OPA1692 Datasheet, PDF (11/23 Pages) Texas Instruments – Low-Power, Low-Noise and Low-Distortion Audio Operational Amplifiers

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OPA1692, OPA1694
SBOS566 – JUNE 2017
Feature Description (continued)
When an ESD voltage develops across two or more amplifier device pins, current flows through one or more
steering diodes. Depending on the path that the current takes, the absorption device can activate. The absorption
device has a trigger, or threshold voltage, that is above the normal operating voltage of the OPA169x but below
the device breakdown voltage level. When this threshold is exceeded, the absorption device quickly activates
and clamps the voltage across the supply rails to a safe level.
When the operational amplifier connects into a circuit (refer to Figure 9), the ESD protection components are
intended to remain inactive and do not become involved in the application-circuit operation. However,
circumstances may arise where an applied voltage exceeds the operating voltage range of a given pin. If this
condition occurs, there is a risk that some internal ESD protection circuits can turn on and conduct current. Any
such current flow occurs through steering-diode paths and rarely involves the absorption device.
Figure 9 shows a specific example where the input voltage (V_IN) exceeds the positive supply voltage (V+) by 500
mV or more. Much of what happens in the circuit depends on the supply characteristics. If V+ can sink the
current, one of the upper input steering diodes conducts and directs current to V+. Excessively high current
levels can flow with increasingly higher V_IN. As a result, the data sheet specifications recommend that
applications limit the input current to 10 mA.
If the supply is not capable of sinking the current, V_IN can 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.
Another common question involves what happens to the amplifier if an input signal is applied to the input when
the power supplies (V+ or V–) are at 0 V. Again, this question depends on the supply characteristic when at 0 V,
or at a level below the input signal amplitude. If the supplies appear as high impedance, then the input source
supplies the operational amplifier current through the current-steering diodes. This state is not a normal bias
condition; most likely, the amplifier 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 any uncertainty about the ability of the supply to absorb this current, add external Zener diodes to the
supply pins; see Figure 9. Select the Zener voltage so that the diode does not turn on during normal operation.
However, the Zener 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.
7.4 Device Functional Modes
7.4.1 Operating Voltage
The OPA169x series op amps operate from ±1.75 V to ±18 V supplies while maintaining excellent performance.
The OPA169x series can operate with as little as 3.5V 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
OPA169x series, 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
significantly with operating voltage or temperature are shown in the Typical Characteristics.
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