THS4281DBVT datasheet(23/31 Pages) TI

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DESIGN TOOLS

Evaluation

Fixtures

and

Application

Support

THERMAL ANALYSIS

Dmax +

Tmax–TA

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 coefficient from the silicon junctions to the

case (

°C/W).

θCA is the thermal coefficient from the case to ambient air

(

°C/W).

0.2

0.4

0.6

0.8

1.2

1.4

1.6

1.8

−40

−20

100

8-pin SOIC (D) Package

8-pin MSOP

(DGK) Package

5-pin SOT23

(DBV) Package

TA − Free-Air Temperature − °C

θJA = 97.5°C/W for 8-Pin SOIC (D)

θJA = 180.8°C/W for 8-Pin MSOP (DGK)

θJA = 255.4°C/W for 5-Pin SOT−23 (DBV)

TJ = 125°C, No Airflow

THS4281

SLOS432 – APRIL 2004

A 50-

Ω environment is normally not necessary

When determining whether or not the device satisfies

onboard, and in fact a higher impedance environ-

the maximum power dissipation requirement, it is

ment improves distortion as shown in the distor-

important to consider not only quiescent power dissi-

tion versus load plots.

pation, but also dynamic power dissipation. Often

maximum power dissipation is difficult to quantify

5. Socketing a high speed part like the THS4281

because the signal pattern is inconsistent, but an

is not recommended. The additional lead length

estimate of the RMS value can provide a reasonable

and pin-to-pin capacitance introduced by the

analysis.

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.

Information

Texas Instruments is committed to providing its cus-

tomers with the highest quality of applications sup-

The THS4281 does not incorporate automatic thermal

port. To support this goal, an evaluation board has

shutoff protection, so the designer must take care to

been developed for the THS4281 operational ampli-

ensure that the design does not violate the absolute

fier. The evaluation board is available and easy to

maximum junction temperature of the device. Failure

use allowing for straight-forward evaluation of the

may result if the absolute maximum junction tempera-

device. These evaluation board can be obtained by

ture of 150

° C is exceeded. For long-term depend-

ordering through the Texas Instruments Web site,

ability, the junction temperature should not exceed

www.ti.com, or through your local Texas Instruments

125

°C.

Sales Representative. A schematic for the evaluation

The thermal characteristics of the device are dictated

board is shown in Figure 77 with their default

by the package and the PC board. Maximum power

component values. Unpopulated footprints are shown

dissipation for a given package can be calculated

to provide insight into design flexibility.

using the following formula.

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.

Figure 76. Maximum Power Dissipation vs

Ambient Temperature

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