VT5376 View Datasheet(PDF) - STMicroelectronics
Part Name
Description
MFG CO.
'VT5376' PDF : 24 Pages View PDF
VT5376
Laser
6.2
Laser or led system managed by host (external micro)
The host must first select LED or LASER (bit [1] of register 0x05).
● 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.
– 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.
● LASER
The host must first decide whether to perform LASER fault detection (described in
Section 6.3) then set bit [3] of register 0x05 (host_config_done).
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.
6.3
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.
● Check LASER_OUT is not shorted to VDD (LASER_OUT < 1.2V).
– 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.
● Check LASER_OUT and RBIN are not shorted to GND (LASER_OUT and
RBIN > 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.
If the result of these tests is a pass then the MCU can set the laser system as follows:
1. Set bit [3] of register 0x05 (host_config_done).
2. Write 0x25 (laser_drive and laser_nen enable) in register 0x0B (Top_laser_setting).
3. 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).
Doc ID 13939 Rev 4
19/31
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