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4

Analog Technologies

Evaluation Board for ATLS1A103D

ATLS1A103DEV1.0

output current, see the schematic shown in Figure 7.

C. Set the Ammeter to a fixed gain or the high value setting,

such as 10A. Otherwise, the automatic ranging setting

circuit of the Ammeter may cause some noise to the

laser when the current range setting is switched inside

the Ammeter.

6. Test the controller with the “dummy laser”. The 5 diodes

on the board, D1 to D5, can form a “dummy laser” to act as

the laser diode in the place of a real laser so that in case

there is a problem in the circuit, the expensive laser would

not be damaged, see schematic in Figure 7. Turn the switch

S1A to the on position (upper), to connect the “dummy

laser” to the controller. Turning switches S1B, S1C, S1D

and S1E, up and down will increase (turning down the

switches) and decrease (turning up the switches) the

forward voltage of the “dummy laser” which can be

measured by a volt meter between the LDA and the ground.

Each diode can increase or decrease the output forward

voltage by about 0.7V when the output current is 1A.

Warning: when output 1A current, the diodes may get

very hot, don’t put your fingers on them. The switch

bank and their corresponding diodes are shown in the table

below. The diode D5 is always activated so that the total

forward voltage range is from 0.7V to 0.7V + 0.7

×4 = 3.5V.

Please be aware of this fact: when the output voltage is low

by shorting circuit all the diodes, the controller will need to

consume a lot of power and may get too hot that the

internal temperature protection circuit shut off the

controller automatically. When this happens, wait for a few

seconds, let the controller cool down, the controller will

restart by itself again after the temperature is lowered to

certain level. This is the way to calculate the power

consumption of the controller:

output voltage which is also the voltage on the LDA pin.

The unit is power. When the controller is placed in a free

air, the thermal resistance is about 60

°C/W.

Table 2. The switch controls corresponding diode

Switch Name

Corresponding Diode

S1B

Diode D1

S1C

Diode D2

S1D

Diode D3

S1E

Diode D4

7. Disconnect the dummy laser from the controller. This can

be simply done by turning switch S1A to its lower off

position.

8. Monitor the output voltage. This can be done by using a

volt meter to measure the voltage between LDA and ground.

This node is available at the edge pad (upper right corner),

the terminal block conductor, and the controller pin via. If

the controller works well, the output current should

remain the same as the output voltage changes.

9. Set the output current. Adjusting the potentiometer W2 will

set the output current from 0 to 1A by changing the voltage

on the LIS pin. Due to the low noise nature of the controller,

the actual controllable minimum current is about 10nA, the

lowest one available on the market to our knowledge. The

relationship between the LIS voltage and the output current

is:

current of the laser driver in the evaluation board, and LIS

stands for the voltage at the LIS pin.

The output current follows the LIS pin voltage only under

these conditions:

A.The output forward voltage of the load is lower than 4V

at the current desired to set.

B.The current limit is higher than the set-point current

desired to set. The output of the laser.

Please notice that the potentiometer W2 set the voltage on

the node LIS1, which results in a low-pass filtered low

noise voltage. This voltage goes through switch S1G and is

connected to the LIS pin of the controller when the switch

S1G is on the upper on position. In case the LIS pin needs

to be controlled by another external signal source for

modulating the output current, turn this switch S1G on the

lower that is off position, to disconnect the LIS pin from the

LIS1 node.

Since the LIS1 node has a high internal impedance, around

1MΩ, do not use a voltmeter to probe this pin for

measuring the voltage, otherwise error will occur because

the internal resistance of the voltage meter will lower the

output voltage on the LIS1 node.

To measure the LIS1 voltage accurately, use a voltmeter to

probe the LISET node, which is made accessible on the

solder pad or the terminal block conductor of TB1, all on

the left side of the board.

10.Set the output current limit. Adjusting the potentiometer

W1 will set the output current limit from 0 to 1.1A by

setting the voltage on the LILM pin. The relationship

between the LILM voltage and the output current is:

×1.1×LILM/2.5V (A),

maximum current of the laser driver in the evaluation board,

and LILM stands for the voltage at the LILM pin.

When the output current set by the LIS pin goes higher than

the current limit set by the LILM pin, the controller will

turn off the controller; after being turned off, the controller