iC-NZN
N-TYPE LASER DIODE DRIVER
Rev B1, Page 12/17
CURRENT CONTROL
The iC-NZN also supports laser current control, when teristics No. 407). Tables 7 and 8 show how to set the
no monitor diode is present. For that purpose, a frac- inputs for laser control depending on the input interface
tion of the current flowing trough the laser diode is pro- selected (TTL or LVDS).
vided at IMON pin (ILDK / 240, cf. Electrical Charac-
Laser control in TTL mode (TTL = high/open)
EP
EN
NSLP
AVG REGE
SYN Mode
-
-
low/open -
-
-
-
Power save mode
low/open open high
high open high
-
low LDA charged, laser off
high high/open high LDA charged, laser on, regulated
Table 7: Laser control in TTL mode
Laser control in LVDS mode (TTL = Low)
EP
EN
NSLP
AVG REGE
SYN Mode
-
-
low/open -
-
-
-
Power save mode
< EN > EP high
> EN < EP high
-
low LDA charged, laser off
high high/open high LDA charged, laser on, regulated
Table 8: Laser control in LVDS mode
The laser current is set by means of resistor RMON Best performance recommendations
(= RMD + PMD). The operating point for the laser diode is stored in
an on-chip capacitor. This permits a fast start-up but
can make the regulated system unstable under cer-
tain conditions such as inadequate PCB layout. In
these cases, an optional capacitor can be connected
as close as possible to the chip, across pins CI and
CIS.
V(RVDD) − V(MD)
RMON =
IMON
Figure 7 shows the typical set-up for current control.
External capacitor mode
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 possi-
ble to avoid parasitic inductances. A snubber network
across the laser diode also helps to compensate for
these parasitic inductances.
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).
ICHAUS [ IC-HAUS GMBH ]
