10.4 Power Dissipation

Power dissipation depends on power supply, signal, and load conditions. It is dominated by the power dissipation of the output transistors of the OPA. For DC signals, power dissipation is equal to the product of output current, I_OUT and the output voltage across the conducting output transistor (V_S – V_OUT).

It is very important to note that the temperature protection does not shut the device down in overtemperature conditions, unless the EF_OT pin is connected to the output enable pin OD; see the Driver Output Disable section.

The power that can be safely dissipated in the package is related to the ambient temperature and the heat sink design and conditions. The VQFN package with an exposed thermal pad is specifically designed to provide excellent power dissipation, but board layout greatly influences the heat dissipation.

To appropriately determine the required heat sink area, calculate required power dissipation; also consider the relationship between power dissipation and thermal resistance to minimize overheat conditions and allow for reliable long-term operation.

The heat-sinking efficiency can be tested using the EF_OT output signal. This output goes low at nominally 140°C junction temperature (assume 6% tolerance). With full power dissipation (for example, maximum current into a 0-Ω load), the ambient temperature can be slowly raised until the OT flag goes low. This flag would indicate the minimum heat sinking for the usable operation condition.

The recommended landing pattern for the VQFN package is shown at the end of this data sheet.