The OPA810 does not require a heat sink or airflow in most applications. Maximum allowed junction temperature sets the maximum allowed internal power dissipation. Do not allow the maximum junction temperature to exceed 150°C.

Operating junction temperature (T_J) is given by T_A + P_D × θ_JA. The total internal power dissipation (P_D) is the sum of quiescent power (P_DQ) and additional power dissipated in the output stage (P_DL) to deliver load power. Quiescent power is the specified no-load supply current times the total supply voltage across the part. P_DL depends on the required output signal and load, but for a grounded resistive load, is at a maximum when the output is fixed at a voltage equal to half of either supply voltage (for equal split-supplies). Under this condition, P_DL = V_S² / (4 × R_L) where R_L includes feedback network loading.

The power in the output stage and not into the load that determines internal power dissipation.

As a worst-case example, compute the maximum T_J using a DCK (SC70 package) configured as a unity gain buffer, operating on ±12-V supplies at an ambient temperature of 25°C and driving a grounded 500-Ω load.

P_D = 24 V × 4.7 mA + 12² / (4 × 500 Ω) = 184.8 mW

Maximum T_J = 25°C + (0.185 W × 190.8°C/W) = 60°C, which is much less than the maximum allowed junction temperature of 150°C.