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4

Analog Technologies

ATLS3A202D

Constant Current Laser Driver

software/firmware is utilized in the system, see Figure 5. A

typical micro-processor-based application circuit is shown

in Figure 5.

To ADC & DAC

To ADC

To micro-controller

To micro-controller

To signal GND

To power GND

To power supply

To DAC

To signal GND

To external clock

A

K

Laser diode

D1

LIO

6

VPS

12

PGND

10

LDGD

8

LDA

9

GND

3

2.5VR

4

LIS

5

PGND 11

GND 7

SYNC

2

SDN

1

Laser Driver

Figure 5. A Typical Micro-processor-based Application Schematic

Turning the Driver On and Off

The driver can be turned on and off by setting the SDN pin

high and lower respectively. It is recommended to turn the

driver on by this sequence:

To turn on: turn on the power by providing the power supply

voltage to the driver, turn on the driver by releasing the SDN

pin.

To turn off: turn off the driver by lowering the voltage of

SDN pin, turn off the power by stopping the voltage supply

on the VPS pin.

When not controlling by the SDN pin: leave it unconnected

and turn on and off the driver by the power supply.

Adjusting the Output Current

The output current is set by adjusting W1, which sets input

voltages on LIS, pin 5, see Figure 4. The output current will

be:

LIS can be configured by using a DAC, to replace the W1 in

Figure 4. Please make sure that the DAC has a low output

noise, or, if no modulation is needed, an RC low pass filtered

can be inserted between the DAC and the LIS pin.

The LIO pin indicates the actual output current of the laser

controller. It can still be used to monitor the output current.

When this pin’s voltage changes from 0V to 2.5V, it

indicates the laser current is from 0 to 3A linearly.

Monitoring the Output Current

The output current of the driver can be monitored by

measuring the voltage on the LIO pin. This feature is very

useful for micro-controller based system where an 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:

For example, when the output current is 3A, the LIO pin

voltage is 2.5V.

The LIO pin can be used to drive an ADC directly, or

measured by a multimeter. Please be aware of this: using a

digital multimeter to measure the LIO pin’s voltage may

inject noise which is generated by the digital circuit of the

meter, this noise can be amplified by the laser controller and

shows up at the output pin, LDA. Therefore, it is not

recommended to use a digital meter to measure the LIO pin’s

voltage when the laser is working.

Normal

Operation

Region

3.3

5

0.2

4.0

2.4

(V)

Driver Power Consumption

The power consumption of the driver can be calculated by:

LDC