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7

Analog Technologies

Low Noise Constant Current Laser Controller

ATLS200MA103

Monitoring the Output Current

The output current of the controller can be monitored by

measuring the voltage on the LIO pin. This feature is very

useful for micro-controller based system where the ADC is

available and monitoring the current in real time is required.

This pin provides a very low noise voltage signal which is

proportional to the output current:

× 12.5 (V).

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

output current is 200mA.

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 17.

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:

The best way for arranging the heat sinking for the driver is as

follows: transferring the heat by sandwiching a piece of

thermal conductive pad between the top metal surface of the

laser driver and the internal metal surface of the final product

as shown in Figure 15.1 and 15.2 below. The recommended

thickness of the thermal conductive pad in Figure 15.1 is

1~4mm, and in Figure 15.2 is 0.5mm. ATI also provides a

series of thermal conductive pads, click here for more

information.

If prefer not to use the heat sink, this is an option: lowering

the controller power consumption by reducing the power

(t)

2.5V

(t)