OPTION 2: OPERATE IN PARALLEL AS ONE
DRIVER
Use only one power supply to power Pins 4 & 6 (VSET1 &
VSET2) with ground at Pin 5 (GND). Wire the test load (laser
diode) to Pins 7 & 8 (LDC2), Pins 11 & 12 (LDC1), and to
Pin 1 (VDD). The FL500 contains circuitry for two 250 mA
drivers. They can be run in parallel to deliver 500 mA to one
laser diode (see
OPTION 1: Operate as two independent
drivers
for single channel output current of 250 mA setup).
Tie LDC1 & LDC2 together. VSET1 and VSET2 can be
tied together or one can be used to set a DC bias while the
other is used for an additive modulation signal. Only one V
S
can be used. The transfer function for tied VSET(1 & 2) is
0.25 A / V.
The RESET minimum current is 20 µA, and the leakage
current is 2 mA. Note that if VSETs are tied together, input
impedance becomes two 2 kΩ in parallel or 1 kΩ. The FL500
has a known leakage current when disabled equal to the
following magnitude:
I
OUT(LEAK)
=
V
IN
20 kΩ
This is well below 1 mA, and usual leakage expected is
100 µA.
See
for typical operating schematic.
Figure 8. Parallel Operation as One Driver
OPTION 3: OPERATE MULTIPLE FL500S IN
PARALLEL
Tie LDC1 & LDC2 (Pins 7 & 8, 11 & 12) on each FL500
together and wire the test load to these pins and Pin 1
(VDD). Tie PGND (Pins 9 & 10) together and use to ground
V
S
. Ground Pin 2 as well. Tie each Pin 3 (RESET) together
and ground to enable current to the load. Tie each VSETs
(Pins 4 & 6) together and wire the other power supply to
these pins with ground at Pins 5 (both grounded).
Multiple FL500s can be used in parallel for 1 A, 1.5 A, etc.
operation: Note input impedance on VSET drops. For two
FL500s configured for 500 mA each and used in parallel, the
input impedance drops to 500 Ω.
See
for typical operating schematic.
Figure 9. Multiple Units in Parallel Operation
STEP 4 - RESET / ENABLE FUNCTION [PIN3]
Ground Pin 3 to enable output current to the laser diode.
This control pin is common to both sources. When active,
this pin attenuates the output current amplitude to near zero
(~10 µA when configured for 250 mA max and ~20 µA if
drivers are paralleled to produce 500 mA). Current still flows
through the laser diode. The pin is active LO.
LO = LD current flowing to setpoint.
FLOAT or HI = LD current attenuated.
The input is TTL compatible.
BROWN OUT PROTECTION
If V
DD
drops below 2.7 V, the RESET circuit is triggered
immediately (on the order of 100 µsec), reducing current
through the laser diode to attenuated levels (~10 µA).
© 2020
9
FL500 LASER DIODE DRIVER
