OPA2991IDSGR datasheet(24/78 Pages) TI

24 / 78 page

7.3.3 Thermal Protection

The internal power dissipation of any amplifier causes its internal (junction) temperature to rise. This

phenomenon is called self heating. The absolute maximum junction temperature of the OPAx991 is 150°C.

Exceeding this temperature causes damage to the device. The OPAx991 has a thermal protection feature that

reduces damage from self heating. The protection works by monitoring the temperature of the device and turning

off the op amp output drive for temperatures above 170°C. Figure 7-4 shows an application example for the

OPA991 that has significant self heating because of its power dissipation (0.81 W). Thermal calculations indicate

that for an ambient temperature of 65°C, the device junction temperature must reach 177°C. The actual device,

however, turns off the output drive to recover towards a safe junction temperature. Figure 7-4 shows how the

circuit behaves during thermal protection. During normal operation, the device acts as a buffer so the output is

3 V. When self heating causes the device junction temperature to increase above the internal limit, the thermal

protection forces the output to a high-impedance state and the output is pulled to ground through resistor RL.

If the condition that caused excessive power dissipation is not removed, the amplifier will oscillate between a

shutdown and enabled state until the output fault is corrected.

170ºC

3 V

0 V

30 V

100

VIN

3 V

–

OUT = 30 mA

OPA991

TA = 65°C

PD = 0.81W

JA = 138.7°C/W

TJ = 138.7°C/W × 0.81W + 65°C

TJ = 177.3°C (expected)

–

Figure 7-4. Thermal Protection

If the device continues to operate at high junction temperatures with high output power over a long period of

time, regardless if the device is or is not entering thermal shutdown, the thermal dissipation of the device can

slowly degrade performance of the device and eventually cause catastrophic destruction. Designers should be

careful to limit output power of the device at high temperatures, or control ambient and junction temperatures

under high output power conditions.

7.3.4 Capacitive Load and Stability

The OPAx991 features a resistive output stage capable of driving moderate capacitive loads, and by leveraging

an isolation resistor, the device can easily be configured to drive large capacitive loads. Increasing the gain

enhances the ability of the amplifier to drive greater capacitive loads; see Figure 7-5 and Figure 7-6. The

particular op amp circuit configuration, layout, gain, and output loading are some of the factors to consider when

establishing whether an amplifier will be stable in operation.

OPA991, OPA2991, OPA4991

SBOS969F – OCTOBER 2019 – REVISED JANUARY 2022

www.ti.com

Submit Document Feedback

Product Folder Links: OPA991 OPA2991 OPA4991

OPA2991IDSGR Datasheet(PDF) 24 Page - Texas Instruments

OPA2991IDSGR Datasheet(HTML) 24 Page - Texas Instruments

Html Pages

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78

Datasheet Download

Link URL