IC-WJB Datasheet, PDF (6/12 Pages) IC-Haus GmbH – 2.7 V LASER DIODE DRIVER

iC-WJB
2.7 V LASER DIODE DRIVER
APPLICATIONS INFORMATION
Rev E1, Page 6/12
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.
REFERENCE
3
REF
RSET
24kΩ
4 _ISET
INPUT
2
6 _IN
THERMAL
SHUTDOWN
VCC
POWER DOWN
REF
4
DRIVER STAGE
VCC ⁵
C1
47uF
+5V
1
C3
LD
2nF
MD
KLD ⁸
R1
0..2Ω
1
3
AMD ⁷
CWD
2
WATCHDOG
CI
CI
470nF
iC−WJB
GND
3
1
Figure 1: Circuit diagram for LD models with a common cathode
To calculate the current required at ISET, the average At P_av = P_cw = 1 mW, the monitor diode current is
optical laser power is to determine:
0.25 mA and RSET is calculated to:
P_av
=
P_peak
∗
t_whi
T
with peak value P_peak and pulse/period duration t_whi/T.
CR1 ∗ V (ISET ) 3 ∗ 1.22 V
RSET =
=
= 14.64 k Ω
I_av (AMD)
0.25 mA
twhi
twlo
T
Figure 2: Duty cycle
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.
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.
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: