IC-HK_1 Datasheet, PDF (9/13 Pages) IC-Haus GmbH – 155MHz LASER SWITCH

iC-HK
155MHz LASER SWITCH
Rev 21.11.01, Page 9/13
Laser current limitation without an iC-WK shutdown
Another way of providing protection against overcurrent is illustrated in Figure 19. With increasing current
through RK1 transistor Q1 is switched on, lowering the voltage at CI and thus reducing the laser current without
triggering iC-WK‘s overcurrent shutdown.
VCC
LDA
TRANSIENT
PROTECTION
1
D
NQ
R
-
+
iC-WK
MDK
MDA
VREF
0.5V
CI
LDK
OVERCURRENT
FEEDBACKMON./
OVERTEMP.
GND
AGND
LDK
VDD
CI
EN1
EN2
AGND1
AGND2 GND
Fig. 19: Laser current limitation without an iC-WK shutdown
Caution: Due to the direct feedback of the controlled current through RKx to the control voltage at CI there is a
certain tendency towards oscillation. This can be counteracted by experimenting with the settings of the
components involved.
Hint: Please bear in mind that the laser characteristic
of most laser diodes has a strong temperature
dependency, in particular with regard to threshold
current (I_th) and efficiency. To avoid damage to the
laser diode sufficient cooling has to be provided
and/or protection against overcurrent implemented as
shown above.
Fig. 20: Temperature dependency of the laser
bias