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.
3
REF
DRIVER STAGE
1
VCC
5
C1
47uF
+5V
REFERENCE
C3
2nF
4
RSET
24kΩ
INPUT
2
VCC
REF
LD
MD
ISET
THERMAL
SHUTDOWN
KLD
8
R1
0..2Ω
POWER DOWN
7
AMD
6
IN
4
1
3
WATCHDOG
iC−WJB
CI
GND
3
CI
470nF
1
CWD
2
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
At P
av
= P
cw
= 1 mW, the monitor diode current is
0.25 mA and RSET is calculated to:
with peak value P
peak
and pulse/period duration t
whi
/T.
twhi
twlo
Ppeak
RSET
=
CR1
∗
V
(ISET ) 3
∗
1.22
V
=
= 14.64
k
Ω
I
av
(AMD)
0.25
mA
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:
T
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 3 mW, monitor diode
with 0.75 mA at 3 mW.
ICHAUS [ IC-HAUS GMBH ]
