OPA2180
OPA4180
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SBOS584B –NOVEMBER 2011–REVISED DECEMBER 2011
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.
These ESD protection diodes also provide in-circuit, input overdrive protection, as long as the current is limited to
10 mA as stated in the Absolute Maximum Ratings. Figure 29 shows how a series input resistor may be added to
the driven input to limit the input current. The added resistor contributes thermal noise at the amplifier input and
its value should be kept to a minimum in noise-sensitive applications.
V+
IOVERLOAD
10 mA max
VOUT
Device
VIN
5 kW
Figure 29. Input Current Protection
An ESD event produces a short duration, high-voltage pulse that is transformed into a short duration,
high-current pulse as it discharges through a semiconductor device. The ESD protection circuits are designed to
provide a current path around the operational amplifier core to prevent it from being damaged. The energy
absorbed by the protection circuitry is then dissipated as heat.
When the operational amplifier connects into a circuit, the ESD protection components are intended to remain
inactive and 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 of the internal ESD protection circuits may be biased on, and conduct current. Any such current flow
occurs through ESD cells and rarely involves the absorption device.
If there is an uncertainty about the ability of the supply to absorb this current, external zener diodes may be
added to the supply pins. The zener voltage must be selected such that the diode does not turn on during normal
operation.
However, its zener voltage should be low enough so that the zener diode conducts if the supply pin begins to
rise above the safe operating supply voltage level.
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