THS3122 Datasheet, PDF (24/43 Pages) Texas Instruments – LOW-NOISE, HIGH-SPEED, 450 mA CURRENT FEEDBACK AMPLIFIERS

THS3122, THS3125
SLOS382E – SEPTEMBER 2001 – REVISED MAY 2015
Layout Guidelines (continued)
10.1.3 PowerPAD Layout Considerations
Pin 1
0.205
(5,21)
0.060
(1,52)
0.013
(0,33)
0.017
(0,432)
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0.075
(1,91)
0.030
(0,76)
0.094
(2,39)
0.025
(0,64)
0.010
(0,254)
vias
0.035
(0,89)
0.040
(1,01)
Top View
Dimensions are in inches (millimeters).
Figure 49. DGN PowerPAD PCB Etch and Via Pattern
Although there are many ways to properly heatsink the PowerPAD package, the following steps illustrate the
recommended approach.
1. PCB with a top side etch pattern as shown in Figure 49.
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.
3. Additional vias may be placed anywhere along the thermal plane outside of the thermal pad area. These vias
help dissipate the heat generated by the THS3125/THS3122 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 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 THS3125/THS3122 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 procedure results in a part that is properly
installed.
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