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Analog Technologies

ATLS500MA106

Low Noise Constant Current Laser Controller

Figure 8.2 Transferring Heat with Heat Sink

First Time Power Up

Laser is a high value and vulnerable device. Faults in

connections and damages done to the controller during

soldering process may damage the laser permanently.

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

regular diodes of >200mA to form a “dummy laser” and

insert it in the place of the real laser diode, when powering

up the controller for the first time. Use an oscilloscope to

monitor the LDA voltage at times of power-up and power-

down, make sure that there is not over-shoot in voltage. 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 free of faults, disconnect the

dummy laser and connect the real laser in place.

The controller output voltage range for the laser is between

0.5 to 4V when powered by a 5V power supply.

Bandwidth Measurement

The controller bandwidth is 100kHz. There are two

methods to measure the bandwidth: large signal modulation

and small signal modulation. The measuring methods are as

below.

Small Signal Modulation Definition

Figure 9.1 Small Signal Modulation

As shown in Figure 9.1, add a sine signal of 1V DC + 0.2

then measure the AC voltage on LIS and LIO. The AC

voltage ratio of LIO (AC)/LIS (AC) is 0.707 at the

frequency of around 200kHz, see Figure 9.2

Figure 9.2. The Ratio of LIO/LIS

Large Signal Modulation Definition

Figure 10. Large Signal Modulation