Texas Instruments has designed a new true low-profile 20-pin, power package. With a thermal resistance, ROJC, of just 3.5° C/W, this surface mount package has comparable thermal performance to many conventional power packages - it is able to dissipate over 2 watts. The new patent-pending package, designated the PWP, is designed to maximize heat transfer away from the die through a thermal pad on its underside. A special downset leadframe (see cutaway view) puts the die in direct contact with the pad, conducting head directly away to the printed circuit board. This has been done without exceeding the maximum 1.15 mm height of TSSOP. The eight corner pins are used for additional head conduction, leaving 12 active pins. Its higher pin count and ultra-low profile bring analog power functions to surface mount systems.
The first device to be offered in this package is the TPS7133QPWP 3.3-V low dropout (LDO) voltage regulator. The TPS7133PWP features very low dropout voltage, stable 350 ľA (max) quiescent current, a micropower shutdown mode, and more (see related article on page 2). Figure 1 illustrates the thermal properties of the PWP package mounted against 1 oz/ft2 copper heatsinking board etch. Airflow, etch area, and layout can be optimized for maximum power dissipation. In the new PWP package, the TPS7133 can deliver its rated 500-mA load current - even when stepping down from 5 V - in compact surface mount systems.
Vol 11, Spring, 1995