iC-WJB

2.7 V LASER DIODE DRIVER

Rev E1, Page 6/12

APPLICATIONS INFORMATION

Laser Power Adjustment

The iC-WJB device can be adapted to CW laser diodes

of up to 40 mW. When the supply voltage is higher than

approx. 4.5 V, LD models in common cathode configu-

ration can be used.

The pin ISET is used for the adjustment to the sensi-

tivity of the monitor diode and to set the desired optical

laser power. The setpoint for the averaging control of

the monitor diode current is pre-set at this pin.

+5V

AMD

CI

CWD

GND

VCC

IN

ISET

KLD

MD

LD

24k

Ω

RSET

2

1

REF

VCC

REF

3

1

4

3

iC−WJB

C1

47uF

470nF

CI

0..2

Ω

R1

2nF

C3

4

6

2

3

1

7

8

5

REFERENCE

WATCHDOG

THERMAL

POWER DOWN

INPUT

DRIVER STAGE

SHUTDOWN

Figure 1: Circuit diagram for LD models with a common cathode

To calculate the current required at ISET, the average

optical laser power is to determine:

T

twhi

T

twlo

Figure 2: Duty cycle

Example for CW operation

diode maximum optical output of 3 mW, monitor diode

with 0.75 mA at 3 mW.

0.25 mA and RSET is calculated to:

RSET =

CR1 ∗ V (ISET )

=

3 ∗ 1.22 V

0.25 mA

= 14.64 k Ω

with Electrical Characteristics No. 301 for V(ISET) and

No. 107 for current ratio CR1.

Example for pulse operation

laser diode as above with maximum optical output of

3 mW, monitor diode with 0.75 mA at 3 mW.

The average optical power is set to 0.6 mW by the

pulse duty factor; the average monitor diode current

to: