Datasheet

Location of Exposed

ThermalPadon

PWPPackage

MinimumRecommended

HeatsinkArea

TPS70445, TPS70448

TPS70451, TPS70458

TPS70402

SLVS307F –SEPTEMBER 2000–REVISED APRIL 2010

www.ti.com

Comparing P

D(total)

with P

D(max)

reveals that the power dissipation in this example does not exceed the calculated

limit. When it does, one of two corrective actions should be made: raising the power-dissipation limit by

increasing the airflow or the heat-sink area, or lowering the internal power dissipation of the regulator by reducing

the input voltage or the load current. In either case, the above calculations should be repeated with the new

system parameters. This parameter is measured with the recommended copper heat sink pattern on a 4-layer

PWB, 2 oz. copper traces on 4-in × 4-in ground layer. Simultaneous and continuous operation of both regulator

outputs at full load may exceed the power dissipation rating of the PWP package.

Mounting Information

The primary requirement is to complete the thermal contact between the thermal pad and the PWB metal. The

thermal pad is a solderable surface and is fully intended to be soldered at the time the component is mounted.

Although voiding in the thermal-pad solder-connection is not desirable, up to 50% voiding is acceptable. The data

included in Figure 34 and Figure 36 are for soldered connections with voiding between 20% and 50%. The

thermal analysis shows no significant difference resulting from the variation in voiding percentage.

Figure 37 shows the solder-mask land pattern for the PWP package. The minimum recommended heat-sink area

is also illustrated. This is simply a copper plane under the body extent of the package, including metal routed

under terminals 1, 12, 13, and 24.

Figure 37. PWP Package Land Pattern