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4

Analog Technologies

Evaluation Board for ATLS201D

ATLS201DEV1.0

B. The Ammeter has voltage drop, which decreases the

maximum output voltage.

C. If the Ammeter is not connected well or there is an

intermittent disconnection at any portion of the

circuit, the real laser may be damaged permanently.

If the user really needs to do it in this way, this is the

procedure:

A. Use the terminal block on the right side, the 3rd and

the 4th conductors, insert the Ammeter between

AMMTR+ pin and AMMTR

− pin.

B. Turn the switch S7 to its lower off position, thus the

output current can go through the ammeter and be

measured by reading Ammeter’s value.; when the

switch S7 is placed in the upper on position, the

ampere meter is shorted, thus, it does not measure the

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 driver 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 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

S2 to the on position (upper), to connect the “dummy

laser” to the driver. Turning switches S3, S4, S5 and S6,

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 4A. Warning: when

output 4A current, the diodes may get very hot, don’t

touch them with your fingers. 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 driver will

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

internal temperature protection circuit will shut off the

driver automatically. When this happens, wait for a few

seconds, let the driver cool down, the driver will restart by

itself again after the temperature is lowered to certain

level. This is the way to calculate the power consumption

of the driver:

also the voltage across the laser diode.

Switch Name

Corresponding Diode

S3

Diode D1

S4

Diode D2

S5

Diode D3

S6

Diode D4

7. Disconnect the dummy laser from the driver. This can be

simply done by turning switch S2 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 driver pin

via. If the driver works well, the output current should

remain the same as the output voltage changes.

9. Set the output current. Adjusting the potentiometer W1

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

driver, the actual controllable minimum current is about

10nA, the lowest one available on the market to our

output current is:

X is maximum output current, 2A, 4A, 3A or 6A;

10. 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

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

because the output current exceeding the current limit.

11. Loop good indication. When the driver 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 driver is being shut off or the output

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

12. 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, for example LIO, and the DACs can also be utilized

for setting the LIS and/or LDGD pin voltages. The