THS3120 Datasheet, PDF (22/28 Pages) Texas Instruments – LOW-NOISE, HIGH-OUTPUT DRIVE, CURRENT-FEEDBACK, OPERATIONAL AMPLIFIERS

THS3120, THS3121
SLOS420A – SEPTEMBER 2003 – REVISED NOVEMBER 2003
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 coeffiecient from the silicon junctions to
the case (°C/W).
θ_CA is the thermal coeffiecient from the case to ambient
air (°C/W).
For systems where heat dissipation is more critical,
the THS3120 and THS3121 are offered in an 8-pin
MSOP with PowerPAD package offering 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.
4
Τ_J = 125°C
3.5
3
θ_JA = 58.4°C/W
2.5
2
θ_JA = 95°C/W
1.5
1
0.5
0
−40
θ_JA = 158°C/W
−20 0 20
40 60
80 100
T_A − Free-Air Temperature − °C
Results are With No Air Flow and PCB Size = 3”x 3”
θJ_A = 58.4°C/W for 8-Pin MSOP w/PowerPad (DGN)
θJ_A = 95°C/W for 8-Pin SOIC High−K Test PCB (D)
θJ_A = 158°C/W for 8-Pin MSOP w/PowerPad w/o Solder
Figure 59. Maximum Power Distribution vs
Ambient Temperature
www.ti.com
When determining whether or not the device satisfies
the maximum power dissipation requirement, it is
important to not only consider quiescent power dissi-
pation,
but
also
dynamic
power
dissipation. Often times, this is difficult to quantify
because the signal pattern is inconsistent, but an
estimate of the RMS power dissipation can provide
visibility into a possible problem.
DESIGN TOOLS
Evaluation Fixtures, Spice Models, and
Application Support
Texas Instruments is committed to providing its cus-
tomers with the highest quality of applications sup-
port. To support this goal an evaluation board has
been developed for the THS3120 and THS3121
operational amplifier. The board is easy to use,
allowing for straightforward evaluation of the device.
The evaluation board can be ordered through the
Texas Instruments web site, www.ti.com, or through
your local Texas Instruments sales representative.
Computer simulation of circuit performance using
SPICE is often useful when analyzing the perform-
ance of analog circuits and systems. This is particu-
larly true for video and RF-amplifier circuits where
parasitic capacitance and inductance can have a
major effect on circuit performance. A SPICE model
for the THS3121 is available through the Texas
Instruments web site (www.ti.com). The PIC is also
available for design assistance and detailed product
information. These models do a good job of pre-
dicting small-signal ac and transient performance
under a wide variety of operating conditions. They are
not intended to model the distortion characteristics of
the amplifier, nor do they attempt to distinguish
between the package types in their small-signal ac
performance. Detailed information about what is and
is not modeled is contained in the model file itself.
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