Datasheet

DIE

Side View(a)

EndView(b)

DIE

Thermal

Pad

BottomView(c)

TPS70445, TPS70448

TPS70451, TPS70458

TPS70402

SLVS307F –SEPTEMBER 2000–REVISED APRIL 2010

www.ti.com

THERMAL INFORMATION

Thermally-Enhanced TSSOP-24 (PWP— PowerPAD™)

The thermally-enhanced PWP package is based on the 24-pin TSSOP, but includes a thermal pad [see

Figure 33(c)] to provide an effective thermal contact between the IC and the printed wiring board (PWB).

Traditionally, surface mount and power have been mutually exclusive terms. A variety of scaled-down

TO220-type packages have leads formed as gull wings to make them applicable for surface-mount applications.

These packages, however, suffer from several shortcomings: they do not address the very low profile

requirements (<2 mm) of many of today’s advanced systems, and they do not offer a pin-count high enough to

accommodate increasing integration. On the other hand, traditional low-power surface-mount packages require

power-dissipation derating that severely limits the usable range of many high-performance analog circuits.

The PWP package (thermally-enhanced TSSOP) combines fine-pitch surface-mount technology with thermal

performance comparable to much larger power packages.

The PWP package is designed to optimize the heat transfer to the PWB. Because of the very small size and

limited mass of a TSSOP package, thermal enhancement is achieved by improving the thermal conduction paths

that remove heat from the component. The thermal pad is formed using a lead-frame design (patent pending)

and manufacturing technique to provide the user with direct connection to the heat-generating IC. When this pad

is soldered or otherwise coupled to an external heat dissipator, high power dissipation in the ultrathin, fine-pitch,

surface-mount package can be reliably achieved.

Figure 33. Views of Thermally-Enhanced PWP Package

Because the conduction path has been enhanced, power-dissipation capability is determined by the thermal

considerations in the PWB design. For example, simply adding a localized copper plane (heat-sink surface),

which is coupled to the thermal pad, enables the PWP package to dissipate 2.5 W in free air (reference

Figure 35(a), 8 cm

of copper heat sink and natural convection). Increasing the heat-sink size increases the

power dissipation range for the component. The power dissipation limit can be further improved by adding airflow

to a PWB/IC assembly (see Figure 34 and Figure 35). The line drawn at 0.3 cm

in Figure 34 and Figure 35

indicates performance at the minimum recommended heat-sink size, illustrated in Figure 36.