Datasheet

iC-NZN
N-TYPE LASER DIODE DRIVER
Rev C1, Page 8/17
DESCRIPTION OF FUNCTIONS
iC-NZN is a laser diode pulse driver. The device fea-
tures the following functions:
• Peak or averaging control
• Optical power (APC) or current control (ACC)
• Pulses of up to 155 MHz in controlled burst mode
• Laser current limitation
• Operation of blue laser diodes possible
• Error signalling for overcurrent
• Sleep mode with less than 50 µA consumption
OPTICAL POWER CONTROL
The iC-NZN supports the control of the laser diode’s
optical output power for all common laser diode pin
configurations (N, P and M). The control is enabled
with pin REGE set to high. With AVG set to low, the
peak power control is enabled. The laser power level
is selected by means of the resistor RMON (= RMD +
PMD). This control mode can be used for frequencies
up to ca. 4 Mhz. For higher frequencies the averag-
ing control (AVG = high) or the burst mode have to be
used. Tables 4 and 5 show how to set the inputs for
laser control depending on the input interface selected
(TTL or LVDS).
Laser control in TTL mode (TTL = high/open)
EP EN NSLP REGE SYN Mode
- - low/open - - Power-save mode
low/open open high - low LDA charged, laser off
high open high high/open high LDA charged, laser on, peak control
high open high low high LDA charged, laser on, burst mode
Table 4: Laser control in TTL mode
Laser control in LVDS mode (TTL = low)
EP EN NSLP REGE SYN Mode
- - low/open - - Power-save mode
< EN > EP high - low LDA charged, laser off
> EN < EP high high/open high LDA charged, laser on, peak control
> EN < EP high low high LDA charged, laser on, burst mode
Table 5: Laser control in LVDS mode
RMON dimensioning
Peak control (AVG = low): In order to calculate the right
value of RMON, the value of IM (monitor current with
respect to optical output power) of the laser diode must
be known. RMON must be chosen in a way that the
monitor current generated by the desired output power
creates a voltage drop across RMON of 500 mV (cf.
Electrical Characteristics No. 201).
Averaging control (AVG = high): In this mode the cal-
culation is the same as in peak control, only the result
has to be divided by the duty cycle of the laser pulses,
D =
τ
T
. At a duty cycle of e.g. 50% D =
1
2
. This re-
quires an external averaging capacitor of sufficient size
at pin CI though.
Control modes
Averaging Operation mode RMON calculation
AVG = 0 Peak control RMON =
V(MD)
IM
AVG = 1 Averaging control RMON =
V(MD)
IM×D
Table 6: RMON dimensioning
Example
By way of example, an output level of 1 mW is to be
set. With an optical power of 1mW e.g. laser diode
HL6339G has a typical monitor current (IM) of 15µA.
The following value is then obtained for the resistor at
pin MD (RMON = PMD + RMD, where RMD is a fixed
resistor and PMD a potentiometer.):