7.4.1.1 Thermal Considerations

Through normal operation, the op amps can self-heat. Self-heating is a natural increase in the die junction

temperature that occurs in every amplifier. This self-heating is a result of several factors, including quiescent

power consumption, package thermal resistance, PCB layout, and device operating conditions.

Operate the OPAx596 within the rated junction temperature, TJ, range to avoid thermal shutdown. Use the

Equation 2 to determine the estimated TJ

TJ=PD × θJA+TA

(2)

In a quiescent state, PD is given by the product of the power supply and the quiescent current of the op

amp. Equation 3 shows the calculation of TJ for the OPAx596 assuming an 85V power supply is used and an

operating temperature of 25°C.

TJ= 85V ×490μA ×165.4°CW+25°C

(3)

TJ=31.89°C

(4)

The low power consumption of the OPAx596 causes minimal self-heating even in a small SOT23-5 package as

given by Equation 4. In a loaded condition, PD is equal to addition of the quiescent power, PDQ and the power

dissipated by the output stage, PDL. The worst-case condition is given when the output voltage is equal to ½

of either supply rail (assuming symmetrical supplies, V+ and V-). In a worst-case condition, PDL is given by

Equation 5.

PDL= V+ 24×RL

(5)

For example, assume the OPAx596 is powered with bipolar ±42.5V power supplies and drives a 5kΩ load, RL, to

ground. The maximum increase in TJ is expected to be about 22°C as given by Equation 6. In this example, to

keep the op amp within the Absolute Maximum Ratings, operate in TA well under 128°C to account for different

factors.

∆TJ= 41.7mW+90.3mW ×165.4°CW

(6)

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OPA596

SBOSA42 – JUNE 2024

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