Frequently asked questions about laser driver

Time : Sep 04 2018Source :analogtechnologies Author : Analog Click :

1. Does heat dissipation need to be provided during the use of the laser driver?

A. The higher the operating temperature of the laser driver, the greater the loss of its operating efficiency, the greater the noise, and therefore the worse the current stability. Its operating case temperature is −40°C ~ 85°C, We recommend that its working temperature be around 50°C.

B. If the surrounding environment is well ventilated, no heat sinks are needed, if the ventilation is not good, heat sinks are required.

2. How to use a laser driver will improve its efficiency?

A. There are linear mode laser driver and switch mode laser driver. For switch mode laser driver, it features high efficiency, but high noise and low modulation speed.

B. Both switch mode laser driver and linear mode laser driver, the closer the laser driver output voltage is to the input voltage, the higher efficient it is. But they all have a maximum voltage drop. The maximum voltage drop of ATLSxA103 cannot exceed 0.8V, the maximum voltage drop of ATLSxA104 cannot exceed 1.5V.

3. What is the difference between GND and PGND in laser driver?

GND is the signal ground and PGND is the power ground.

4. Why is the current of laser driver uncontrolled?

Because the PCN pin is pulled high to an internal 4.5V rail by a 1MΩ resistor and there is a serial 20kΩ resistor between PCN and the electronic switch. When PCN pin is low, the laser driver will output the current set by LISL. When PCN pin is high, the laser driver will output the current set by LISH.

5. Why design LISH and LISL two ports?

A. In some applications, the laser needs to jump between two currents.

B. If you enter a digital square wave with noise, the voltage is not stable. Get a logic high by LISH port and get a logic low by LISL port. A stable low-noise square wave is converted by PCN pin

6. What are the characteristics of switch mode laser drivers?

Switch mode laser driver noise has two frequencies, corner noise: 15µAP-P @0.1Hz~10Hz and ripple noise: 0.1Vp-p ripple voltage at 500kHz.

7. Is there any way to monitor the output current of the laser driver?

Yes. Laser driver is used with an evaluation board usually. The output current can be measured by a current meter, which can be inserted between the 2 multi-meter lead sockets: AMMTR+ and AMMTR−, which is located on the lower edge of the evaluation board. When an Ammeter is inserted into the circuit, turn switch S5 onto the upper position, the open circuit the meter leads, so that the current will go through the meter, thus the current will be measured.

More information about laser drivers, please see here: