LM4782 datasheet(21/27 Pages) NSC

21 / 27 page

Application Information (Continued)

reduced by increasing the size of the bypass capacitor near

the IC. With at least a 20µF local bypass, these voltage

surges are important only if the lead length exceeds a couple

feet (>1µH lead inductance). Twisting together the supply

and ground leads minimizes the effect.

PHYSICAL IC MOUNTING CONSIDERATIONS

Mounting of the package to a heat sink must be done such

that there is sufficient pressure from the mounting screws to

insure good contact with the heat sink for efficient heat flow.

Over tightening the mounting screws will cause the package

to warp reducing contact area with the heat sink. Less

contact with the heat sink will increase the thermal resis-

tance from the package case to the heat sink (

CS) resulting

in higher operating die temperatures and possible unwanted

thermal shut down activation. Extreme over tightening of the

mounting screws will cause severe physical stress resulting

in cracked die and catastrophic IC failure. The recom-

mended mounting screw size is M3 with a maximum torque

of 50 N-cm. Additionally, it is best to use washers under the

screws to distribute the force over a wider area or a screw

with a wide flat head. To further distribute the mounting force

a solid mounting bar in front of the package and secured in

place with the two mounting screws may be used. Other

mounting options include a spring clip. If the package is

secured with pressure on the front of the package the maxi-

mum pressure on the molded plastic should not exceed

150N/mm

Additionally, if the mounting screws are used to force the

package into correct alignment with the heat sink, package

stress will be increased. This increase in package stress will

result in reduced contact area with the heat sink increasing

die operating temperature and possible catastrophic IC fail-

ure.

LM4782 датащи(PDF) 21 Page - National Semiconductor (TI)