LMH6525 Datasheet, PDF (14/15 Pages) National Semiconductor (TI) – Four-hannel Laser Diode Driver with Dual Output

Application Hints (Continued)
that the unused pins on the part can also be used to connect
a copper pour area to the Die Attach Pad. Figure 5 Heat
Sinking (with the same orientation as the first layout ex-
ample) shows using the unused pin to provide a thermal path
to copper pour heat sinks. In this layout the analog ground
has been separated from the power ground so pin 7 is not
connected to the Die Attach Paddle even though it would
help remove heat from the part. The above layout is based
on a single-sided circuit board. If a dual-sided circuit board
was used there would also be vias on the Die Attach Pad
that would conduct heat to a copper plane on the bottom side
of the board.
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FIGURE 4. Decoupling Capacitors
OSCILLATOR RESISTORS
The resistors and/or potentiometers used to set oscillator
frequency or amplitude should be as close to the part as
possible. If the grounds are split when using a single-sided
flex circuit, it is essential that these resistors and potentiom-
eters share the same ground as the GNDA pin and decou-
pling capacitor.
THERMAL
As mentioned previously, the primary way to get heat out of
the LLP package is by the large Die Attach Pad at the center
of the part’s underside. On two-layer circuits this can be
done with vias. On single-sided circuits the pad should con-
nect with a copper pour to either the GND pin or, if a better
thermal path can be achieved, with the V_DD pins. Be aware
FIGURE 5. Heat Sinking
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