LM7372

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SNOS926E – MAY 1999 – REVISED MARCH 2013

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

weights of copper are tabulated below.

Table 2. Thermal Resistance of SO PowerPAD Package

Copper

Area

(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

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

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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