OPA1612-Q1 Datasheet, PDF (16/31 Pages) Texas Instruments – SoundPlus High-Performance, Bipolar-Input Audio Operational Amplifier

OPA1612-Q1
SLOS931A – NOVEMBER 2015 – REVISED NOVEMBER 2015
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Feature Description (continued)
If the supply is not capable of sinking the current, V_IN may begin sourcing current to the operational amplifier, and
then take over as the source of positive supply voltage. The danger in this case is that the voltage can rise to
levels that exceed the operational amplifier absolute maximum ratings. In extreme but rare cases, the absorption
device triggers on while +V_S and –V_S are applied. If this event happens, a direct current path is established
between the +V_S and –V_S supplies. The power dissipation of the absorption device is quickly exceeded, and the
extreme internal heating destroys the operational amplifier.
Another common question involves what happens to the amplifier if an input signal is applied to the input while
the power supplies +V_S or –V_S are at 0 V. Again, the result depends on the supply characteristic while at 0 V, or
at a level below the input signal amplitude. If the supplies appear as high impedance, then the operational
amplifier supply current may be supplied by the input source via the current steering diodes. This state is not a
normal bias condition; the amplifier most likely does not operate normally. If the supplies are low impedance,
then the current through the steering diodes can become quite high. The current level depends on the ability of
the input source to deliver current, and any resistance in the input path.
If there is an uncertainty about the ability of the supply to absorb this current, external zener diodes may be
added to the supply pins; see Figure 35. The zener voltage must be selected such that the diode does not turn
on during normal operation. However, the zener diode voltage must be low enough so that the zener diode
conducts if the supply pin begins to rise above the safe operating supply voltage level.
8.3.3 Operating Voltage
The OPA1612-Q1 op amp operates from ±2.25-V to ±18-V supplies while maintaining excellent performance.
The OPA1612-Q1 device can operate with as little as +4.5 V between the supplies and with up to +36 V between
the supplies. However, some applications do not require equal positive and negative output voltage swing. With
the OPA1612-Q1 device, power-supply voltages do not need to be equal. For example, the positive supply could
be set to +25 V with the negative supply at –5 V.
In all cases, the common-mode voltage must be maintained within the specified range. In addition, key
parameters are assured over the specified temperature range of T_A = –40°C to +85°C. Parameters that vary with
operating voltage or temperature are shown in the Typical Characteristics section.
8.3.4 Input Protection
The input terminals of the OPA1612-Q1 device is protected from excessive differential voltage with back-to-back
diodes, as Figure 36 shows. In most circuit applications, the input protection circuitry has no consequence.
However, in low-gain or G = +1 circuits, fast ramping input signals can forward bias these diodes because the
output of the amplifier cannot respond rapidly enough to the input ramp. This effect is illustrated in Figure 17 of
the Typical Characteristics section. If the input signal is fast enough to create this forward bias condition, the
input signal current must be limited to 10 mA or less. If the input signal current is not inherently limited, an input
series resistor (R_I) or a feedback resistor (R_F) can be used to limit the signal input current. This input series
resistor degrades the low-noise performance of the OPA1612-Q1 device and is examined in the Noise
Performance section. Figure 36 shows an example configuration when both current-limiting input and feedback
resistors are used.
R_F
–
Input
R_I
+
Device
Output
Figure 36. Pulsed Operation
16
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