8.4.1.1 Thermal Considerations

Through normal operation, the OPA593 self-heats. Self-heating is a natural increase in the die junction

temperature that occurs in every amplifier. The maximum allowed junction temperature sets the maximum

allowed internal power dissipation (PD) as described in the following paragraph. Design efforts should be made

to prevent TJ from exceedeing the maximum temperature listed in the Absolute Maximum Ratings table.

Operating junction temperature (TJ) is determined by the ambient temperature (TA), the internal PD under the

operating conditions, and the junction-to-ambient thermal resistance (RθJA). This relationship is given by TA +

(PD × RθJA). PD is the sum of quiescent power (PDQ) and additional power dissipated in the output stage (PDL)

when delivering power to the load. PDQ is the specified no-load supply current times the total supply voltage

across the part. PDL depends on the required output signal and load, but for a grounded resistive load the PDL

is at a maximum when the output is fixed at a voltage equal to 1/2 of either supply voltage (for balanced bipolar

supplies, V+ and V−). Under this condition PDL = (V+)2 / (4 × RL), where RL includes feedback network loading.

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

As a worst-case example, compute the maximum TJ using the OPA593 in the circuit of Figure 8-1 operating at a

maximum specified temperature of 125°C and driving a grounded 600-Ω load.

PD = PDQ + PDL

(4)

PD= 50 V×4 mA + 22.52 V 

4 × 600 Ω   11.47 kΩ

(5)

TJmax = 125°C + 0.422 W × 40.8°C/W = 142.2°C

(6)

To enhance semiconductor long-term operating life, minimize TJ. Take proper measures to provide maximum

heat removal through both heat conduction and radiation to help keep TJ to the lowest possible level. These

proper measures include maximizing the PCB copper area to which the package thermal pad is soldered. The

copper area serves as the traditional heat sink. The top layer copper is often easiest to route and is most often

exposed to open air. PCB internal planes and the exposed bottom plane can also be used as heat sinks, but the

connections are made with vias having higher thermal resistance. The OPA593EVM uses a board design that

provides a highly effective thermal layout. The board design encompasses a large top-side copper area, and has

heat conduction paths to other planes on the board. Additionally, other higher power-dissipating components are

kept physically distant from the OPA593 to better accommodate heat removal by radiation.

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OPA593

SBOS659C – JANUARY 2022 – REVISED DECEMBER 2022

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