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7

Analog Technologies

ATLS100MA104

Low Noise Constant Current Laser Controller

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:

×2.5 (V)/100mA.

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.

Figure 9. LIO is Controlled by LIS and Clamped by LIMS

When the output current set by LIS is less than the current

with LIS linearly; when output current set by LIS exceeds

value set by the LIMS, see Figure 9.

Monitoring the Controller Internal Temperature

The controller internal temperature can be monitored by

measuring the TMPO pin voltage. The relationship

between the TMPO voltage and the temperature is:

)

(

479

.

3

8015

.

1

4182

.

2

10

04

.

1525

3

C

V

T

−

+

+

−

=

(1)

This formula can be approximated by a linear equation:

)

(

31

.

90

7

.

192

C

V

T

TMPO

°

×

−

=

(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 20.

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 shut down.

Controller Power Consumption

When the maximum power consumed by the controller is

maintained to <1W, it does not require a heat sink to

operate. The power dissipated by the controller can be

calculated by this formula:

going through the load.

Figure 10 shows the current distributions of the controller.

Figure 10. The Current Distributions in the Controller

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

is an option: lowering the controller power consumption by

voltage.