IC-WKM_15 Datasheet, PDF (10/12 Pages) IC-Haus GmbH – M-TYPE CW LASER DIODE DRIVER

iC-WKM
M-TYPE CW LASER DIODE DRIVER
APPLICATION NOTES
Rev C2, Page 10/12
Laser diode types
In principle, all three laser diode types can be operated
by iC-WKM.
higher than that of red laser diodes, for example, due
to the higher forward voltage.
As iC-WKM has been optimised for use with M-type
laser diodes, it is with this type of diode that the best
functionality is achieved. This type of setup also en-
ables the laser diode package to be connected to GND.
With P-type laser diodes it is also possible to connect
the laser diode package to GND. Here, however, the
current mirror at MDK introduces a certain error to the
automatic power control (c.f. Electrical Characteristics
Nos. 108, 110).
Even N-type laser diodes can be operated by iC-WKM;
iC-WKN, however, which has been optimised for use
with these diodes, may be a better choice.
Figure 3: Operation of an M-type laser diode
Layout
To prevent instability of the regulator an additional ca-
pacitor (ca. 100 pF) must be positioned directly at the
iC’s pin CI. Depending on the laser diode, capacitor
CM with typ. 2 nF in parallel to RM may be required for
stability.
Pin AGND acts solely as a ground reference for the
power regulator (CI and RM) and should not be short-cir-
cuited with GND externally. This could have a negative
effect on the control behavior and monitor functions.
Cooling
Laser diodes should be sufficiently cooled, particularly
with the power-regulated operation of setups which use
iC-WKM, for example. The power dissipation in the
laser diode otherwise causes the diode to heat up and
the level of efficiency to drop which the power control
unit then compensates for by increasing the laser cur-
rent. This in turn brings about a rise in power dissipation
in the laser diode and thus also in temperature. In this
instance the laser diode could be damaged (resulting in
spottiness and an increase in operating current) or even
destroyed before the overcurrent shutdown threshold
in iC-WKM is reached. This applies in particular to blue
laser diodes whose power dissipation is considerably
Figure 4: Operation of a P-type laser diode
Figure 5: Operation of an N-type laser diode