Datasheet

P
D max
+
T
max
* T
A
q
JA
4
3.5
3
2.5
2
1.5
1
0.5
0
−40 −20 0 20 40 60 80 100
− Maximum Power Dissipation − W
P
D
T
A
− Free-Air Temperature − °C
θJ
A
= 58.4°C/W
θJ
A
= 98°C/W
θJ
A
= 158°C/W
T
J
= 125°C
THS4631
SLOS451B –DECEMBER 2004–REVISED AUGUST 2011 www.ti.com
soldered so that wicking is not a problem.
4. Connect all holes to the internal ground plane.
(9)
Although the PowerPAD is electrically isolated
where:
from all pins and the active circuitry, connection
to the ground plane is recommended. This is due
P
Dmax
is the maximum power dissipation in the
to the fact that ground planes on most PCBs are
amplifier (W).
typically the targets copper area. Offering the
T
max
is the absolute maximum junction
best thermal path heat to flow out of the device.
temperature (°C).
5. When connecting these holes to the ground
T
A
is the ambient temperature (°C).
plane, do not use the typical web or spoke via
θ
JA
= θ
JC
+ θ
CA
connection methodology. Web connections have
θ
JC
is the thermal coefficient from the silicon
a high thermal resistance connection that is
junctions to the case (°C/W).
useful for slowing the heat transfer during
θ
CA
is the thermal coefficient from the case to
soldering operations. This makes the soldering of
ambient air (°C/W).
vias that have plane connections easier. In this
application, however, low thermal resistance is
NOTE:
desired for the most efficient heat transfer.
For systems where heat dissipation is more
Therefore, the holes under the THS4631
critical, the THS4631 is offered in an 8-pin MSOP
PowerPAD package should make their
with PowerPAD package and an 8-pin SOIC with
connection to the internal ground plane with a
PowerPAD package with better thermal
complete connection around the entire
performance. The thermal coefficient for the
circumference of the plated-through hole.
PowerPAD packages are substantially improved
6. The top-side solder mask should leave the
over the traditional SOIC. Maximum power
terminals of the package and the thermal pad
dissipation levels are depicted in Figure 46 for the
area with its via holes exposed. The bottom-side
available packages. The data for the PowerPAD
solder mask should cover the via holes of the
packages assume a board layout that follows the
thermal pad area. This prevents solder from
PowerPAD layout guidelines referenced above
being pulled away from the thermal pad area
and detailed in the PowerPAD application note
during the reflow process.
number SLMA002. Figure 46 also illustrates the
7. Apply solder paste to the exposed thermal pad
effect of not soldering the PowerPAD to a PCB.
area and all of the IC terminals.
The thermal impedance increases substantially
which may cause serious heat and performance
8. With these preparatory steps in place, the IC is
issues. Be sure to always solder the PowerPAD
simply placed in position and run through the
to the PCB for optimum performance.
solder reflow operation as any standard
surface-mount component. This results in a part
that is properly installed.
POWER DISSIPATION AND THERMAL
CONSIDERATIONS
To maintain maximum output capabilities, the
THS4631 does not incorporate automatic thermal
shutoff protection. The designer must take care to
ensure that the design does not violate the absolute
maximum junction temperature of the device. Failure
may result if the absolute maximum junction
temperature of 150°C is exceeded. For best
performance, design for a maximum junction
temperature of 125°C. Between 125°C and 150°C,
damage does not occur, but the performance of the
Figure 46. Maximum Power Dissipation
amplifier begins to degrade. The thermal
vs. Ambient Temperature
characteristics of the device are dictated by the
package and the PC board. Maximum power
dissipation for a given package can be calculated
using Equation 9.
16 Copyright © 2004–2011, Texas Instruments Incorporated