iC-NZP
P-TYPE LASER DIODE DRIVER
nar y
limi
pre
Rev B1, Page 9/15
Control modes
Averaging Operation mode RMON calculation
AVG = 0
AVG = 1
Peak control
RMON
=
Averaging control
RMON
=
Table 6: RMON dimensioning
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.):
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.
V
(MD)
IM
V
(MD)
IM×D
RMON
=
0.25
V
V
(MD)
=
= 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).
P-Type diodes
RVDD
+3..+5.5V
VDD
RSI
i(RSI)x540
LDA MONITOR
VDDA
CVDD
100 nF..
RSI
0.68.. 9kΩ
NSLP
VDD
iC-NZP
&
1
ECI
CVDDA
100 nF..
VDDL
REGE
CIS
PMD
..10 nF..
CI
RMD
AVG
VSY
SYN
EP
EN
VDD
&
LVDS/TTL
+
-
REF
-
+
x280
CI
LDA
IMON
MD
TTL
VDD
..300mA
NCID
INPUT INTERFACE
NERR
OverTemp.
1
OverCurrent
Low V(LDA)
ECI
OUTPUT DRIVER
P
Bandgap, Reference, Overtemp
OUTPUT MONITOR
RGND
GND
T.PAD
GND
Figure 3: Circuit example for P-type laser diodes (case grounded)
ICHAUS [ IC-HAUS GMBH ]
