THS4509_14 Datasheet, PDF (31/43 Pages) Texas Instruments – WIDEBAND, LOW-NOISE, LOW-DISTORTION, FULLY-DIFFERENTIAL AMPLIFIER

THS4509
www.ti.com
PowerPAD PCB LAYOUT
CONSIDERATIONS
Although there are many ways to properly heatsink
the PowerPAD package, the following steps illustrate
the recommended approach.
0.144
0.049
Pin 1
0.0095
0.015
0.144
0.012
0.0195 0.0705
0.032
0.010
vias
0.0245
Top View
0.030
Figure 93. PowerPAD PCB Etch and Via Pattern
1. Prepare the PCB with a top side etch pattern as
shown in Figure 93. 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.
The holes should be 13 mils (0.013 in, 0,33 mm)
in diameter. Keep 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. They help dissipate the heat generated by
the 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
SLOS454H – JANUARY 2005 – REVISED NOVEMBER 2009
useful for slowing the heat transfer during
soldering operations. This resistance 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 IC
PowerPAD package should make the 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 configuration 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 process results
in a part that is properly installed.
The next consideration is the package constraints.
The two sources of heat within an amplifier are
quiescent power and output power. The designer
should never forget about the quiescent heat
generated within the device, especially multi-amplifier
devices. Because these devices have linear output
stages (Class AB), most of the heat dissipation is at
low output voltages with high output currents.
The other key factor when dealing with power
dissipation is how the devices are mounted on the
PCB. The PowerPAD devices are extremely useful
for heat dissipation. But the device should always be
soldered to a copper plane to fully use the heat
dissipation properties of the PowerPAD. The SOIC
package, on the other hand, is highly dependent on
how it is mounted on the PCB. As more trace and
copper area is placed around the device, θ_JA
decreases and the heat dissipation capability
increases. For a single package, the sum of the RMS
output currents and voltages should be used to
choose the proper package.
Copyright © 2005–2009, Texas Instruments Incorporated
Product Folder Link(s): THS4509
Submit Documentation Feedback
31