1.6MHz Bandwidth, Low Noise Precision Op‐amps

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Rev. A

Input ESD Diode Protection

The TP2331 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, as long as the current is limited to

10 mA as stated in the Absolute Maximum Ratings table. Many input signals are inherently current-limited to less than

10 mA; therefore, a limiting resistor is not required. Figure 2 shows how a series input resistor (RS) may be added to

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

value should be kept to the minimum in noise-sensitive applications.

IN+

IN-

V+

V-

500Ω

500Ω

INPUT ESD DIODE CURRENT LIMITING- UNITY GAIN

 

Figure2. Input ESD Diode

EMI Susceptibility and Input Filtering

Operational amplifiers vary in susceptibility to electromagnetic interference (EMI). If conducted EMI enters the device,

the dc offset observed at the amplifier output may shift from the nominal value while EMI is present. This shift is a result

of signal rectification associated with the internal semiconductor junctions. While all operational amplifier pin functions

can be affected by EMI, the input pins are likely to be the most susceptible. The TP2331 operational amplifier family

incorporates an internal input low-pass filter that reduces the amplifier response to EMI. Both common-mode and

differential mode filtering are provided by the input filter. The filter is designed for a cutoff frequency of approximately

400 MHz (–3 dB), with a roll-off of 20 dB per decade.

Figure 3. TP2331 EMIRR IN+ vs Frequency

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Frequency (MHz)