Datasheet
iC-NZN
N-TYPE LASER DIODE DRIVER
Rev C1, Page 9/17
RMON =
V(MD)
IM
=
0.5 V
15 µA
= 33.34 kΩ
External capacitor mode
In applications where an external capacitor is required
(see best performance recommendations below), the
external capacitor mode must be enabled (pin CID =
high). This connects the capacitor to the control cir-
cuit and additionally enables a pull-down current at pin
CI to prevent this capacitor from being charged due
to residual currents (cf. Electrical Characteristics No.
406).
Best performance recommendations
The operating point for the laser diode is stored in an
on-chip capacitor. This permits a fast start-up but can
lead to an unstable control circuit under certain condi-
tions such as inadequate PCB layout or laser diodes
with very low monitor current. In these cases, an op-
tional capacitor can be connected as close as possible
to the chip, across pin CI and CIS. This will prevent
instability of the control circuit. For averaging control
a 10 nF capacitor at CI is recommended. Special care
must be taken in PCB layout when laying out the path
from the laser diode’s cathode via pin LDK to AGND.
This path must be kept as short as possible to avoid
parasitic inductances. A sbubber network across the
laser diode helps to compensate for these parasitic in-
ductances.
Figures 3, 4 and 5 show the typical set-up for the dif-
ferent N, P and M-type diode configurations.
N-type diodes
EP
NSLP
EN
OUTPUT MONITOR
1
LDA
RSI
+
RSI
OUTPUT DRIVER
TTL
OverCurrent
1
..300mA
x240
VDD
AVG
..10 nF..
REGE
0.68..
CLDA
&
ECI
100 nF..
CID
Low V(LDA)
..300mA
RVDD
MD
RMD
LVDS/TTL
PMD
&
iC-NZN
CI
SYN
VDD
i(RSI)x540
100 nF..
LDA MONITOR
PMD
N
T.PAD
-
Bandgap, Reference, Overtemp
&
9kΩ
1
ECI
GND
INPUT INTERFACE
CI
VSY
&
OverTemp.
-
RGND
CIS
REF
AGND
CI
NERR
1
+
IMON
LDK
RMD
RSI
+3..+5.5V
CVDD
VDD
GND
N
Figure 3: Circuit example for N-type laser diodes
P-type diodes
Althought this kind of laser diodes are supported by iC-
NZN, it’s strongly recommended to use iC-NZP instead
since in this configuration, all the pulses at LDK will
be coupled directly to pin MD due to monitor diode’s
internal capacitance, thus making an accurate control
much more difficult. Moreover, applications with P-type
laser diode case grounded are possible with iC-NZP
only.