iC-VJ, iC-VJZ
LASER DIODE CONTROLLER
Rev A1, Page 7/10
Oscillator
PRF [1V/div]
The internal oscillator operates in the range approx.
10 kHz to 4 MHz. This enables laser pulse repetition
frequencies from 1 to 200 kHz. Fig. 2 shows the pulse
repetition frequency as a function of the oscillator cir-
cuit.
LASER Output
[2mW/div]
I(KDL) [50mA/div]
KDL [1V/div]
Timebase = 1:s/div
Example
R1 = 620 Ω, C1 = 82 pF: f ≈ 200 kHz
Figure 3: Settled control with 200 kHz pulse repeti-
tion frequency
f [kHz]
200
Turn-on and Turn-off Behavior
Capacitor C2 also determines the starting time from
switching on the supply voltage VCC to steady-state
laser pulse operation. The values of C2 which are
necessary higher for low pulse repetition frequencies
increase this starting time to several milliseconds (Fig.
4). The following applies for estimating the starting
time:
100
C1= 82pF
C1= 220pF
C1= 1nF
1
2
3
4
5
6
7
8
R1 [kΩ]
Figure 2: Pulse repetition frequency
Averaging Control
2.5V ∗C2 2.5V ∗C2∗RSET
Ton
≈
=
I(ISET)
1.22V
The control of the average optical laser power requires
the external capacitor C2 at pin CI. This capacitor is
used for averaging and must be adjusted to the se-
lected pulse repetition frequency and the charging cur-
rent preset with RSET. The ratios are linear in both
cases, i.e. C2 must be increased in size proportionally
as the pulse repetition frequency slows or resistance
RSET decreases.
Example
C2 = 4.7 µF, RSET = 10 kΩ: Ton ≈ 96 ms
VCC [2V/div]
PRF [2V/div]
LASER Output [2mW/div]
440∗I(ISET)
f ∗V(ISET)
440
f ∗RSET
C
[1V/div]
C2 ≥
=
Timebase
= 20 ms/div
Figure 4: Turn-on behavior f = 10 kHz, RSET =
Example
10 kΩ, C2 = 4.7 µF
Frequency 10 kHz, RSET = 10 kΩ: C2 ≈ 4.7 µF
LASER Output
Otherwise the charging of C2 during the pulse pauses
(with I(ISET) = 1.22 V / RSET) will result in excessive
mean value potential at pin CI and the laser diode may
be destroyed with the next pulse. C2 is correctly di-
mensioned when the current through the laser diode
and the optical output signal do not show any over-
shooting on the rising edge.
LASER Output [1mW/div]
C
[200mV/div]
Figure 5: Setteling of the averaging control
In steady-state condition, signals will then appear at
the IC pins as shown in Fig. 3. In this case the laser
pulse exhibits a minimal overshoot on the rising edge, For high pulse repetition frequencies (200 kHz) and low
but this can be tolerated. The increase in the current in C2 values (220 nF) and for RSET = 10 kΩ the aver-
KLD and the laser pulse follow directly after the signal aging control achieves its operating point after 3.5 ms.
at the divider output PRF. The outputs PRF and NPRF Fig. 5 shows the turn-on, Fig. 6 the turn-off behavior,
are used for receiver synchronisation.
here in case of undervoltage.
ICHAUS [ IC-HAUS GMBH ]
