LMH6584 Datasheet, PDF (17/20 Pages) National Semiconductor (TI) – 32x16 400 MHz Analog Crosspoint Switches, Gain of 1, Gain of 2

maximum heat dissipation, a smaller heat sink can be select-
ed if forced air circulation will be used. With natural convection
the heat sink will reduce the θ_JA from 22°C/W to approximately
11°C/W. Using a fan will increase the effectiveness of the heat
sink considerably by reducing θ_JA to approximately 5°C/W.
When doing thermal design it is important to note that every-
thing from board layout to case material and case venting will
impact the actual θ_JA of the total system. The θ_JA specified in
the datasheet is for a typical board layout with external case
enclosing the board.
PRINTED CIRCUIT LAYOUT
Generally, a good high frequency layout will keep power sup-
ply and ground traces away from the input and output pins.
Parasitic capacitances on these nodes to ground will cause
frequency response peaking and possible circuit oscillations
(see Application Note OA-15 for more information). If digital
control lines must cross analog signal lines (particularly in-
puts) it is best if they cross perpendicularly. National Semi-
conductor suggests the following evaluation boards as a
guide for high frequency layout and as an aid in device testing
and characterization National Semiconductor offers an eval-
uation board which can be found on the LMH6584 and
LMH6585 Product Folder.
30045053
FIGURE 6. Maximum Dissipation vs. Ambient
Temperature
17
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