Datasheet

iC-WJB
2.7 V LASER DIODE DRIVER
Rev E1, Page 6/12
APPLICATIONS INFORMATION
Laser Power Adjustment
The iC-WJB device can be adapted to CW laser diodes
of up to 40 mW. When the supply voltage is higher than
approx. 4.5 V, LD models in common cathode configu-
ration can be used.
The pin ISET is used for the adjustment to the sensi-
tivity of the monitor diode and to set the desired optical
laser power. The setpoint for the averaging control of
the monitor diode current is pre-set at this pin.
+5V
AMD
CI CWD GND
VCC
IN
ISET
KLD
MD
LD
24kΩ
RSET
2
1
REF
VCC
REF
3 1
4
3
iC−WJB
C1
47uF
470nF
CI
0..2Ω
R1
2nF
C3
4
6
2
3 1
7
8
5
REFERENCE
WATCHDOG
THERMAL
POWER DOWN
INPUT
DRIVER STAGE
SHUTDOWN
Figure 1: Circuit diagram for LD models with a common cathode
To calculate the current required at ISET, the average
optical laser power is to determine:
P
av
= P
peak
∗
t
whi
T
with peak value P
peak
and pulse/period duration t
whi
/T.
twhi
T
Ppeak
twlo
Figure 2: Duty cycle
Example for CW operation
P
cw
= 1 mW (pin IN at VCC, pin CWD open), laser
diode maximum optical output of 3mW, monitor diode
with 0.75 mA at 3 mW.
At P
av
= P
cw
= 1 mW, the monitor diode current is
0.25 mA and RSET is calculated to:
RSET =
CR1∗ V(ISET)
I
av
(AMD)
=
3∗ 1.22V
0.25mA
= 14.64kΩ
with Electrical Characteristics No. 301 for V(ISET) and
No. 107 for current ratio CR1.
Example for pulse operation
Pulse duty factor t
whi
/T set to 20 % at P
peak
= 3 mW,
laser diode as above with maximum optical output of
3 mW, monitor diode with 0.75 mA at 3 mW.
The average optical power is set to 0.6 mW by the
pulse duty factor; the average monitor diode current
I
AV
is then 0.15 mA. The resistor RSET is calculated
to: