x00 to LP_CFG0 register and the complementary
value 0xFF to LP_CFG1 register.
12. Set the Range and Range_C bits in LASER_CTRL0 and
LASER_CTRL1 to 1 and 0 respectively, to choose to
the higher laser current range.
13. Program LP_CFG0 and LP_CFG1 registers with
increasing values to achieve an output power as close
to 506μW as possible without exceeding it.
All rights strictly reserved any portion in this paper shall not be reproduced, copied or transformed to any other forms without permission.
9
PixArt Imaging Inc.
E-mail:
fae_service@pixart.com.tw
PIXART [ PIXART IMAGING INC. ]
