THS3092_14 Datasheet, PDF (23/45 Pages) Texas Instruments – HIGH-VOLTAGE, LOW-DISTORTION, CURRENT-FEEDBACK OPERATIONAL AMPLIFIERS

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PowerPAD™ LAYOUT CONSIDERATIONS
1. PCB with a top side etch pattern as shown in
Figure 67. There should be etch for the leads as
well as etch for the thermal pad.
2. Place 13 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 THS3092/6 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
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 THS3092/6
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 13 holes exposed. The bottom-side
solder mask should cover the 13 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.
THS3092
THS3096
SLOS428B – DECEMBER 2003 – REVISED FEBRUARY 2006
POWER DISSIPATION AND THERMAL
CONSIDERATIONS
The THS3092/6 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 performance 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 calculated
using the following formula.
P _Dmax
+
T_max *
q_JA
T_A
where:
P_Dmax is the maximum power dissipation in the amplifier (W).
T_max is the absolute maximum junction temperature (°C).
T_A is the ambient temperature (°C).
θ_JA = θ_JC + θ_CA
θ_JC is the thermal coefficient from the silicon junctions to the
case (°C/W).
θ_CA is the thermal coefficient from the case to ambient air
(°C/W).
For systems where heat dissipation is more critical,
the THS3092 is offered in an 8-pin SOIC (DDA) with
PowerPAD package, and the THS3096 is offered in a
14-pin TSSOP (PWP) with PowerPAD package for
even better thermal performance. The thermal
coefficient for the PowerPAD packages are
substantially improved over the traditional SOIC.
Maximum power dissipation levels are depicted in the
graph for the available packages. The data for the
PowerPAD packages assume a board layout that
follows the PowerPAD layout guidelines referenced
above and detailed in the PowerPAD application note
(literature number SLMA002). The following graph
also illustrates the effect of not soldering the
PowerPAD to a PCB. The thermal impedance
increases substantially which may cause serious heat
and performance issues. Be sure to always solder the
PowerPAD to the PCB for optimum performance.
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