© 2001, 2003, 2009
WLD3393
PAGE 6
WLD3393-00400-A Rev F
STEP 4: ATTACH THE HEATSINK AND FAN (optional for less than +5V, 200mA operation)
HEATSINK REQUIREMENTS.
The WLD3343 is designed to handle currents as high as 2.2A. The
WLD3393 demo board, however, limits output current to 2.0A. Attach a heatsink (such as WHS302
with thermal washer WTW002) to the WLD3343 when driving currents higher than 500mA. Attach a
fan (such as WXC303 (+5VDC) or WXC304 (+12VDC)) to the heatsink for output currents exceeding
1.0A. If using Wavelength accessories, refer to the WHS302, WTW002, WXC303, and / or the
WXC304 datasheets for assembly instructions.
FAN CONNECTIONS.
Connect the fan leads to the (+) and (-) fan terminal positions on the terminal
block and secure with a small fl at head screwdriver. The fan connects to the V
DD
supply, not V
S
, so care
must be exercised to ensure that the proper fan is selected, 5VDC or +12VDC, when using
dual power supplies. Optionally, for lower noise operation, the fan leads may be connected directly to
a separate power supply compatible with the fan.
STEP 5: ATTACH THE V
DD
AND V
S
POWER SUPPLIES
The WLD3393 has two power supply connections, V
S
and V
DD
. V
S
provides power for driving the
laser (minimum current capacity greater than limit current setting). V
DD
provides power to the control
electronics (minimum 100mA). V
DD
can range from +5 to +12V. V
S
can range from +4.5 to +12V. For
simple operation tie V
DD
to V
S
.
Use PGND for the power return. The common (COM) terminal on the
WLD3393 is not intended to act as a power connection, but as the low noise ground reference for
connecting an external VSET source, and for monitoring the IMON, PMON, and PDM signals.
A separate V
S
power supply allows the output current stage to operate below the minimum 5V required
for the control electronics or up to the +12V maximum (for multiple laser diodes in series). Select V
S
approximately 2.0 volts above the maximum voltage drop across the laser diode to reduce the power
dissipation in the WLD3343 component and minimize your heatsinking requirements. Note that for
type C laser diodes in Constant Power mode V
DD
must be greater than or equal to V
S
to keep the pho-
todiode signal in range.
NOISE REDUCTION.
For better performance, to reduce noise in the control electronics, it is
recommended to connect V
DD
and V
S
together at the power supply, running separate wires for V
DD
and
V
S
. Grounding the heatspreader also can reduce noise. With WLD3393 Rev. B, the screw threads
contact a grounded PEM on the board; no ground strap is necessary.
CONFIGURING THE DEMO BOARD
WLD3393 Rev A
WLD3393 Rev B
Figure 7: Grounding the heatspreader for noise reduction
