iC-NZN
N-TYPE LASER DIODE DRIVER
Rev B1, Page 11/17
LASER CURRENT LIMITATION
LDA current limitation
RSI @ VDD
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.
LDA
VDD
RSI
CLDA
CVDD
100 nF..
i(RSI)x540
100 nF..
0.5V
When dimensioning resistor RSI the following applies
(cf. Electrical Characteristics No. 106):
RSI
VDD-0.5V
0.68..9 kΩ
0.5 V
Imax (LDA) = 540 ×
RSI
The current limitation can be disabled by connecting
pin RSI to VDD.
NSLP
NERR
Overcurrent
OverTemp.
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.
1
LDK current limitation
Figure 6: iC-NZN LDA 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):
iC-NZN features two different current limitations, limit-
ing the average current flowing from pin LDA plus the
current flowing into pin LDK.
0.5 V
Imax (LDK) = 520 ×
RSI
BURST MODE
In controlled burst mode iC-NZN can pulse with up to For a longer burst mode, an external capacitor can
155 MHz. Controlled here means that a pre-set oper- be connected to pin CI. To prevent the laser current
ating point is maintained during the burst phase.
from rising due to residual currents, the capacitor is
discharged then with a maximum of 150 nA (cf. Elec-
Therefore an operating point is settled first, for which trical Characteristics No. 406). As the capacitor is dis-
pin REGE has to be high and the laser diode must charged gradually, the output level must be re-settled
be switched on. Once the operating point has been again after a certain period, depending on the admis-
reached the laser diode can be switched off again. The sible degradation of the laser output power.
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.
ICHAUS [ IC-HAUS GMBH ]
