Datasheet

LM7372
www.ti.com SNOS926E –MAY 1999–REVISED MARCH 2013
From Table 1 it is apparent that two areas of 1oz copper at each end of the package, each 2 in
2
in area (for a
total of 2600mm
2
) will be sufficient to hold the maximum junction temperature under 120°C with an 85°C ambient
temperature.
An even better package for removing internally generated heat is a package with an exposed die attach paddle.
Improved removal of internal heat can be achieved by directly connecting bond wires to the lead frame inside the
package. Since this lead frame supports the die attach paddle, heat is transferred directly from the substrate to
the outside copper by these bond wires. The LM7372 is also available in the 8-Pin SO PowerPAD package. For
this package the entire lower surface of the paddle is not covered with plastic, which would otherwise act as a
thermal barrier to heat transfer. Heat is transferred directly from the die through the paddle rather than through
the small diameter bonding wires. Values of θ
JA
in °C/W for the SO PowerPAD package with various areas and
weights of copper are tabulated below.
Table 2. Thermal Resistance of SO PowerPAD Package
Copper Area 0.5 in
2
1.0 in
2
2.0 in
2
(each side) (each side) (each side)
0.5 oz Top 115 105 102
1.0 oz Layer 91 79 72
2.0 oz Only 74 60 52
0.5 oz Bottom 102 88 81
1.0 oz Layer 92 75 65
2.0 oz Only 85 66 54
0.5 oz Top And Bottom 83 70 63
1.0 oz 71 57 47
2.0 oz 63 48 37
Table 2 clearly demonstrates the superior thermal qualities of the exposed pad package. For example, using the
topside copper only in the same way as shown for the SOIC package (Figure 26), the SO PowerPAD requires
half the area of 1 oz copper (2 in
2
, total or 1300mm
2
), for a comparable thermal resistance of 72°C/Watt. This
gives considerably more flexibility in the pcb layout aside from using less copper.
The shape of the heat sink shown in Figure 26 is necessary to allow external components to be connected to the
package pins. If thermal vias are used beneath the SO PowerPAD to the bottom side ground plane, then a
square pattern heat sink can be used and there is no restriction on component placement on the top side of the
board. Even better thermal characteristics are obtained with bottom layer heat sinking. A 2 inch square of 0.5oz
copper gives the same thermal resistance (81°C/W) as a competitive thermally enhanced 8-Pin SOIC package
which needs two layers of 2 oz copper, each 4 in
2
(for a total of 5000 mm
2
). With heavier copper, thermal
resistances as low as 54°C/W are possible with bottom side heat sinking only, substantially improving the long
term reliability since the maximum junction temperature is held to less than 110°C, even with an ambient
temperature of 85°C. If both top and bottom copper planes are used, the thermal resistance can be brought to
under 40°C/W.
HIGH FREQUENCY/LARGE SIGNAL SWING CONSIDERATIONS
The LM7372 employs a unique input stage in order to support large slew rate and high output current capability
with large output swings, with a relatively low quiescent current. This input architecture boosts the device supply
current when the application demands it. The result is a supply current which increases at high enough
frequencies when the output swing is large enough with added power dissipation as a consequence.
Figure 27 shows the amount of increase in supply current as a function of frequency for various sinusoidal output
swing amplitudes:
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