OPA186DBVT datasheet(22/48 Pages) TI

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Figure 7-4 shows a specific example where the input voltage (VIN) 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 +VS. Excessively high

current levels can flow with increasingly higher VIN. 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, VIN 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 while

the power supplies V+ or V– are at 0 V. Again, this question 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 can be supplied by the input source through the current-steering diodes. This state is

not a normal biasing condition for the amplifier and can result in specification degradation or abnormal operation.

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 also Figure 7-4. The Zener voltage must be selected such 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.

7.3.6 MUX-Friendly Inputs

The OPAx186 features a proprietary input stage design that allows an input differential voltage to be applied

while maintaining high input impedance. Typically, high-voltage CMOS or bipolar-junction input amplifiers feature

antiparallel diodes that protect input transistors from large VGS voltages that can exceed the semiconductor

process maximum and permanently damage the device. Large VGS voltages can be forced when applying a

large input step, switching between channels, or attempting to use the amplifier as a comparator.

The OPAx186 solves these problems with a switched-input technique that prevents large input bias currents

when large differential voltages are applied. This input architecture addresses many issues seen in switched or

multiplexed applications, where large disruptions to RC filtering networks are caused by fast switching between

large potentials. The OPAx186 offers outstanding settling performance as a result of these design innovations

and built-in slew-rate boost and wide bandwidth. The OPAx186 can also be used as a comparator. Differential

and common-mode input ranges still apply.

7.4 Device Functional Modes

The OPAx186 has a single functional mode, and is operational when the power-supply voltage is greater than

4.5 V (±2.25 V). The maximum power supply voltage for the OPAx186 is 24 V (±12 V).

OPA186, OPA2186, OPA4186

SBOS968B – JUNE 2022 – REVISED DECEMBER 2022

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OPA186DBVT датащи(PDF) 22 Page - Texas Instruments