7.3 Feature Description

7.3.1 Input and ESD Protection

The OPAx328 incorporates internal electrostatic discharge (ESD) protection circuits on all pins. In the case of

input and output pins, this protection primarily consists of current-steering diodes connected between the input

and power-supply pins. These ESD protection diodes also provide in-circuit input overdrive protection, provided

that the current is limited to 10 mA. Many input signals are inherently current-limited to less than 10 mA;

to the driven input to limit the input current. The added resistor contributes thermal noise at the amplifier input;

therefore, keep this value to a minimum in noise-sensitive applications.

V+

Amp

10 mA Max

+

–

Figure 7-1. Input Current Protection

7.3.2 Rail-to-Rail Input

The OPAx328 features true rail-to-rail input operation, with supply voltages as low as ±1.1 V (2.2 V). The

design of the OPAx328 amplifiers include an internal charge-pump that powers the amplifier input stage with an

the single differential input pair to operate and remain very linear over a very-wide input common-mode

range. A unique zero-crossover input topology eliminates the input offset transition region typical of many

rail-to-rail, complementary-input-stage, operational amplifiers. This topology allows the OPAx328 to provide

superior common-mode performance (CMRR > 120 dB, typical) over the entire common-mode input range,

which extends 100 mV beyond both power-supply rails. When driving analog-to-digital converters (ADCs), the

7.3.3 Phase Reversal

The OPAx328 op amps are designed to be immune to phase reversal when the input pins exceed the supply

voltages, and thus provide further in-system stability and predictability. Figure 7-2 shows the input voltage

exceeding the supply voltage without any phase reversal.

Time (100 µs/div)

Figure 7-2. No Phase Reversal

7.4 Device Functional Modes

The OPAx328 operational amplifier is operational when power-supply voltages between 2.2 V to 5.5 V are

applied. Devices with an S suffix have shutdown capability.

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OPA2328

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