IC-VJ Datasheet, PDF (7/10 Pages) IC-Haus GmbH – LASER DIODE CONTROLLER

iC-VJ, iC-VJZ
LASER DIODE CONTROLLER
Rev A1, Page 7/10
Oscillator
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.
Example
R1 = 620 Ω, C1 = 82 pF: f ≈ 200 kHz
f [kHz]
200
100
C1= 82pF
C1= 220pF
C1= 1nF
1
2
3
4
5
6
7
8
R1 [kΩ]
PRF [1V/div]
LASER Output
[2mW/div]
I(KDL) [50mA/div]
KDL [1V/div]
Timebase = 1:s/div
Figure 3: Settled control with 200 kHz pulse repeti-
tion frequency
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:
Figure 2: Pulse repetition frequency
Averaging Control
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.
C2 ≥ ^{440 ∗ I(ISET )} = ⁴⁴⁰
f ∗ V (ISET ) f ∗ RSET
Example
Frequency 10 kHz, RSET = 10 kΩ: C2 ≈ 4.7 µF
2.5 V ∗ C2 2.5 V ∗ C2 ∗ RSET
T_on ≈ _{I(ISET )} =
1.22 V
Example
C2 = 4.7 µF, RSET = 10 kΩ: T_on ≈ 96 ms
VCC [2V/div]
PRF [2V/div]
LASER Output [2mW/div]
C [1V/div]
Timebase = 20 ms/div
Figure 4: Turn-on behavior f = 10 kHz, RSET =
10 kΩ, C2 = 4.7 µF
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.
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,
but this can be tolerated. The increase in the current in
KLD and the laser pulse follow directly after the signal
at the divider output PRF. The outputs PRF and NPRF
are used for receiver synchronisation.
LASER Output
LASER Output [1mW/div]
C [200mV/div]
Figure 5: Setteling of the averaging control
For high pulse repetition frequencies (200 kHz) and low
C2 values (220 nF) and for RSET = 10 kΩ the aver-
aging control achieves its operating point after 3.5 ms.
Fig. 5 shows the turn-on, Fig. 6 the turn-off behavior,
here in case of undervoltage.