The maximum power allowed to dissipate in a device is defined as:

where

• P_D is the power dissipation in a device
• T_J(max) is the maximum junction temperature
• T_A is the ambient temperature
• R_θJA is the thermal resistance of a particular package

For example, for the LM7171 in a SOIC-8 package, the maximum power dissipation at 25°C ambient temperature is 730mW.

Thermal resistance, R _θJA, depends on parameters such as die size, package size and package material. The smaller the die size and package, the higher R_θJA becomes. The 8-pin DIP package has a lower thermal resistance (108°C/W) than that of 8-pin SOIC (172°C/W). Therefore, for higher dissipation capability, use an 8-pin DIP package.

The total power dissipated in a device can be calculated as:

where

• P_Q is the quiescent power dissipated in a device with no load connected at the output. P_L is the power dissipated in the device with a load connected at the output; P_L is not the power dissipated by the load.

  Furthermore,

• P_Q is the supply current × total supply voltage with no load
• P_L is the output current × (voltage difference between supply voltage and output voltage of the same side of supply voltage)

For example, the total power dissipated by the LM7171 with V_S = ±15V and output voltage of 10V into 1kΩ is