4.0
0
3.5
3.0
2.5
2.0
1.5
1.0
0.5
P
MaximumP
owerDissipation
W
-
D
-
T =+125 C
°
J
q
=58.4
JA
°
C/W
q
=95
JA
°
C/W
q
=158
JA
°
C/W
-
40
100
-
20
0
20
40
60
80
T
Free-AirTemperature
A
-
- °
C
P
Dmax
+
Tmax * TA
q
JA
where:
PDmax is the maximum power dissipation in the amplifier (W).
Tmax is the absolute maximum junction temperature (°C).
TA is the ambient temperature (°C).
θJA = θJC + θCA
θJC is the thermal coeffiecient from the silicon junctions to
the case (
°C/W).
θCA is the thermal coeffiecient from the case to ambient
air (
°C/W).
SLOS420E – SEPTEMBER 2003 – REVISED OCTOBER 2009........................................................................................................................................ www.ti.com
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
The THS3120 and THS3121 incorporate 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
Results are with no air flow and PCB size = 3 inches × 3 inches
performance and reliability, the designer must take
(76,2 mm × 76,2 mm);
θJA = 58.4°C/W for MSOP-8 with
PowerPAD (DGN);
θJA = 95°C/W for SOIC-8 High-K test PCB (D);
care to ensure that the design does not exceed a
θJA = 158°C/W for MSOP-8 with PowerPAD without solder.
junction temperature of +125°C. Between +125°C
and +150°C, damage does not occur, but the
Figure 61. Maximum Power Distribution vs
performance of the amplifier begins to degrade and
Ambient Temperature
long
term
reliability
suffers.
The
thermal
characteristics of the device are dictated by the
When determining whether or not the device satisfies
package
and
the
PC
board.
Maximum
power
the maximum power dissipation requirement, it is
dissipation for a given package can be calculated
important to not only consider quiescent power
using the following formula.
dissipation, 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
customers with the highest quality of applications
support. To support this goal an evaluation board has
(1)
been developed for the THS3120 and THS3121
operational amplifier. The board is easy to use,
For systems where heat dissipation is more critical,
allowing for straightforward evaluation of the device.
the THS3120 and THS3121 are offered in an
The evaluation board can be ordered through the
MSOP-8 with PowerPAD package offering even
better thermal performance. The thermal coefficient
your local Texas Instruments sales representative.
for
the
PowerPAD
packages
are
substantially
improved over the traditional SOIC. Maximum power
Computer simulation of circuit performance using
dissipation levels are depicted in the graph for the
SPICE
is
often
useful
when
analyzing
the
available packages. The data for the PowerPAD
performance of analog circuits and systems. This is
packages assume a board layout that follows the
particularly true for video and RF-amplifier circuits
PowerPAD layout guidelines referenced above and
where parasitic capacitance and inductance can have
detailed in the PowerPAD application note (literature
a major effect on circuit performance. A SPICE model
number
SLMA002). also illustrates the effect of not
for the THS3121 is available through the Texas
soldering the PowerPAD to a PCB. The thermal
impedance increases substantially which may cause
information center (PIC) is also available for design
serious heat and performance issues. Be sure to
assistance and detailed product information. These
always solder the PowerPAD to the PCB for optimum
models do a good job of predicting small-signal ac
performance.
and transient performance under a wide variety of
operating conditions. They are not intended to model
22
Copyright 2003–2009, Texas Instruments Incorporated