OPA197 Datasheet, PDF (22/41 Pages) Texas Instruments – Operational Amplifiers

OPA197, OPA2197, OPA4197
SBOS737 – JANUARY 2016
www.ti.com
7.3.3 Phase Reversal Protection
The OPAx197 family has internal phase-reversal protection. Many op amps exhibit a phase reversal when the
input is driven beyond its linear common-mode range. This condition is most often encountered in noninverting
circuits when the input is driven beyond the specified common-mode voltage range, causing the output to
reverse into the opposite rail. The OPAx197 is a rail-to-rail input op amp; therefore, the common-mode range can
extend up to the rails. Input signals beyond the rails do not cause phase reversal; instead, the output limits into
the appropriate rail. This performance is shown in Figure 45.
Output
Input
Time (200 Ps/div)
Figure 45. No Phase Reversal
7.3.4 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 OPAx197 is 150°C.
Exceeding this temperature causes damage to the device. The OPAx197 has a thermal protection feature that
prevents 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 140°C. Figure 46 shows an application example for
the OPA197 that has significant self heating (159°C) 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 187°C.
The actual device, however, turns off the output drive to maintain a safe junction temperature. Figure 46 depicts
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 140°C, the thermal
protection forces the output to a high-impedance state and the output is pulled to ground through resistor RL.
+30 V
TA = 65°C
PD = 0.81W
JA = 116°C/W
TJ = 116°C/W × 0.81W + 65°C
TJ = 159°C (expected)
VOUT 3 V
0V
OPAx197
+ V_IN
± ^3V
IOUT = 30 mA
+
RL
3V
100 Ÿ _±
Normal
Operation
Output
High-Z
150°C
140ºC
Figure 46. Thermal Protection
7.3.5 Capacitive Load and Stability
The OPAx197 features a patented output stage capable of driving large capacitive loads, and in a unity-gain
configuration, directly drives up to 1 nF of pure capacitive load. Increasing the gain enhances the ability of the
amplifier to drive greater capacitive loads; see Figure 47 and Figure 48. 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.
22
Submit Documentation Feedback
Copyright © 2016, Texas Instruments Incorporated
Product Folder Links: OPA197 OPA2197 OPA4197