iC-NZN
N-TYPE LASER DIODE DRIVER
Rev A1, Page 8/16
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 small 300 pF capacitor across
the laser diode helps to compensate for these parasitic
inductances.
V(MD)
IM
0.5 V
15 µA
RMON =
=
= 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 Figures 3, 4 and 5 show the typical set-up for the dif-
on-chip capacitor. This permits a fast start-up but can ferent N, P and M-type diode configurations.
N-type diodes
RVDD
+3..+5.5V
LDA
VDD
RSI
i(RSI)x540
CLDA
CVDD
100 nF..
LDA MONITOR
iC-NZN
IMON
LDK
RSI
NSLP
REGE
100 nF..
N
VDD
0.68..9kΩ
&
..300mA
1
AVG
&
VSY
SYN
+
CI
x240
REF
CI
..10 nF..
-
LVDS/TTL
CIS
EP
ECI
+
-
EN
VDD
AGND
TTL
CID
MD
ECI
OUTPUT DRIVER
INPUT INTERFACE
OverTemp.
NERR
RMD
PMD
OverCurrent
Low V(LDA)
1
Bandgap, Reference, Overtemp
OUTPUT MONITOR
T.PAD
GND
GND
RGND
Figure 3: Circuit example for N-type laser diodes
internal capacitance, thus making an accurate control
P-type diodes
Althought this kind of laser diodes are supported by iC- much more difficult. Moreover, applications with P-type
NZN, it’s strongly recommended to use iC-NZP instead laser diode case grounded are possible with iC-NZP
since in this configuration, all the pulses at LDK will only.
be coupled directly to pin MD due to monitor diode’s
ICHAUS [ IC-HAUS GMBH ]
