STV-376-E01 STMICROELECTRONICS [STMicroelectronics], STV-376-E01 Datasheet - Page 18

• Manufacturer Part Number: STV-376-E01
• Description: Ultra-low power laser motion sensor for laser mouse applications
• Manufacturer: STMICROELECTRONICS [STMicroelectronics]

Laser
6.2
6.3
18/30
Laser or led system managed by host (external micro)
The host must first select LED or LASER (bit [1] of register 0x05).
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Laser fault detection and safety feature
The sensor includes a set of diagnostic features that can be carried out at power-up (before
setting host_config_done). The tests listed below can be selected.
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If the result of these tests is a pass then the MCU can set the laser system as follows:
1.
2.
3.
LED
The host must select if the LED is to be driven by the internal DAC or an external
current supply using bit [5] of register 0x05 (led_dac_driven). Bit [3] of register 0x05
(host_config_done) then needs to be set.
–
–
LASER
The host must first decide whether to perform LASER fault detection (described in
Section
If the system passes the laser fault detection (or laser fault detect was not performed),
the host can then adjust the LASER DAC current by writing a value to bits [0-6] in
register 0x0A AND writing its complementary value to bits [0-6] of register 0x0D, if the
values are not compatible the VT5376 applies the minimum DAC current.
Check LASER_OUT is not shorted to VDD (LASER_OUT < 1.2V).
–
Check LASER_OUT and RBIN are not shorted to GND (LASER_OUT and
RBIN > 0.4V).
–
Set bit [3] of register 0x05 (host_config_done).
Write 0x25 (laser_drive and laser_nen enable) in register 0x0B (Top_laser_setting).
Write the required DAC value (bits 0-6) in register 0x0A (Top_laser_DAC_setting)
ensuring that force_laser_out_on = 0. Write the 1’s complement value of the above
setting in register 0x0D (Top_laser_Dac_setting_C).
Case internal DAC drive: VT5376 sets the maximum current from the DAC and
the system starts running.
Case external drive: VT5376 powers down its laser_drive and the led_on signal
is present on the LASER_NEN pin.
Enable DAC and disable OUT_HIGH switch by writing 0xF7 to register 0x0B (Top_
laser_setting), then make force_laser_out_on = 1, by writing 0x01 to bit 7 of
register 0x0A (Top_laser_DAC_setting), and 0 to it’s complementary bit (bit 7) in
register 0x0D (Top_laser_Dac_setting_C). Finally read bit 6 of register 0xC to
ensure that laser_low = 1.
External LASER_NEN switch must be fitted in order to make LASER_OUT go
below 0.4V.
Disable DAC and enable OUT_HIGH switch (force_laser_out_high = 1) by writing
0xFE to register 0x0B (Top_laser_setting). Then read register 0x0C
(Top_laser_diagnostics) to ensure that bit 7 (laser_high) is set to 1 and bit 5
(Rbin_low) is set to 0.
6.3) then set bit [3] of register 0x05 (host_config_done).
VT5376