BQ24004 Datasheet, PDF (18/22 Pages) Texas Instruments – TWO-CELL Li-ION CHARGE MANAGEMENT IC FOR PDAs AND INTERNET APPLIANCES

bq24004
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SLUS476B – DECEMBER 2000 – REVISED MAY 2002
THERMAL INFORMATION
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THERMALLY ENHANCED TSSOP-20
The thermally enhanced PWP package is based on the
20-pin TSSOP, but includes a thermal pad (see
Figure 20) 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 20. 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 22(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 Figure 22(b) and 22(c).) The
line drawn at 0.3 cm² in Figures 21 and 22 indicates
performance at the minimum recommended heat-sink
size.
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