IC-WJ Datasheet, PDF (8/12 Pages) IC-Haus GmbH – LASER DIODE DRIVER

iC-WJ, iC-WJZ
LASER DIODE DRIVER
Rev C1, Page 8/12
Example
CI = 470 nF, RSET = 10 kΩ: T_on = 9.6 ms
Figure 6 shows a detailed view of the start of laser op-
eration; Figure 7 shows the shut-down behavior. The
decline in the voltage at CI and the absence of the
laser pulses are signs that the undervoltage detector
is active.
2.55 V
2.45 V
V(CI)
I(KLD)
The capacitor CWD should be dimensioned such that
the response time t_p of the watchdog is slightly longer
than the pulse pause t_wlo of the input signal. As a re-
sult, the watchdog is just short of being activated.
For response times t_p longer than t_pmin applies:
CWD = ^{tp − tpmin}
K_wd
with t_pmin and K_wd from Electrical Characteristics
No. 407, 408.
V(IN)
5.0 V
0A
Time
Figure 6: Turn-on behavior, detailed view f(IN) =
100 kHz (1:1), CI = 470 nF, RSET = 10 kΩ
5.0 V
0V
3.0 V
VCC
V(CI)
0V
0V
5V
0V
3V
2V
300 uA
V(CWD)
V(CI)
I(AMD)
0A
Time
Figure 8: Watchdog, CWD open, f(IN) = 100 kHz
(1:1), CI = 470 nF, RSET = 10 kΩ
I(KLD)
0A
Time
Figure 7: Turn-off behavior, f(IN) = 100 kHz (1:1), CI
= 470 nF, RSET = 10 kΩ
Watchdog
In order for the watchdog to function correctly, the input
IN must be activated with a CMOS output (e.g. with an
HCMOS gate: see Figure 1).
The watchdog ensures that the capacitor CI is dis-
charged during protracted pulse pulses at IN. During
the pulse pauses the potential at CI increases by ∆V
(Figure 3):
5.0 V
V(IN)
0V
5.0 V
V(CWD)
0V
3.0 V
V(CI)
2.0 V
300 uA
I(AMD)
0A
Time
Figure 9: Watchdog, CWD open, f(IN) = 100 kHz →
10 kHz (1:1), CI = 470 nF, RSET = 10 kΩ
∆V = ^{I(ISET ) ∗ twlo}
CI
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.
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.
Figure 9 shows the watchdog behavior when the in-
put frequency is reduced from 100 kHz to 10 kHz. The
pulse pauses are longer than the watchdog’s response