iC-WJ, iC-WJZ
LASER DIODE DRIVER
Rev C1, Page 9/12
time. The watchdog begins to discharge the capacitor The watchdog therefore protects the laser diode from
CI current limited. The remaining charge time during destruction when the input signal change in such a
the pulse pauses before further watchdog intervention manner that the capacitor CI is not longer adequate
is not sufficient to maintain the initial potential at CI. for averaging.
The potential is thus gradually reduced until it reaches
the saturation voltage Vs(CI)wd (Electrical Character- Furthermore, the introduction of the watchdog permits
istics No. 405).
long pulse pauses and activation of the laser diode with
pulse packets.
C1
10 uF
C3
R1
5 nF
GND
KLD
12Ω
1
8
LD
MD
AMD
2
7
6
CWD
CI
100 nF
WDOG
3
CI
IN
REF
RSET
4
10 kΩ
5
ISET
VCC
+5 V
iC−WJ/WJZ
C2
100 nF
Figure 10: CW operation via cable
CW Operation
An approx. 12 Ω series resistor at pin KLD reduces
In case of CW operation, the input IN can be con- the IC power consumption and damps possible reso-
nected to the power supply VCC. The pin CWD may nances of the load circuit caused by the inductive LD
be left open, because the capacitor for the watchdog supply line. This resistor is useful for many applica-
is not necessary. The capacitor CI for the averaging tions, also for those which do not operate via cable.
control can be reduced to 100 nF.
On a PCB the forward path VCC to the laser diode
Operation of laser diode via cable
should be arranged in parallel with the return path to
It is recommended to connect a capacitor of 1 to 10 nF KLD even when the line is only a few centimeters in
across the laser diode in order to protect the laser length.
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.
ICHAUS [ IC-HAUS GMBH ]
