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

amp. Equation 6 shows the calculation of TJ for the OPAx591 assuming an 85V power supply is used and an

operating temperature of 25°C.

TJ= 85V ×490μA ×165.4°CW+25°C

(6)

TJ=31.89°C

(7)

The low power consumption of the OPAx591 causes minimal self-heating even in a small SOT23-5 package as

given by Equation 7. 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 8.

PDL= V+ 24×RL

(8)

For example, assume the OPAx591 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 9. 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. The calculation for a 5kΩ load is depicted visually in Figure 7-9.

∆TJ= 41.7mW+90.3mW ×165.4°CW

(9)

For high-voltage amplifiers such as the OPAx591, the junction temperature can easily be tens of degrees

higher than the ambient temperature in a quiescent (unloaded) condition. As shown by Equation 5, the junction

temperature depends on the thermal properties of the package, as expressed by the junction-to-ambient thermal

resistance (RϴJA). If the device then begins to drive a heavy load, the junction temperature can rise and trip

the thermal-shutdown circuit. Figure 7-9 shows the maximum output voltage versus ambient temperature to

avoid exceeding the Absolute Maximum Ratings in both loaded and unloaded conditions for the SOT23-5

package version of the OPA591. The curve assumes a typical quiescent current and does not account for any

temperature variation of quiescent current.

Ambient Temperature ( C)

85

95

105

115

125

135

145

0

10

20

30

40

50

60

70

80

90

100

Unloaded

Loaded (2k )

Loaded (10k )

Figure 7-9. OPA591 (SOT23-5) Thermal Safe

Operating Area

Temperature ( C)

65

75

85

95

105

115

125

135

145

0

10

20

30

40

50

60

70

80

90

100

Unloaded

Loaded (10k )

Loaded (2k )

Figure 7-10. OPA2591 (VSSOP-8) Thermal Safe

Operating Area

OPA591, OPA2591

SBOSA47 – FEBRUARY 2026

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