7.3.2 Power Dissipation

The INA1620 is capable of high output current with power-supply voltages up to ±18 V. Internal power dissipation increases when operating at high supply voltages. The power dissipated in the op amp (P_OPA) is calculated using Equation 1:

In order to calculate the worst-case power dissipation in the op amp, the ac and dc cases must be considered separately.

In the case of constant output current (dc) to a resistive load, the maximum power dissipation in the op amp occurs when the output voltage is half the positive supply voltage. This calculation assumes that the op amp is sourcing current from the positive supply to a grounded load. If the op amp sinks current from a grounded load, modify Equation 2 to include the negative supply voltage instead of the positive.

The maximum power dissipation in the op amp for a sinusoidal output current (ac) to a resistive load occurs when the peak output voltage is 2/π times the supply voltage, given symmetrical supply voltages:

The dominant pathway for the INA1620 to dissipate heat is through the package thermal pad and pins to the PCB. Copper leadframe construction used in the INA1620 improves heat dissipation compared to conventional materials. PCB layout greatly affects thermal performance. Connect the INA1620 package thermal pad to a copper pour at the most negative supply potential. This copper pour can be connected to a larger copper plane within the PCB using vias to improve power dissipation. Figure 45 shows an analogous thermal circuit that can be used for approximating the junction temperature of the INA1620. The power dissipated in the INA1620 is represented by current source P_D; the ambient temperature is represented by voltage source 25ºC; and the junction-to-board and board-to-ambient thermal resistances are represented by resistors R_θJB and R_θBA, respectively. The board-to-ambient thermal resistance is unique to every application. The sum of R_θJB and R_θBA is the junction-to-ambient thermal resistance of the system. The value for junction-to-ambient thermal resistance reported in the Thermal Information table is determined using the JEDEC standard test PCB. The voltages in the analogous thermal circuit at the points T_J and T_PCB represent the INA1620 junction and PCB temperatures, respectively.