OPA333 datasheet(25/58 Pages) TI2

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circumstances may arise where an applied voltage exceeds the operating voltage range of a given pin. Should

this condition occur, there is a risk that some internal ESD protection circuits may be biased on, and conduct

current. Any such current flow occurs through steering-diode paths and rarely involves the absorption device.

Figure 8-4 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 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.

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 may be supplied by the input source through 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 any uncertainty about the ability of the supply to absorb this current, external zener diodes must be

added to the supply pins, as shown in Figure 8-4. 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.

8.3.7 MUX-Friendly Inputs

The OPAx189 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

anti-parallel diodes that protect input transistors from large VGS voltages that may 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.

OPAx189 solves these problems with a switched-input technique that prevents large input bias currents when

large differential voltages are applied. This solves many issues seen in switched or multiplexed applications,

where large disruptions to RC filtering networks are caused by fast switching between large potentials. OPAx189

offers outstanding settling performance due to these design innovations and built-in slew rate boost and wide

bandwidth. The OPAx189 can also be used as a comparator. Differential and common-mode Absolute Maximum

Ratings still apply relative to the power supplies.

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OPA189, OPA2189, OPA4189

SBOS830I – SEPTEMBER 2017 – REVISED OCTOBER 2021

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OPA333 Datasheet(PDF) 25 Page - Texas Instruments