IC-NZN_14 Datasheet, PDF (11/17 Pages) IC-Haus GmbH – N-TYPE LASER DIODE DRIVER

iC-NZN
N-TYPE LASER DIODE DRIVER
LASER CURRENT LIMITATION
Rev C1, Page 11/17
CVDD
100 nF..
RSI
0.68..9 kΩ
VDD
RSI
RSI @ VDD
i(RSI)x540
0.5V
VDD-0.5V
LDA
CLDA
100 nF..
NSLP
NERR
Overcurrent
1
OverTemp.
Figure 6: iC-NZN LDA current limitation
iC-NZN features two different current limitations, limit-
ing the average current flowing from pin LDA plus the
current flowing into pin LDK.
LDA current limitation
iC-NZN monitors the average laser current flowing
from pin LDA (Figure 6). The DC current limit is set
by means of a resistor at pin RSI.
When dimensioning resistor RSI the following applies
(cf. Electrical Characteristics No. 106):
0.5 V
I_max (LDA) = 540 × _RSI
Short pulses at LDA with higher currents are possi-
ble as only the DC current is monitored and capacitor
CLDA supplies the current for short pulses.
LDK current limitation
The control circuit also monitors the laser current in pin
LDK and limits this current when reaching the thresh-
old also defined by RSI. The following applies (cf. Elec-
trical Characteristics No. 107):
0.5 V
I_max (LDK ) = 700 × _RSI
BURST MODE
In controlled burst mode iC-NZN can pulse with up to
155 MHz. Controlled here means that a pre-set oper-
ating point is maintained during the burst phase.
Therefore an operating point is settled first, for which
pin REGE has to be high and the laser diode must
be switched on. Once the operating point has been
reached the laser diode can be switched off again. The
operating point is stored in an on-chip capacitor and
when pin REGE is set to low, the burst mode is acti-
vated. The pre-set operating point is maintained.
For a longer burst mode, an external capacitor can
be connected to pin CI. To prevent the laser current
from rising due to residual currents, the capacitor is
discharged then with a maximum of 2.6 µA (cf. Electri-
cal Characteristics No. 406). As the capacitor is dis-
charged gradually, the output level must be re-settled
again after a certain period, depending on the admis-
sible degradation of the laser output power.