© 2017
www.teamWavelength.com
15
FL591FL LASER DIODE DRIVER
1.0
2.0
3.0
4.0
5.0
6.0
7.0
8.0
9.0
0.00
0.05
0.10
0.15
0.20
0.25
Voltage (V)
Current (A)
V
DROP
V
S
I
MAX
Load Lin
e
Figure 8. Example SOA Chart, FL591FL Laser Driver
1.0
2.0
3.0
4.0
5.0
6.0
7.0
8.0
9.0
0.00
0.05
0.10
0.15
0.20
0.25
Voltage (V)
Current (A)
Figure 9. SOA Chart,
FL591FL Operating as a 250 mA Driver
3.0
4.0
5.0
6.0
7.0
8.0
9.0
0.00
0.05
0.10
0.15
0.20
0.25
0.30
0.35
0.40
0.45
0.50
Voltage (V)
Current (A)
Figure 10. SOA Chart,
FL591FL Operating as a 500 mA Driver
SAFE OPERATING AREA CALCULATION
Before attempting to operate the FL591FL, it is imperative
that you first determine that the FL500 driver will operate
within the
Safe Operating Area
(SOA). Consult the
instructions for calculating the FL500 Safe Operating Area
online at:
http://www.teamwavelength.com/support/calculator/soa/soald.php
If you have any questions about the Safe Operating Area
calculator, call the factory for free and prompt technical
assistance.
!
I
t
Is
ImperatIve
that
you
verIfy
the
unIt
wIll
operate
wIthIn
the
Internal
heat
dIssIpatIon
s
afe
o
peratIng
a
rea
(soa).
o
peratIng
the
controller
outsIde
the
soa
may
damage
or
destroy
the
fl591fl
and
/
or
loads
.
We recommend using the online SOA calculators rather
than the charts provided here. The online calculators take
into consideration operating temperature.
Follow these steps to use the SOA Chart to determine if the
FL591FL will be operating safely. Refer to the example SOA
chart in
Figure 8
. Room temperature SOA charts for the
FL591FL are shown in
Figure 9
and
Figure 10.
• Determine the V
S
supply voltage for the laser driver. For
this example assume V
S
= 8 VDC.
• Refer to the laser datasheet to find the voltage (V
F
) at
the required drive current, and maximum current (I
MAX
)
specifications. For this example, assume V
F
= 1.8 V and
I
MAX
= 200 mA.
• Calculate the voltage drop across the controller:
V
DROP
= V
S
– V
F
• Mark V
DROP
on the X-axis, and extend a line upward
• Mark I
MAX
on the Y-axis, and extend a line to the right
until it intersects the V
DROP
line
• On the X-axis, mark the supply voltage (V
S
)
• Extend a diagonal line from V
S
to the intersection of the
V
DROP
and I
MAX
lines; this is the Load Line
• If the Load Line crosses the Safe Operating Area line at
any point, the configuration is not safe
If the SOA calculator indicates the FL591FL will be outside
of the Safe Operating Area, the system must be changed
so that less power is dissipated within the driver. See
AN-LDTC01: The Principle of the Safe
for information on shifting the Load Line.
After changing any of the parameters, recalculate the
SOA to make sure the controller will operate safely. If you
have questions, or run into difficulties calculating the SOA,
contact Wavelength Electronics for assistance.
