THS4631 Datasheet, PDF (16/34 Pages) Texas Instruments – HIGH-VOLTAGE, HIGH SLEW RATE, WIDEBAND FET-INPUT OPERATIONAL AMPLIFIER

THS4631
SLOS451B – DECEMBER 2004 – REVISED AUGUST 2011
soldered so that wicking is not a problem.
4. Connect all holes to the internal ground plane.
Although the PowerPAD is electrically isolated
from all pins and the active circuitry, connection
to the ground plane is recommended. This is due
to the fact that ground planes on most PCBs are
typically the targets copper area. Offering the
best thermal path heat to flow out of the device.
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 THS4631
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 via holes exposed. The bottom-side
solder mask should cover the via 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.
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
amplifier begins to degrade. 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 Equation 9.
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P_{D max} +
T_max * T_A
q_JA
(9)
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).
NOTE:
For systems where heat dissipation is more
critical, the THS4631 is offered in an 8-pin MSOP
with PowerPAD package and an 8-pin SOIC with
PowerPAD package with better thermal
performance. The thermal coefficient for the
PowerPAD packages are substantially improved
over the traditional SOIC. Maximum power
dissipation levels are depicted in Figure 46 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
number SLMA002. Figure 46 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.
4
T_J = 125°C
3.5
3
θJ_A = 58.4°C/W
2.5
θJ_A = 98°C/W
2
1.5
1
0.5
θJ_A = 158°C/W
0
−40 −20 0 20 40 60 80 100
T_A − Free-Air Temperature − °C
Figure 46. Maximum Power Dissipation
vs. Ambient Temperature
16
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