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7

Analog Technologies

Low Noise Constant Current Laser Controller

ATLS250MA103

× 10 (V).

For example, when the output signal equals to 2.5V, the

output current is 250mA.

The output impedance of this pin is 10

Ω and it can be used to

drive an ADC directly.

It can also be measured by a multimeter during debugging

process.

Monitoring the Controller Internal Temperature

The controller internal temperature can be monitored by

measuring the TMPO pin voltage. The relationship between

the LMPO voltage and the temperature is:

)

(

479

.

3

8015

.

1

4182

.

2

10

04

.

1525

3

C

TMPO

T

°

−

+

+

−

=

(1)

Where TMPO is the voltage on the TMPO pin.

This formula can be approximated by a linear equation:

)

(

31

.

90

7

.

192

C

TMPO

T

°

×

−

=

(2)

Within the most commonly used temperature range of

between 0

°C to 100°C, the maximum error occurs at about

1.5V, at which the temperature error between the calculated

data by using the formula (1) and the approximated data

obtained by using the linear equation (2) is about 0.4

°C, with

the linear data being a little lower. The curves of the 2 sets of

the data are plotted in Figure 16.

Please notice that the TMPO pin has a weak driving

capability: the maximum sourcing current is 1

μA and the

maximum sinking current is 40

μA.

The TMPO pin can also be used as an input control pin: when

forcing the TMPO voltage to below 0.4V, the laser controller

will be shutdown.

Controller Power Consumption

The power consumption of the controller can be calculated by:

Under this situation, if prefer not to use the heat sink, this is

an option: lowering the controller power consumption by

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 >100mA 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 series 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

Driving High Voltage Laser Diodes

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

while the laser driver ATLS250MA103D 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 shown in Figure 15, 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.

Toc 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.

(t)

2.5V

(t)