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3

Analog Technologies

ATLS3A202D

Constant Current Laser Driver

driver

EA

LDA

LIS

PGND

LIO

9

5

6

10

Over current

protection

Current

measurement

Laser

diode

& thermal

shutdown

Laser

diode

voltage

Constant

current

2.5V

reference

Soft start

LDGD

8

SDN

1

4

2.5VR

indication

status

Figure 3. Block Diagram

APPLICATION INFORMATION

To power GND

To power supply

A

K

Laser diode

D1

(Clock-wise)

S1 Shutdown

A

K

D2

LED

To external clock

To DC voltmeter

3

1 W1 100K

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 4. A Typical Stand-alone Application Schematic

Figure 4 shows a typical stand-alone application circuit.

The switch S1 is an external switch for shutting down or

enabling the controller. When shorting SDN to ground, i.e.

to close the switch S1, the controller is shut down; when

leave the switch open, the internal pull up circuit pulls the

SDN pin high and the controller is enabled. The internal

logic threshold on the SDN pin is: >1.4V for enabling, and

<0.95V for shutting down, normal threshold voltage is

1.2V. The switch S1 can also be replaced by an electronic

switch, such as an I/O pin of a micro-controller, an either

open drain or push-pull output digital port, see Figure 5. If

not using a switch to control the laser, leave the SDN pin

unconnected.

The SYNC pin is for using an external signal to

synchronize the internal switching frequency, to eliminate

the beating interference between this laser controller and

other switch mode power supply on the same PCB. If the

SYNC is not connected, the default internal switching

frequency is 500kHz. When using this pin, it must be

connected by an external clock signal of about 550kHz to

570kHz, about 10% to 15% higher than the default

switching frequency of 500kHz. After using this function,

the driver will be switching at the same frequency with the

external clock signal, eliminating beating interferences. If

other switching frequency is needed, please contact us, it

can be specified from 300kHz to 700kHz.

In Figure 4, the potentiometer W1 is used to set the output

current. Setting LIS from 0V to 2.5V will set the laser

current from 0 to 3A linearly.

The laser diode D1 is connected between LDA and LDC

pins. It is worth mentioning that the power supply return

terminal should be connected to the pin 11, PGND, and the

cathode of the laser diode should be connected to the pin

10, LDC. These 2 nodes should not be connected together

externally, although they are connected together internally

already by the driver circuit.

In Figure 4, the LED D2 is used to indicate laser diode

status. When LDGD pin is high, >2V, the laser diode

control loop is working properly. When LDGD pin is low,

<0.3V, the laser diode is bad, or there is a short or open

circuit at the laser diode. The LDGD pin can also be

connected to a digital input pin of a micro-controller, when

LDC

LDC

LDC