9

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.

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.

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.

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.

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.

The ambient temperature should be 25°C ± 5°C.

2.

Set VDD3 to the typical recommended operating

voltage.

3.

Power up,reset the sensor and download SROM

4.

Enable the Calibration mode by writing 010b to Bit-

[3, 2, 1] of LASER_CTRL0 register to set the laser to

continuous ON mode.

5.

Set the Range bit (Bit-7) of LASER_CTRL0 register to 0.

6.

Set

the

Range_C

bit

(Bit-7)

of

LASER_CTRL1

complement to setting of Range bit in LASER_CTRL0

register.

7.

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.

8.

Set the laser current to the minimum value by writing

0x00 to LP_CFG0 register and the complementary

value 0xFF to LP_CFG1 register.

9.

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.

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.

PixArt Imaging Inc.

Track-on-Glass Laser Sensor

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PixArt Imaging Inc.