16-PIN SURFACE

MOUNT

L*

H*

LM7372

SNOS926E – MAY 1999 – REVISED MARCH 2013

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The required signal swing can be reduced by using a step-up transformer to drive the line. For example a 1:2

ratio will reduce the peak swing requirement by half, and this would allow the supply to be reduced by a

corresponding amount. This is not recommended for the LM7372 in this particular application for two reasons.

Although the quiescent power contribution to the overall dissipation is reduced by about 150mW, the internal

power dissipation to drive the load remains the same, since the load for each amplifier is now 25

Ω instead of

100

Ω. Furthermore, this is a transceiver application where downstream signals are simultaneously appearing at

the transformer secondary. The down stream signals appear differentially across the back termination resistors

and are now stepped down by the transformer turns ratio with a consequent loss in receiver sensitivity compared

to using a 1:1 transformer. Any trade-off to reduce the supply voltage by an increase in turns ratio should bear

these factors in mind, as well as the increased signal current levels required with lower impedance loads.

At an elevated ambient temperature of 85°C and with an average power dissipation of 464mW, a package

thermal resistance between 60°C/W and 80°C/W will be needed to keep the maximum junction temperature in

the range 110°C to 120°C. The SO PowerPAD package would be the package of choice here with ample board

copper area to aid in heat dissipation (see Table 2).

For most standard surface mount packages, 8-Pin SOIC, 14-Pin SOIC, 16-Pin SOIC etc, the only means of heat

removal from the die is through the bond wires to external copper connecting to the leads. Usually it will be

difficult to reduce the thermal resistance of these packages below 100°C/W by these methods and several

manufacturers, including Texas Instruments, offer package modifications to enhance the thermal characteristics.

Figure 26. Copper Heatsink Patterns

The LM7372 is available in the 16-Pin SOIC package. Since only 8 pins are needed for the two operational

amplifiers, the remaining pins are used for heat sink purposes. Each of the end pins, 1,8,9 & 16 are internally

bonded to the lead frame and form an effective means of transferring heat to external copper. This external

copper can be either electrically isolated or be part of the topside ground plane in a single supply application.

Figure 26 shows a copper pattern which can be used to dissipate internal heat from the LM7372. Table 1 gives

some values of

Table 1. 16-Pin SOIC Thermal Resistance with Area of Cu

L (in)

H (in)

1

0.5

83

2

1

70

3

1.5

67

14

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