VT5376

Laser

17/30

6

Laser

6.1

Direct laser drive and calibration

The sensor includes a 7-bit DAC and an output current source.

The DAC value must be set via two I2C commands after power-up (default is MIN = 3.4mA,

with Rbin = 12K).

To allow VCSEL output power measurements to be done, the user can set the laser out

(normally strobed during operation) to continuously on via an I2C command. This feature is

optional and is designed to offer maximum flexibility.

Alternatively, the Idac maximum (up to a max = 13mA) and minimum values can be changed

by adjusting the Rbin value (for example, with Rbin = 24K, Idac max = 5mA and Idac min =

1.7mA).

Idac max is set by the formula:

Idac (max) = 120/Rbin (result in mA, Rbin in kohms)

No external driver is required, just a FET power switch controlled by LASER_NEN signal.

Figure 9.

Application schematics using Laser or LED (driven with internal DAC or external

current source)

LASER_NEN

LASER_OUT

RBIN

Laser system driven by internal DAC

laser_selected = 1

VTOP

VT5376

LASER_OUT

RBIN

LED system driven by internal DAC

laser_selected = 0

VTOP

VT5376

LASER_NEN

LASER_OUT

RBIN

LED system driven by external drive

laser_select = 0

VTOP

VT5376

led_dac_driven = 1

led_dac_driven = 0

laser

LED

LED

36X trk_led (active high)

LASER_NEN