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5

Analog Technologies

Evaluation Board for ATLS1A103D

ATLS1A103DEV1.0

restarts by itself and ramp up the output current by the soft

start circuitry, if the output current still goes beyond the

current limit, the controller shuts off again and repeat the

resetting process. The laser is thus protected from being

damaged by over current. The output current is a saw-tooth

shape signal under protection mode.

11.Modulate the output current by an external signal source.

This can be done by connecting the external signal source

to the LIS node, which is accessible by the LIS solder pad

or the LIS conductor on the terminal block TB1, both on

the left side of the board. Make sure:

A.The peak of the signal will not set the output current to

too high a value that may damage the laser diode, if a real

laser is connected to the output.

B.The current limit is set to a proper value, thus, the

controller will not be shut-off by the current limit circuit

because the output current exceeding the current limit.

C.The switch S1G is turned to the lower off position, thus,

the LIS pin will solely controlled by the external source

signal, not by the LIS1 node.

D. The control bandwidth of the LIS pin is around 2MHz,

that is: when inputting a pure square wave signal to the LIS

pin, the rise and fall time of the output current will be about

0.35/2MHz = 175nS (nano-second). Please be aware of this:

the output current should be seen on an oscilloscope by

probing the LIO pin. Probing LDA pin will see a distorted

version of the output current because the dummy load or a

real laser diode is a non-linear device and also has

capacitance between the 2 terminals, thus the voltage

waveform is not always proportional to the current

waveform.

12.Loop good indication. When the controller works perfectly,

i.e., the output current equals the set-point current set by

LIS pin, the LED on the lower right corner of the board will

be lit up. Otherwise, it will be dark when the power supply

is on and the controller is being shut off (turning the

shutdown switch S1H to upper position) or the output

voltage is beyond 4V at the current set by the LIS pin.

13.Monitor the internal temperature of the controller. 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

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 8.

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.

14.Connecting external ADCs (Analog to Digital Converters)

and DACs (Digital to Analog Converters). The ADCs can

be utilized for monitoring the analog voltages on certain

pins, such as LIO, TEMPO, LISSET, etc., and the DACs

can also be utilized for setting the LIS and/or LISLM pin

voltages. The voltage reference from the controller can be

used as the voltage reference for the ADCs and DACs.

15.Connecting a real laser diode to the evaluation board. After

making sure that the controller works properly by going

through the above steps, a real laser diode can be connected

to the evaluation board. This is the procedure:

A. Set the output current and the current limit to the values

desired by driving the dummy laser on the board as

described above. The current limit is usually set to the

1.1 times of the output current.

B. Solder the laser diode terminal wires to the LDA and

LDC solder pads, or use the LDA and LDC conductors

on the terminal block TB3 and lock the wires by using

the screws. Make sure that the connections are tight and

secure, no intermittent disconnection will occur.

C. Set the output forward voltage to 1.4V by switching

S1A, S1B, S1C and S1D to the upper on position. Turn

on the power supply, and see everything works perfectly

as described above.

D. Turn off the power, turn the switch S1A to the lower off

position and turn on the power again. After this moment,

be more careful in doing anything on the board, because

any mistake in operating the board or causing

intermittent disconnections for any connections on the

board may result in damaging the laser diode

permanently.

E. If everything still works fine after step D above, the user

can proceed to testing the laser itself. The output current

and current limit can be adjusted while the laser is

turned on, but make sure that the output current will

never exceed the laser’s current limit.

F. In case there are any suspicious or real problems,

disconnect the real laser and use the dummy laser for

debugging.