6.3.2 Thermal Protection

The OPAx591 has a thermal protection feature that prevents damage from self heating. When the junction

temperature (TJ) reaches approximately 170ºC, the op amp output stage disables. This thermal protection works

by monitoring the temperature of the output stage and turning off the op amp output drive. Thermal protection

forces the output to a high-impedance state. The OPAx591 is designed with approximately 20°C of thermal

hysteresis and returns to normal operation when the output stage temperature becomes less than approximately

150°C.

This thermal protection is not designed to prevent this device from exceeding absolute maximum ratings, but

rather from excessive thermal overload.

6.3.3 Advanced Slew Boost

Slew rate is the maximum rate of change of output voltage change with respect to time and is typically specified

in units of volts per microsecond, V/µs. Op amps can enter a slew condition when a large, rapid moving signal

is applied at the input. While slewing, the op amp enters an open loop condition and significant slew induced

distortion can be seen on the output signal.

Equation 1 shows that the slew rate, SR, of an op amp is typically determined by the saturation current of the

input stage, ITAIL, and the compensation capacitor, CC.

SR=ITAILCC

(1)

Slew rate typically scales with the quiescent current, IQ, of the op amp. There are several ways that designers

have overcome slew rate limitation. For example, lowering CC, commonly known as decompensation, improves

slew rate at the expense of stability. Decompensated op amps require a minimum gain and are not stable

at unity gain. More commonly, modern op amps are equipped with slew boost technology that increases ISAT

to improve slew rate. Slew boost circuits can vary in implementation, but typically, expect about a four-fold

improvement over comparable unboosted op amps.

The OPAx591 uses a proprietary design to achieve an unprecedented slew rate to IQ ratio. The novel slew boost

technology in OPAx591 provides a nearly 100 × slew rate improvement over comparable unboosted op amps.

The op amp is unity gain stable and can be used configured as a buffer if desired.

Table 6-1 shows a comparison of slew rates and quiescent currents of different op amps.

Table 6-1. Op Amp Slew Rates and Quiescent

Current

PART NUMBER

SLEW RATE

QUIESCENT

CURRENT

OPAx591

100V/µs

420µA

OPAx188

0.8V/µs

425µA

OPAx202

0.35V/µs

580µA

OPAx192

20V/µs

1mA

OPA454

13V/µs

3.2mA

OPA591, OPA2591

SBOSA47 – FEBRUARY 2026

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