iC-WJB

2.7 V LASER DIODE DRIVER

Rev E1, Page 9/12

Furthermore, the introduction of the watchdog permits

long pulse pauses and activation of the laser diode with

pulse packets.

AMD

2.7..6V

7

3

CI

2

CWD

1

GND

6

IN

4

ISET

8

KLD

5

VCC

MD

LD

S1

100nF

CI

15k

Ω

RSET

C3

4.7nF

iC−WJB

REF

WDOG

R1

D1

ZD6V8

C2

100nF

R2

2

Ω

47uF

C1

VCC

KLD

AMD

LD supply cord

0..2

Ω

Figure 10: CW operation via cable plus protective circuitry

CW Operation

In case of CW operation, the input IN can be con-

nected to the power supply VCC. The pin CWD may

be left open, because the capacitor for the watchdog

is not necessary. The capacitor CI for the averaging

control can be reduced to 100 nF.

Operation of laser diode via cable

It is recommended to connect a capacitor of 1 to 10 nF

across the laser diode in order to protect the laser

diode against destruction due to ESD or transients.

This capacitor should be placed close to the laser

diode and not at the beginning of the LD supply line.

An approx. 2 Ω series resistor at pin KLD reduces

the IC power consumption and damps possible reso-

nances of the load circuit caused by the inductive LD

supply line. This resistor is useful for many applica-

tions, also for those which do not operate via cable.

On a PCB the forward path VCC to the laser diode

should be arranged in parallel with the return path to

KLD even when the line is only a few centimeters in

length.

Additional protective components for clipping of strong

positive and negative spikes can be useful, in particu-

lar when contact bouncing occurs in an inductive accu-

mulator power supply line. Elements which come into

question here are D1 and R1 as in Figure 10.