IC-WKN_14 Datasheet, PDF (10/12 Pages) IC-Haus GmbH – 15 V CW LASER DIODE DRIVER

iC-WKN
15 V CW LASER DIODE DRIVER
APPLICATION NOTES
Rev C1, Page 10/12
Setting the output power
The output power is simply set by
RM = ^{V (MDA)}
I(MD)
with
V(MDA) = Item-No. 101 and
I(MD) = monitor current of the laser diode at the de-
sired operating point.
RM should be combined from a fixed resistor (max.
output power) and a trimmer (calibration).
Layout
Pin AGND acts solely as a ground reference for the
power regulator (CI and RM) and must not be short-
circuited with GND externally. This could have a neg-
ative effect on the control behaviour and monitor func-
tions.
Cooling
Laser diodes should be sufficiently cooled, particularly
with the power-regulated operation of setups which
use iC-WKN, 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 con-
trol unit then compensates for by increasing the laser
current. This in turn brings about a rise in power dissi-
pation in the laser diode and thus also in temperature.
In this instance the laser diode could be damaged (re-
sulting in spottiness and an increase in operating cur-
rent) or even destroyed before the overcurrent shut-
down threshold in iC-WKN is reached.
For improved power dissipation with N-type laser
diodes the common terminal (= case) can be con-
nected to the power supply line. This eases the heat
conducting assembly into a module case, connected to
the power supply (e.g. battery powered modules). Al-
ternatively the power supply may be e.g. -5 V with the
module case grounded.
+2.4..+15 V
6
VCC
CVCC
..47 nF..
TRANSIENT
PROTECTION
iC−WKN
1
D
NQ
R
GND
0..3
1
RGND
GND
OVERCURRENT
OVERTEMP.
LDA
7
CLDA
..1 uF..
MDK
4
−
MDA
5
+
VREF
0.5 V
2
CI
LDK
8
MD LD
FEEDBACK MON.
CI
..100 nF..
RM
0.08..200 k Ω
CM
47 pF
3
AGND
Figure 3: Laser diode case connected to the power
supply
Figure 3 shows this setup with VCC and LDA short cir-
cuited. The function of the now by-passed transient
protection resistor is replaced by an external resistor
(typ. 3 Ω) in the GND line.
Current limiting
Figure 4 shows a relatively simple way to add a se-
lectable current limiter to iC-WKN. V_BE (Q_lim)/R_lim sets
the maximum current through the laser diode..
+2.4..+15 V
6
CVCC
..47 nF..
VCC
TRANSIENT
PROTECTION
iC−WKN
1
D
NQ
R
GND
1
GND
OVERCURRENT
OVERTEMP.
Verwendbare Laserdioden: N, P, M
MD LD
MD LD
LDA
7
CLDA
..1 uF..
MDK
4
−
MDA
5
+
VREF
0.5 V
2
CI
LDK
8
MD LD
Qlim
Rlim
FEEDBACK MON.
CI
..100 nF..
RM
0.08..200 k Ω
CM
47 pF
3
AGND
LD
MD
Figure 4: iC-WKN with selectable current limiter
Miscellaneous
Further application notes on the iC-WK family (iC-WK,
iC-WKL, iC-WKN) and the data sheet of the demo
board are available as separate documents.