THS3120 Datasheet, PDF (21/28 Pages) Texas Instruments – LOW-NOISE, HIGH-OUTPUT DRIVE, CURRENT-FEEDBACK, OPERATIONAL AMPLIFIERS

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Pin 1
0.030
0.075
0.205
0.060
0.013
0.017
0.025 0.094
0.010
vias
0.035
0.040
Top View
Figure 58. DGN PowerPAD PCB Etch and Via
Pattern
PowerPAD™ LAYOUT CONSIDERATIONS
1. PCB with a top side etch pattern as shown in
Figure 58. 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 10 mils 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. This helps dissipate the heat generated by
the THS3120 / THS3121 IC. These additional
vias may be larger than the 10-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.
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
THS3120, THS3121
SLOS420A – SEPTEMBER 2003 – REVISED NOVEMBER 2003
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 THS3120 / THS3121
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 THS3120 and THS3121 incorporates automatic
thermal shutoff protection. This protection circuitry
shuts down the amplifier if the junction temperature
exceeds approximately 160°C. When the junction
temperature reduces to approximately 140°C, the
amplifier turns on again. But, for maximum perform-
ance and reliability, the designer must take care to
ensure that the design does not exeed a junction
temperature of 125°C. Between 125°C and 150°C,
damage does not occur, but the performance of the
amplifier begins to degrade and long term reliability
suffers. The thermal characteristics of the device are
dictated by the package and the PC board. Maximum
power dissipation for a given package can be calcu-
lated using the following formula.
21