iC-WJ, iC-WJZ
LASER DIODE DRIVER
Rev C1, Page 9/12
time. The watchdog begins to discharge the capacitor
CI current limited. The remaining charge time during
the pulse pauses before further watchdog intervention
is not sufficient to maintain the initial potential at CI.
The potential is thus gradually reduced until it reaches
the saturation voltage
Vs(CI)
wd
(Electrical Character-
istics No. 405).
The watchdog therefore protects the laser diode from
destruction when the input signal change in such a
manner that the capacitor CI is not longer adequate
for averaging.
Furthermore, the introduction of the watchdog permits
long pulse pauses and activation of the laser diode with
pulse packets.
C1
10 uF
R1
12
Ω
C3
5 nF
1
GND
KLD
AMD
8
LD
MD
2
CWD
CI
100 nF
3
CI
WDOG
7
IN
REF
6
RSET
10 kΩ
4
ISET
iC−WJ/WJZ
VCC
5
C2
100 nF
+5 V
Figure 10: CW operation via cable
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. 12
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.
ICHAUS [ IC-HAUS GMBH ]
