THS4503-EP_17 Datasheet, PDF (30/40 Pages) Texas Instruments – WIDEBAND, LOW-DISTORTION FULLY DIFFERENTIAL AMPLIFIERS

THS4503−EP
SGLS291A − APRIL 2005 − JANUARY 2012
PowerPAD DESIGN CONSIDERATIONS
The THS4500 family is available in a thermally-enhanced
PowerPAD family of packages. These packages are
constructed using a downset leadframe upon which the die
is mounted [see Figure 112(a) and Figure 112(b)]. This
arrangement results in the lead frame being exposed as a
thermal pad on the underside of the package [see
Figure 112(c)]. Because this thermal pad has direct
thermal contact with the die, excellent thermal
performance 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 operation.
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 mechanical methods
of heatsinking.
DIE
Side View (a)
DIE
End View (b)
Thermal
Pad
Bottom View (c)
Figure 112. 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 113. PowerPAD PCB Etch and Via Pattern
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PowerPAD PCB LAYOUT CONSIDERATIONS
1. Prepare the PCB with a top side etch pattern as shown
in Figure 113. 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 the holes
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. Therefore, the holes under the THS4500
family PowerPAD package should make their
connection 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 terminals
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 surface-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 maximum 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.