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7

Analog Technologies

ATLS100MA103

Low Noise Constant Current Laser Controller

The laser’s threshold current is shown in Figure 11. It can be

seen that when the laser’s current fall below a certain value,

there is no output optical power. For example, the operating

current and threshold current of a red laser diode of 650nm

are 30mA and 20mA respectively and the optical output

power is 4mW. It will have no optical output power if the

output current of this laser diode is lower than 20mA which is

its threshold current. Figure 12 and Figure 13 will describe

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:

× 25 (V).

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

output current is 100mA.

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.

(t)

2.5V

(t)