PixArt Imaging Inc.
Track-on-Glass Laser Sensor
Single Fault Detection
The sensor is able to detect a short circuit or fault condi-
tion at its internal laser’s cathode node, which could lead
to excessive laser output power. A leakage path to ground
on this node will trigger the fault detection circuit, which
will turn off the laser drive current source and set the in-
ternal signal of LASER_NEN output high. The system will
prevent excessive laser power by shutting off the laser.
In addition to the ground path fault detection described
above, the fault detection circuit is periodically checking
for proper operation by internally generating a path to
ground with the laser turned off via LASER_NEN. If the la-
ser cathode is shorted to VDD3, this test will fail and will
be reported as a fault.
VDD3
S
Microcontroller
LASER DRIVER
LASER_NEN
G
P_MOSFET
VDD3
D
fault control
block
Serial Port
-VCSEL
+VCSEL
voltage sense
VCSEL
22nF
current set
GND
Figure 7. Single Fault Detection and Eye-safety Feature Block Diagram
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PixArt Imaging Inc.
E-mail: fae_service@pixart.com.tw
10
PIXART [ PIXART IMAGING INC. ]
