iC-NZP
P-TYPE LASER DIODE DRIVER
Rev A1, Page 10/13
LASER CURRENT LIMITATION
iC-NZP monitors the average laser current flowing
from pin VDDA (Figure 6). The DC current limit is set
by means of a resistor at pin RSI.
RSI @ VDD
VDDA
VDD
RSI
CVDDA
100 nF..
CVDD
100 nF..
i(RSI)x540
When dimensioning resistor RSI the following applies
(cf. Electrical Characteristics No. 106):
0.5V
RSI
VDD-0.5V
0.68..9 kΩ
0.5 V
Imax (VDDA) = 540 ×
RSI
NSLP
NERR
If no current limitation is required, pin RSI must be con-
nected to VDD to disable this feature.
Overcurrent
OverTemp.
1
Short pulses at VDDA with higher currents are possi-
ble as only the DC current is monitored and capacitor
CVDDA supplies the current for short pulses.
Figure 6: iC-NZP VDDA current limitation
BURST MODE
In controlled burst mode iC-NZP can pulse with up to pre-set operating point is maintained. To prevent the
155 MHz. Controlled here means that a pre-set oper- laser current from rising due to residual currents, the
ating point is maintained during the burst phase.
capacitor is discharged with a maximum of 150 nA (cf.
Electrical Characteristics No. 405). For a longer burst
Therefore an operating point is settled first, for which mode, an external capacitor can be connected to pin
pin REGE has to be high and the laser must be CI. As the capacitor is discharged gradually, the out-
switched on. Once the operating point has been put level must be re-settled again after a certain period,
reached the laser can be switched off again. The oper- depending on the admissible degradation of the laser
ating point is stored in an on-chip capacitor and when output power.
REGE is set to low, the burst mode is activated. The
CURRENT CONTROL
The iC-NZP also supports laser current control, when No. 406). The laser current is set by means of resis-
no monitor diode is present. For that purpose, a frac- tor RMON (= RMD + PMD). Figure 7 shows the typical
tion of the current flowing trough the laser is provided set-up for current control.
at IMON pin (ILDA / 280, cf. Electrical Characteristics
Control modes
Averaging Operation mode
RMON calculation
V(RVDD)−V(MD)
AVG = 0
AVG = 1
Peak current control RMON =
IM
V(RVDD)−V(MD)
Averaging control
RMON =
IM×D
Table 7: Current control set-up
ICHAUS [ IC-HAUS GMBH ]
