OPA2320-Q1_15 Datasheet, PDF(13/31 Page) Texas Instruments – Precision, 20-MHz, 0.9-pA, Low-Noise, RRIO,CMOS Operational Amplifier

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OPA2320-Q1_15 Datasheet, PDF (13/31 Pages) Texas Instruments – Precision, 20-MHz, 0.9-pA, Low-Noise, RRIO,CMOS Operational Amplifier

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Feature Description (continued)

OPA2320-Q1

SLOS884 â SEPTEMBER 2014

V(V+)

I(OVERLOAD)

10 mA, Max

OPA320-Q1

R(S)

Figure 29. Input Current Protection

7.3.2 Feedback Capacitor Improves Response

For optimum settling time and stability with high-impedance feedback networks, adding a feedback capacitor

across the feedback resistor, R(FB), as shown in Figure 30 may be necessary. This capacitor compensates for the

zero created by the feedback network impedance and the OPA2320-Q1 device input capacitance (and any

parasitic layout capacitance). The effect becomes more significant with higher impedance networks.

C(F)

R(IN)

R(F)

V(V+)

R(IN) Ã C(IN) = R(F) Ã C(F)

C(IN)

OPA320-Q1

C(IN)

C(L)

Note:

Where C(IN) is equal to the OPA2320-Q1 input capacitance (approximately 9 pF) plus any parasitic layout

capacitance.

Figure 30. Feedback Capacitor Improves Dynamic Performance

It is suggested that a variable capacitor be used for the feedback capacitor because input capacitance may vary

between op amps and layout capacitance is difficult to determine. For the circuit shown in Figure 30, the value of

the variable feedback capacitor should be chosen so that the input resistance times the input capacitance of the

OPA2320-Q1 device (9 pF typical) plus the estimated parasitic layout capacitance equals the feedback capacitor

times the feedback resistor:

R(IN) Ã C(IN) = R(FB) Ã C(FB)

Where:

â¢ C(IN) is equal to the OPA2320-Q1 input capacitance (sum of differential and common-mode) plus the layout

capacitance.

(1)

The capacitor value can be adjusted until optimum performance is obtained.

7.3.3 EMI Susceptibility And Input Filtering

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

operational amplifier, 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 OPA2320-Q1 operational amplifier family incorporates an internal input low-pass filter that reduces the

amplifiers response to EMI. Both common-mode and differential mode filtering are provided by the input filter.

The filter is designed for a cut-off frequency of approximately 580 MHz (â3 dB), with a roll-off of 20 dB per

decade.

Product Folder Links: OPA2320-Q1

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