THS3120_16 Datasheet, PDF (21/35 Pages) Texas Instruments – LOW-NOISE, HIGH-OUTPUT DRIVE, CURRENT-FEEDBACK OPERATIONAL AMPLIFIERS

THS3120
THS3121
www.ti.com........................................................................................................................................ SLOS420E – SEPTEMBER 2003 – REVISED OCTOBER 2009
PowerPAD DESIGN CONSIDERATIONS
The THS3120 and THS3121 are 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 59a and Figure 59b). This arrangement results
in the lead frame being exposed as a thermal pad on
the underside of the package (see Figure 59c).
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. Note that devices such as the
THS312x have no electrical connection between the
PowerPAD and the die.
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 59. Views of Thermally-Enhanced Package
Although there are many ways to properly heatsink
the PowerPAD package, the following steps illustrate
the recommended approach.
PowerPAD LAYOUT CONSIDERATIONS
1. PCB with a top side etch pattern as shown in
Figure 60. 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 0.01 inch (0,254 mm) in
diameter. Keep them small so that solder wicking
through the holes is not a problem during reflow.
0.205
(5,21)
0.060
(1,52)
0.013
(0,33)
0.075
(1,91)
0.030
(0,76)
0.010
(0,254)
vias
0.035
(0,89)
0.017
(0,432)
0.094
(2,39)
0.025
(0,64)
0.040
(1,01)
Dimensions are in inches (millimeters).
Figure 60. DGN PowerPAD PCB Etch and Via
Pattern
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 THS3120/THS3121 IC. These additional vias
may be larger than the 0.01-inch (0,254 mm)
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.
Note that the PowerPAD is electrically isolated
from the silicon and all leads. Connecting the
PowerPAD to any potential voltage such as V_S–,
is acceptable as there is no electrical connection
to the silicon.
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
THS3120/THS3121 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.
Copyright © 2003–2009, Texas Instruments Incorporated
Product Folder Link(s): THS3120 THS3121
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