10

20

30

40

50

60

70

10

100

Capacitive Load (pF)

RISO = 0

Ÿ

RISO = 25

Ÿ

RISO = 50

Ÿ

C004

18

OPA187, OPA2187, OPA4187

SBOS807 – DECEMBER 2016

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Product Folder Links: OPA187 OPA2187 OPA4187

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Copyright © 2016, Texas Instruments Incorporated

Figure 39. Small-Signal Overshoot Versus Capacitive Load

7.3.7 Electrical Overstress

Designers often ask questions about the capability of an operational amplifier to withstand electrical overstress.

These questions tend to focus on the device inputs, but may involve the supply voltage pins or even the output

pin. Each of these different pin functions have electrical stress limits determined by the voltage breakdown

characteristics of the particular semiconductor fabrication process and specific circuits connected to the pin.

Additionally, internal electrostatic discharge (ESD) protection is built into these circuits to protect them from

accidental ESD events both before and during product assembly.

Having a good understanding of this basic ESD circuitry and its relevance to an electrical overstress event is

helpful. See Figure 40 for an illustration of the ESD circuits contained in the OPAx187 (indicated by the dashed

line area). The ESD protection circuitry involves several current-steering diodes connected from the input and

output pins and routed back to the internal power-supply lines, where the diodes meet at an absorption device

internal to the operational amplifier. This protection circuitry is intended to remain inactive during normal circuit

operation.

An ESD event produces a short-duration, high-voltage pulse that is transformed into a short-duration, high-

current pulse while discharging through a semiconductor device. The ESD protection circuits are designed to

provide a current path around the operational amplifier core to prevent damage. The energy absorbed by the

protection circuitry is then dissipated as heat.

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 may activate. The

absorption device has a trigger, or threshold voltage, that is above the normal operating voltage of the OPAx187

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 (as shown in Figure 40), 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. 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.

applications limit the input current to 10 mA.

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.