THS4505 Datasheet, PDF (30/38 Pages) Texas Instruments – WIDEBAND, LOW-DISTORTION, FULLY DIFFERENTIAL AMPLIFIERS

THS4504
THS4505
SLOS363C – AUGUST 2002 – REVISED MARCH 2004
pad on the underside of the package [see Fig-
ure 93(c)]. Because this thermal pad has direct
thermal contact with the die, excellent thermal per-
formance can be achieved by providing a good
thermal path away from the thermal pad.
The PowerPAD package allows for both assembly
and thermal management in one manufacturing oper-
ation. During the surface-mount solder operation
(when the leads are being soldered), the thermal pad
can also be soldered to a copper area underneath the
package. Through the use of thermal paths within this
copper area, heat can be conducted away from the
package into either a ground plane or other heat
dissipating device.
The PowerPAD package represents a breakthrough
in combining the small area and ease of assembly of
surface mount with the, heretofore, awkward mechan-
ical methods of heatsinking.
DIE
Side View (a)
DIE
End View (b)
Thermal
Pad
Bottom View (c)
Figure 93. Views of Thermally Enhanced Package
Although there are many ways to properly heatsink
the PowerPAD package, the following steps illustrate
the recommended approach.
Pin 1
0.205
0.060
0.013
0.017
0.030
0.075
0.025 0.094
0.010
vias
0.035
Top View
0.040
Figure 94. View of Thermally Enhanced Package
PowerPAD PCB LAYOUT CONSIDERATIONS
1. Prepare the PCB with a top side etch pattern as
shown in Figure 94. There should be etch for the
leads as well as etch for the thermal pad.
2. Place five holes in the area of the thermal pad.
These holes should be 13 mils in diameter. Keep
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them small so that solder wicking through the
holes is not a problem during reflow.
3. Additional vias may be placed anywhere along
the thermal plane outside of the thermal pad
area. This helps dissipate the heat generated by
the THS4500 family IC. These additional vias
may be larger than the 13-mil diameter vias
directly under the thermal pad. They can be
larger because they are not in the thermal pad
area to be soldered so that wicking is not a
problem.
4. Connect all holes to the internal ground plane.
5. When connecting these holes to the ground
plane, do not use the typical web or spoke via
connection methodology. Web connections have
a high thermal resistance connection that is
useful for slowing the heat transfer during
soldering operations. This makes the soldering of
vias that have plane connections easier. In this
application, however, low thermal resistance is
desired for the most efficient heat transfer. There-
fore, the holes under the THS4500 family
PowerPAD package should make their connec-
tion to the internal ground plane with a complete
connection around the entire circumference of the
plated-through hole.
6. The top-side solder mask should leave the ter-
minals of the package and the thermal pad area
with its five holes exposed. The bottom-side
solder mask should cover the five holes of the
thermal pad area. This prevents solder from
being pulled away from the thermal pad area
during the reflow process.
7. Apply solder paste to the exposed thermal pad
area and all of the IC terminals.
8. With these preparatory steps in place, the IC is
simply placed in position and run through the
solder reflow operation as any standard sur-
face-mount component. This results in a part that
is properly installed.
POWER DISSIPATION AND THERMAL
CONSIDERATIONS
The THS4500 family of devices does not incorporate
automatic thermal shutoff protection, so the designer
must take care to ensure that the design does not
violate the absolute maximum junction temperature of
the device. Failure may result if the absolute maxi-
mum junction temperature of 150°C is exceeded. For
best performance, design for a maximum junction
temperature of 125°C. Between 125°C and 150°C,
damage does not occur, but the performance of the
amplifier begins to degrade.
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