OPAX187 datasheet(21/54 Pages) TI2

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Op Amp

Core

(See

Note 1)

OUT

+IN

ESD Current-

Steering Diodes

V+

(See Note 3)

TVS

(See Note 2)

Edge-Triggered ESD

Absorption Circuit

V±

TVS

(See Note 2)

OPA187, OPA2187, OPA4187

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SBOS807E – DECEMBER 2016 – REVISED MAY 2020

Product Folder Links: OPA187 OPA2187 OPA4187

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Another common question involves what happens to the amplifier if an input signal is applied to the input while

power supply +VS or –VS is at 0 V. Again, this question depends on the supply characteristic while at 0 V, or at a

level less than the input signal amplitude. If the supplies are 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 will 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 transient voltage

suppressor (TVS) diodes to the supply pins, as shown in Figure 39. Select the TVS voltage so that the diode

does not turn on during normal operation. However, make sure that the TVS voltage is low enough so that the

TVS diode conducts if the supply pin exceeds the safe operating supply voltage level.

NOTE 1: VIN = +VS + 500 mV.

NOTE 2: TVS: +VS(max) > VTVSBR (min) > +VS.

NOTE 3: Suggested value is approximately 1 kΩ.

Figure 39. Equivalent Internal ESD Circuitry Relative to a Typical Circuit Application

The OPAx187 input pins are protected from excessive differential voltage with back-to-back diodes, as shown in

Figure 39. 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. 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 can be used to limit the signal input current. This input series resistor degrades

the low-noise performance of the OPAx187. Figure 39 shows an example configuration that implements a

current-limiting feedback resistor.

7.4 Device Functional Modes

The OPAx187 have a single functional mode and are operational when the power-supply voltage is greater than

4.5 V (±2.25 V). The maximum power supply voltage for the OPAx187 is 36 V (±18 V).

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