ADA4075-2ACPZ-R7 datasheet(17/25 Pages) AD

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ADA4075-2

Data Sheet

Rev. C | Page 16 of 24

APPLICATIONS INFORMATION

INPUT PROTECTION

To prevent base-emitter junction breakdown from occurring in

the input stage of the ADA4075-2 when a very large differential

voltage is applied, the inputs are clamped by the internal diodes

to ±1.2 V. To preserve the ultralow voltage noise feature of the

ADA4075-2, the commonly used internal current-limiting

resistors in series with the inputs are not used.

In small signal applications, current limiting is not required;

however, in applications where the differential voltage of the

ADA4075-2 exceeds ±1.2 V, large currents may flow through

these diodes. Employ external current-limiting resistors as

shown in Figure 63 to reduce the input currents to less than

±10 mA. Note that depending on the value of these resistors,

the total voltage noise will most likely be degraded. For example,

a 1 kΩ resistor at room temperature has a thermal noise of

4 nV/√Hz, whereas the ADA4075-2 has an ultralow voltage

noise of only 2.8 nV/√Hz typical.

ADA4075-2

Figure 63. Input Protection

TOTAL HARMONIC DISTORTION

The total harmonic distortion + noise (THD + N) of the

ADA4075-2 is 0.0002% typical with a load resistance of 2 kΩ.

Figure 64 shows the performance of the ADA4075-2 driving a

2 kΩ load with supply voltages of ±4 V and ±15 V. Notice that

there is more distortion for the supply voltage of ±4 V than for a

supply voltage of ±15 V. Therefore, it is important to operate the

ADA4075-2 at a supply voltage greater than ±5 V for optimum

distortion. The THD + noise graphs for supply voltages of ±5 V

and ±18 V are available in Figure 56 and Figure 61.

0.0001

0.001

0.01

0.1

100

10k

100k

FREQUENCY (Hz)

VSY = ±4V

RL = 2kΩ

VIN = 1.5V rms

VSY = ±15V

RL = 2kΩ

VIN = 3V rms

Figure 64. THD + Noise vs. Frequency

PHASE REVERSAL

An undesired phenomenon, phase reversal (also known as phase

inversion) occurs in many op amps when one or both of the

inputs are driven beyond the specified input common-mode

voltage (VICM) range, in effect reversing the polarity of the output.

In some cases, phase reversal can induce lockups and cause

equipment damage as well as self destruction.

The ADA4075-2 incorporates phase reversal prevention circuitry

that clamps the output to 2 V typical from the supply rails when

one or both inputs exceed the VICM range. Figure 65 shows the

input/output waveforms of the ADA4075-2 configured as a unity-

gain buffer for a supply voltage of ±15 V.

VIN

VOUT

TIME (40µs/DIV)

VSY = ±15V

Figure 65. No Phase Reversal

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