TPS70451 Datasheet, PDF (20/32 Pages) Texas Instruments – DUAL-OUTPUT LOW-DROPOUT VOLTAGE REGULATORS WITH INTEGRATED SVS FOR SPLIT VOLTAGE SYSTEMS

TPS70445, TPS70448, TPS70451, TPS70458, TPS70402
DUAL-OUTPUT LOW-DROPOUT VOLTAGE REGULATORS
WITH INTEGRATED SVS FOR SPLIT VOLTAGE SYSTEMS
SLVS307B – SEPTEMBER 2000 – REVISED APRIL 2003
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 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.
DIE
Side View (a)
DIE
End View (b)
Thermal
Pad
Bottom View (c)
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 cm² 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 Figures 34 and 35). The line drawn at 0.3 cm² in Figures 34 and 35 indicates
performance at the minimum recommended heat-sink size, illustrated in Figure 36.
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