Wavelength Electronics WHS302, Datasheet And Operating Manual

Page: 15 / 28

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WLD SERIES LASER DIODE DRIVERS
UTILIZING V
SET
(PIN 2)
Pin 2 on the WLD3343, V
SET
, can be used for externally
defining the setpoint, or as a modulation input. Figure 12
illustrates a typical configuration of the voltage input.
!
The available voltage range for V
SET
is 0-2 V.
Connecting voltages outside this range can
result in damage to the WLD3343 or the
laser diode.
GND
7
WLD3343
2
V
SET
2 k
Ω
1 k Ω
DC BIAS
TRIMPOT
2.5 V
Bandgap
Voltage
Reference
V
PIN2
V
DD
OR OR
+
Figure 12. Configuring the voltage input for either a fixed
(left) or a modulated (right) voltage setpoint.
For a given voltage supplied to V
SET
, either the laser
diode current will change (Constant Current mode), or the
photodiode current will change (Constant Power mode).
Constant Current Mode:
The resulting laser diode current is given by Equation (9) .
I
LD
=
V
PIN2
(9)
2·R
SENSE
Constant Power Mode:
The resulting photodiode current is given by
Equation (10)
.
I
PD
=
V
PIN2 (10)
2·R
PD
MONITORING THE LASER DIODE CURRENT
(PIN 3)
Pin 3 (IMON) produces a voltage proportional to the current
flowing through the laser diode. Equation (11) provides a
transfer function for converting the voltage output of Pin 3 to
the amount of forward current.
I
LD
=
V
PIN3
(11)
2·R
SENSE
MONITORING THE PHOTODIODE CURRENT
The photodiode current is measured differently in
Constant Current and Constant Power mode, due to the
configurational differences between the modes.
Constant Current Mode:
In Constant Current mode, the photodiode current is
measured directly across R
PD
. Equation (12) provides
a transfer function for converting this voltage into the
corresponding current through the monitor photodiode.
I
PD
=
V
RPD (12)
R
PD
Constant Power Mode:
In Constant Power mode, the photodiode current is
measured using Pin 4 (PMON). Equation (13) provides a
transfer function for converting this voltage to the amount of
current flowing through the monitor photodiode.
I
PD
=
V
PIN4 (13)
2·R
PD
Use the online WLD Circuit Calculator to automatically determine
values for external components.
www.teamwavelength.com/support/design-tools/wld-calculator/