IC-NZ Datasheet, PDF (12/20 Pages) IC-Haus GmbH – FAIL-SAFE LASER DIODE DRIVER

iC-NZ
FAIL-SAFE LASER DIODE DRIVER
Rev B2, Page 12/20
Demo-Board
When using an N-type laser diode jumper J2 must be
placed between pins 2 and 3 on the demo board. If
a P-type laser diode is used the jumper must be con-
nected between pins 1 and 2.
Warning!
Following calibration pin EN has to be briefly set to low
before actual operation may start with EN set to high
again. The following explains why.
When the low channel (LENL → hi) is switched on ca-
pacitor CIL is charged. When the middle channel is
switched in the internal control unit switches to CIM
and starts to charge it. The voltage at CIL is then no
longer regulated. As residual current could boost the
voltage at CIL, which in turn would increase the cur-
rent in the low channel, thus the capacitor at CIL is
actively discharged with a maximum of 100 nA. The
current in the low channel slowly decreases. As the
control unit endeavours to keep the optical power con-
stant, the capacitor at CIM is charged at the same rate
as CIL is gradually discharged. If the middle chan-
nel is now switched off, the control unit switches back
to the low channel. Capacitor CIL is regulated again;
CIM, however, remains charged. If the middle channel
were then again to be switched on, far too much cur-
rent would flow; this could destroy the laser diode. The
same happens if the low and middle channels are reg-
ulated and the high channel switched on for a lengthy
period of time. In this instance CIL and CIM are slowly
discharged and the voltage at CIH rises in order to
maintain a constant optical power. The entire process
is illustrated in Figure 7.
EN
CIL
CIM
LENL
LENM
I(Laser)
Overcurent
Figure 7: Behavior with very long power-on times
OPERATION WITH ONE OR TWO CHANNELS
It is of course also possible to operate iC-NZ with one
or two levels of light intensity. To make use of the safety
functions of the system in one- or two-channel mode,
pins LDKx (x: L, M) on the unused channels must be
kept unconnected. Nodes CIx should be directly short-
circuited with AGND. To use the safety functions of the
safety monitor diode the high channel must always be
in use in one- or two-channel mode. Figures 8 to 11
give the configuration of iC-NZ for one- or two-channel
operation for both N- and P-type laser diodes.