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Analog Technologies

ATLS3A201D

Constant Current Laser Driver

thermally conductive. One of such products is the

T-flex 200 filler sheet made by Lairdtech, the available

thickness is between 1mm to 4mm. More detail technical data

To minimize the power consumed by the driver, VPS can be

set to such as a value that the maximum LDA voltage is

enough to cover the maximum forward voltage of the laser

diode. The maximum forward voltage of the laser diodes can

be found from the laser diodes’ datasheets.

Using a 3.3V power supply is enough for certain wavelength

laser diodes, while shorter wavelength laser diodes may

require 5V power supply. However, using a 3.3V power

supply results in a much lower power consumption by the

driver than using a 5V power supply.

First Time Power Up

Laser diode is a high value and vulnerable device. Faults in

connections and damages done to the driver during soldering

process may damage the laser diode permanently.

To protect the laser diode, it is highly recommend to use 3 to 4

regular diodes of >6A to form a “dummy laser” and insert it in

the place of the real laser diode, when powering up the driver

for the first time. Use an oscilloscope to monitor the LDA

voltage at times of powering up and enabling the shutdown

pin, and powering down the laser driver and turning off the

shutdown pin, and make sure that there is not over-shoot in

output voltage at the LDA pin. At the same time, use an

ammeter in serious with the dummy laser, to make sure that

the output current is correct.

After thorough checking and making sure free of faults in the

system, disconnect the dummy laser diode and connect the

real laser diode in place.

Driving High Voltage Laser Diodes

Some laser diodes have high forward voltage, such as 7V,

while the laser driver ATLS3A201D has a maximum output

voltage of 4V. This section tells a way to drive such laser

diodes by using this laser driver.

The schematic is show as in Figure 10. Where Power Supply

1 is the power supply for the laser driver, Power Supply 2 is

for increasing the laser driver's maximum output voltage.

Please notice that the power on sequence has to be in this way:

turn on Power Supply 1, turn on Power Supply 2, then turn on

the laser driver by driving SDN (Shutdown) pin to logic high.

The sequence for turning off the laser circuit is: turn off the

SDN pin by pulling it down to the logic low, turn off Power

Supply 1, then, turn off power supply 2.

To make sure the circuit works ok: turn on the laser, measure

LDA voltage, it should be between 1V to 3V, at room

temperature, the ideal LDA voltage is around 2V.