THS4281 Datasheet, PDF (23/31 Pages) Texas Instruments – VERY LOW-POWER, HIGH-SPEED, RAIL-TO-RAIL INPUT AND OUTPUT VOLTAGE-FEEDBACK OPERATIONAL AMPLIFIER

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A 50-Ω environment is normally not necessary
onboard, and in fact a higher impedance environ-
ment improves distortion as shown in the distor-
tion versus load plots.
5. Socketing a high speed part like the THS4281
is not recommended. The additional lead length
and pin-to-pin capacitance introduced by the
socket can create a troublesome parasitic net-
work which can make it almost impossible to
achieve a smooth, stable frequency response.
Best results are obtained by soldering the
THS4281 onto the board.
THERMAL ANALYSIS
The THS4281 does not incorporate automatic thermal
shutoff protection, so 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 tempera-
ture of 150° C is exceeded. For long-term depend-
ability, the junction temperature should not exceed
125°C.
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–T_A
q_JA
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).
1.8
1.6
8-pin SOIC (D) Package
1.4
8-pin MSOP
1.2
(DGK) Package
1
0.8
0.6
0.4
5-pin SOT23
0.2
(DBV) Package
0
−40 −20 0 20 40 60 80 100
T_A − Free-Air Temperature − °C
θ_JA = 97.5°C/W for 8-Pin SOIC (D)
θ_JA = 180.8°C/W for 8-Pin MSOP (DGK)
θ_JA = 255.4°C/W for 5-Pin SOT−23 (DBV)
T_J = 125°C, No Airflow
Figure 76. Maximum Power Dissipation vs
Ambient Temperature
THS4281
SLOS432 – APRIL 2004
When determining whether or not the device satisfies
the maximum power dissipation requirement, it is
important to consider not only quiescent power dissi-
pation, but also dynamic power dissipation. Often
maximum power dissipation is difficult to quantify
because the signal pattern is inconsistent, but an
estimate of the RMS value can provide a reasonable
analysis.
DESIGN TOOLS
Evaluation Fixtures and Application Support
Information
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 THS4281 operational ampli-
fier. The evaluation board is available and easy to
use allowing for straight-forward evaluation of the
device. These evaluation board can be obtained by
ordering through the Texas Instruments Web site,
www.ti.com, or through your local Texas Instruments
Sales Representative. A schematic for the evaluation
board is shown in Figure 77 with their default
component values. Unpopulated footprints are shown
to provide insight into design flexibility.
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 THS4281 device is available through either
the Texas Instruments Web site (www.ti.com) or as
one model on a disk from the Texas Instruments
Product Information Center (1–800–548–6132). The
PIC is also available for design assistance and
detailed product information at this number. These
models do a good job of predicting 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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