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3

Analog Technologies

ATLS2A202D

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

APPLICATIONS

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.

In Figure 4, the switch S1 is external shut down switch, it

can turn on and off the driver with the SDN pin high and

lower respectively, at the internal chip control input: >1.4V

= enable, <0.95V = shut down, normal threshold voltage =

1.2V. The switch S1 can also be an electronic switch, such

as an I/O pin of a micro-controller, with an either open

drain or push/pull output. See Figure 5. If not using a

switch (S1) to control the laser, leave the SDN pin

unconnected.

If the SYNC isn’t connected, the default internal switching

frequency is 500kHz.This pin can also be connected to an

external clock signal of which the frequency can be about

10% to 15% higher than the switching frequency. In this

way, the driver will be switching at the same frequency

with the external clock signal, eliminating beating

interferences. If other switching frequency is needed,

please tell us, it can be specified from 300kHz to 700kHz.

In Figure 4, the adjustable resistor W1 is used to setting the

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

laser current from 0A to 2A linearly.

The laser diode D1 is connected between LDA and LDC. 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

and they are connected together internally already by the

driver.

In Figure 4, the LED D2 is used to indicating 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

software/firmware is utilized in the system. See Figure 5.

Figure 5 shows a typical micro-processor-based application

circuit.

LDC

LDC