IC-WJBEVALWJ1D ICHAUS [IC-Haus GmbH], IC-WJBEVALWJ1D Datasheet - Page 8

• Manufacturer Part Number: IC-WJBEVALWJ1D
• Description: 2.7 V LASER DIODE DRIVER
• Manufacturer: ICHAUS [IC-Haus GmbH]

laser pulses indicate that the undervoltage detector is
active.
Watchdog
The watchdog ensures that the capacitor CI is dis-
charged during protracted pulses at IN. During the
pulse pauses the voltage at CI increases by
ure 3).
The discharge of capacitor CI by the watchdog protects
the laser diode from being destroyed by an excessive
turn-on current during the next pulse.
The capacitor CWD should be dimensioned such that
the response time t
than the pulse pause t
sult, the watchdog is just short of being activated.
For response times t
with t
No. 407, 408.
iC-WJB
2.7 V LASER DIODE DRIVER
2.55 V
2.45 V
Figure 6: Turn-on behaviour, detailed view f(IN) =
5.0 V
3.0 V
Figure 7: Turn-off behaviour, f(IN) = 100 kHz (1:1),
0 V
0 V
0 A
0 A
pmin
100 kHz (1:1), CI = 470 nF, RSET = 10 k
CI = 470 nF, RSET = 10 k
and K
VCC
wd
CWD =
V =
p
p
of the watchdog is slightly longer
from Electrical Characteristics
longer than t
wlo
I(ISET ) t
I(KLD)
of the input signal. As a re-
V(CI)
t
p
CI
K
wd
t
V(CI)
pmin
wlo
pmin
I(KLD)
applies:
V (Fig-
Time
Time
Figure 8 shows the signals during normal operation,
without the watchdog being activated. The potential at
CWD rises during pulse pauses but does not reach the
watchdog activation threshold.
Figure 9 shows the watchdog behaviour when the in-
put frequency is reduced from 100 kHz to 10 kHz. The
pulse pauses are longer than the watchdog’s response
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)
tics 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.
300 uA
Figure 8: Watchdog, CWD open, f(IN) = 100 kHz
300 uA
Figure 9: Watchdog, CWD open, f(IN) = 100 kHz
5.0 V
5.0 V
3.0 V
2.0 V
5.0 V
0 A
0 V
0 V
0 A
0 V
5 V
0 V
3 V
2 V
V(CWD)
(1:1), CI = 470 nF, RSET = 10 k
10 kHz (1:1), CI = 470 nF, RSET = 10 k
V(CWD)
I(AMD)
V(IN)
V(CI)
V(IN)
I(AMD)
wd
V(CI)
(Electrical Characteris-
Rev E1, Page 8/12
Time
Time