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Analog Technologies
ALDD28V15A401
Digital High Voltage Constant Current 15A Laser Driver
Minimizing the Output Noise
The laser driver has extremely low output noise; care must
be taken in using this laser driver to achieve this lower noise
performance. One of the noise sources is the beating
frequency interference from other power mode electronics,
such as another laser driver, TEC (Thermo-Electric Cooler)
controller, or power supply. There are 2 ways to avoid the
frequency beating: set the switching frequencies of other
electronics to be far away from the switching frequency of
the laser driver, 500kHz.
The driver can be turned on and off by setting the SBDN pin
high and low respectively. It is recommended to turn the
driver on by this sequence:
To turn on: turn on the power by providing the power supply
voltage to the driver on VPS pin, turn on the driver by
releasing the SBDN pin.
To turn off: turn off the driver by lowering the voltage of
SDN pin, turn off the power by stopping the voltage supply
on the VPS pin.
When not controlled by the SBDN pin: leave it unconnected
and turn the driver on and off by the power supply.
Adjusting the Output Current
The output current is set by adjusting W1, which sets input
voltages of LISL and LISH, pin 6 and 7. See Figure 6. The
output current will be:
I
OUT
(A) = 3.662
×
V
LIS
LIS can also be set by using a DAC to replace the W1 in
Figure 6. Make sure that the DAC has low output noise.
Monitoring the Output Current
The output current of the driver can be monitored by
measuring the voltage on the LIO pin. This feature is very
useful for a micro-driver based system where the ADC is
available and monitoring of the current in real time is
required. This pin provides a very low noise voltage signal
and is proportional to the output current:
I
OUT
(A) =3.662
×
V
LIO
(A).
For example, when the output signal is 4.096V, the output
current is 15A.
LIO can be used to drive an ADC directly, and also be
measured by a multi-meter.
First Time Power Up
Laser diode is a highly valuable asset yet, a delicate device.
Faults in connections and damages done to the driver during
soldering process may damage the laser diode permanently.
To protect the laser diode, it is highly recommend to use 3 to
18 regular diodes which is > 15A to form a “dummy laser”
and insert it in the place of the real laser diode, when
powering up the driver for the first time.
Use an oscilloscope to monitor the LDA voltage at times of
powering up and enabling the shutdown pin and powering
down the laser driver and turning off the shutdown pin, and
make sure that there is no over-shoot output voltage at the
LDA pin. At the same time, it uses an ammeter in series with
the dummy laser, to make sure that the output current is
correct. After thoroughly checking and making sure the
system is free of faults, disconnect the dummy laser diode
and connect the real laser diode in place. The driver output
voltage range for the laser is between 0 to V
VPS
(power
supply input voltage).
