© 2020
14
PLD10000/PLD12500 LASER DIODE DRIVER
CHANGE THE ANALOG INPUT MODULATION
TRANSFER FUNCTION
The Analog Input Modulation transfer function can be
changed by adding a voltage divider resistor network
external to the PLD driver.
circuit.
R2
ANALOG
INPUT
V
Keep R1 and R2 below 100 k
Ω
for maximum accuracy.
IN
R1
R2 + R1
R2
New
Transfer
Function
Built-In Transfer Function
=
*
Example:
(for PLD10000)
R1 = 9 k
Ω
R2 = 1 k
Ω
1 + 9
1
New
Transfer
Function
2.3 A / V = 0.23 A / V
=
*
16
19
COMMON
Figure 13. Changing the Analog Input
Modulation Transfer Function
EXTERNAL SETPOINT CIRCUIT
An external trimpot circuit can be used to adjust the laser
R1
R2
D1
Analog Input
Pin 16
V
+5V
Common
Pin 19
= Supply voltage
D1 = Bandgap reference* (LM4040)
R1 = 2.2 kΩ, 1 W resistor
R2 = Trimpot, 10 kΩ to 100 kΩ
* must be at least 1 volt greater than
the voltage value of D1.
V
+5V
V
+5V
Pin 13, 14, 15
Figure 14. Trimpot Circuit for Analog Input
IMPORTANT INFORMATION ON GROUNDING
Some laser diodes connect the laser anode or cathode to
the case. Pay particular attention to grounding to ensure
safe operation of the PLD and laser.
!
i
t
is
critical
that
the
PlD
Driver
is
ProPerly
grounDeD
. i
F
the
PlD
Driver
is
useD
with
a
w
avelength
e
lectronics
temPerature
controller
,
you
may
neeD
to
use
two
seParate
Power
suPPlies
that
Float
inDePenDently
oF
each
other
.
If the laser anode is connected to the laser case, it is possible
that the anode will be connected to earth ground when
the laser is installed in a benchtop mount, or in your laser
system. In situations where the laser diode is connected to
the case, it is critical that the negative terminal of the power
supply remain isolated from earth ground.
FINE TUNE DEEP MODULATION
If the analog modulation input is near the rail (> 4.5 V), output
current signal response may be insufficient. Performance
may be improved by connecting a low-ESR 330 µF,
16 V, electrolytic capacitor between pins 10 and 13. This
decoupling capacitor should be connected at the driver.
CABLE LENGTHS AND HIGH CURRENT
The length and gauge of cable from the power supply or
to the laser diode can impact performance. The resistance
and inductance of the wire can reduce bandwidth or cause
the voltage to the PLD to droop.
Use minimum 14 AWG wire for the laser diode interconnect
wires. Always twist the wire pairs to eliminate reactance.
If the output current starts to oscillate as setpoint voltage
approaches the limit setting, then the power supply cables
may be too long. If you cannot shorten the cables, place a
330 µF capacitor across pins 10 and 13 to minimize droop.
