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Analog Technologies

ATLS3A212

High Voltage Constant Current 3A Laser Driver

APPLICATION INFORMATION

Figure 7. A Typical Stand-alone Application Schematic

Figure 7 shows a typical stand-alone application circuit.

Digital signal V1 and V2 control the laser driver into

Shutdown, Standby or Operation mode. The starting up time

delay is about 20mS and the shut down time is about 20µs.

It is worth mentioning that to achieve high speed and low

distortion digital modulation, one can use the LISL pin to set

a current that is a little lower than the threshold current of

the laser diode to turn off the laser beam, such as half of its

value, use the LISH pin to set the laser current when the

laser diode is turned on. In this way, the laser beam is turned

on and off, while the driver control loop is always kept on,

so that the output stage is always under control, no distortion

is caused by turning on/off the output stage.

When no modulation is needed, one can leave PCN pin

unconnected, LISL connect pin to GND, and use LISH to

set the output current.

In Figure 7, the LED is used to indicate laser diode status.

When LPGD pin is high, >2V, the laser diode control loop is

working properly. When LPGD pin is low, <0.3V, the laser

diode control loop is not working properly, there might be a

short or open circuit at the laser diode, or the laser driver is put

into Standby or Shutdown mode. The LPGD pin can also be

connected to a digital input pin of a micro-controller, when

software/firmware is utilized in the system. See Figure 7. The

equivalent circuit of LPGD pin is a 3k

Ω resistor pulling up it to

4V rail and an open drain FET, 500

Ω, pulling it down to the

ground. The pull-up current can be increased by connecting an

external pull-up resistor between LPGD and VPS. Tie this

added additional pull up resistor to a 3.3V or 5V power supply

if they are available. Make sure that the pull up current is not

too high, otherwise, the internal open drain FET cannot pull-

down the LPGD pin low enough to turn off the LED.

The laser diodes are connected between LDA and LDC pins. It

is worth mentioning that the power supply return terminal

should be connected to the pin 12 PGND.