IC-NZP_14 Datasheet, PDF (9/15 Pages) IC-Haus GmbH – P-TYPE LASER DIODE DRIVER

iC-NZP
P-TYPE LASER DIODE DRIVER
Control modes
Averaging Operation mode
AVG = 0 Peak control
AVG = 1 Averaging control
RMON calculation
RMON
=
V (MD)
IM
RMON
=
V (MD)
IM ×D
Table 6: RMON dimensioning
Rev C1, Page 9/15
Example
By way of example, an output level of 1 mW is to be
set. With an optical power of 1 mW e.g. laser diode
HL6342G has a typical monitor current (IM) of 15 µA.
The following value is then obtained for the resistor at
pin MD (RMON = PMD + RMD, where RMD is a fixed
resistor and PMD a potentiometer.):
RMON = ^{V (MD)} = ^{0.25 V} = 16.67 k Ω
IM
15 µA
External capacitor mode
In applications where an external capacitor is required
(see best performance recommendations below), the
external capacitor mode must be enabled (pin NCID =
low).
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 with very
low monitor current. In that cases, an external capaci-
tor is to 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 ca-
pacitor at CI is recommended. Special care must be
taken in PCB layout when laying out the path from the
laser diode’s cathode to GND. This path must be kept
as short as possible to avoid parasitic inductances. A
snubber network across the laser diode also helps to
compensate for these parasitic inductances.
Figures 3, 4 and 5 show the typical set-up for the dif-
ferent P, N and M-type diode configurations.
P-Type diodes
+3..+5.5V
CVDD
100 nF..
RSI
0.68.. 9kΩ
GND
VDD
RSI
NSLP
REGE
i(RSI)x540
LDA MONITOR
VD D
AVG
&
VSY
SYN
EP
EN
TTL
NCID
LVDS/TTL
+
-
VD D
VD D
NERR
T.PAD
GND
INPUT INTERFACE
OverTemp.
1
OverCurrent
Low V(LDA)
RVDD
VDDA
iC-NZP
VDDL
&
1
-
REF
+
ECI
CIS
ECI
x280
CI
LDA
IMON
MD
OUTPUT DRIVER
CVDDA
100 nF..
..10 nF..
CI
PMD
RMD
..300mA
P
Bandgap, Reference, Overtemp
OUTPUT MONITOR
RGND
Figure 3: Circuit example for P-type laser diodes (case grounded)