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3

Analog Technologies

ATLS3A201D

Constant Current Laser Driver

OPERATION PRINCIPLE

The block diagram of the driver is shown in Figure 3. The

shut down control circuit accepts signals from 3 sources:

external shut down, over current and over temperature

signals. When any of these signals is activated, the driver is

shut down. Only when none all these 3 signals is activated, a

soft start circuit starts enabling the driver stage.

The soft start circuit increases the output current slowly at

the start up time and shuts down the current quickly.

Thermal shutdown circuit turns the driver off if the junction

temperature exceeds 150°C. The driver is released from

shutdown automatically when the junction temperature

decreases to 10°C below the thermal shutdown trip point,

and starts up under control of the soft start circuit. The over

current protection circuit turns the driver off if the output

The high stability low noise 2.5V voltage reference is

provided for setting the output current by setting the LIS’

voltage, and can also be used for the ADCs and/or DACs.

The laser diode status indication circuit monitors laser diode

status. When LDGD pin is high, >2V, the control loop is

working properly; when this pin goes low, <0.3V, the laser

diode is bad, or there is a short or open circuit at the laser

diode.

The laser current control indication circuit shows the driving

status for the output current. When this voltage is between

0.2V to 1.8V, the output voltage on the laser diode is

between 4.8V to 0V.

The current measurement circuit monitors the output current

and shuts down the driver upon detecting the output current

exceeds the pre-set value. It also provides a signal, LIO,

indicating the actual laser diode current. The relationship is:

driver

EA

LDA

LIS

PGND

LIO

LIGD

9

5

6

8

10

Over current

protection

Current

measurement

Laser

diode

& thermal

shutdown

Laser

diode

voltage

Constant

current

2.5V

reference

Soft start

LDGD

2

SDN

1

2.5VR

4

indication

status

Laser current

control indication

Figure 3. Block Diagram

APPLICATION INFORMATION

To power GND

+5V

LIO

6

VPS

12

PGND 10

LIGD 8

LDA 9

GND

3

2.5VR

4

LIS

5

PGND 11

GND 7

LDGD

2

SDN

1

Laser Driver

A

K

Laser diode

D2

(Clock-wise)

S1 Shutdown

A

K

D1

LED

To DC voltmeter

To DC voltmeter

To signal GND

3

1 W1 10K

Figure 4.1. A Typical Stand-alone Application Schematic for ATLS3A201D

LDC

LDC