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ADA4622-1/ADA4622-2/ADA4622-4

Data Sheet

Rev. E | Page 28 of 38

The ADA4622-1/ADA4622-2/ADA4622-4 are designed for

12 nV/√Hz wideband input voltage noise density and maintain

low noise performance at low frequencies (see Figure 84). This

noise performance, along with the low input current as well as

low current noise, means that the ADA4622-1/ADA4622-2/

ADA4622-4 contribute negligible noise for applications with a

source resistance greater than 10 kΩ and at signal bandwidths

greater than 1 kHz.

10k

100k

100

10k

100k

FREQUENCY (Hz)

ADA4622-1/ADA4622-2/ADA4622-4 VOLTAGE

AND CURRENT NOISE

RS NOISE

TOTAL NOISE

Figure 84. Total Noise vs. Source Resistance and Frequency

Input Overvoltage Protection

The ADA4622-1/ADA4622-2/ADA4622-4 have internal

protective circuitry that allows voltages as high as 0.3 V beyond

the supplies applied at the input of either terminal without

causing damage. Use a current-limiting resistor in series with the

input of the ADA4622-1/ADA4622-2/ADA4622-4 if the input

voltage exceeds 0.3 V beyond the supply rails of the amplifiers. If

the overvoltage condition persists for more than a few seconds,

damage to the amplifiers can result.

For higher input voltages, determine the resistor value by

≤

−

where:

VIN is the input voltage.

VSY is the voltage of either the V+ pin or the V− pin.

RS is the series resistor.

With a very low input bias current of ±1.5 nA maximum up to

125°C, higher resistor values can be used in series with the inputs

without introducing large offset errors. A 1 kΩ series resistor

allows the ADA4622-1/ADA4622-2/ADA4622-4 to withstand

10 V of continuous overvoltage and increases the noise by a

negligible amount. A 5 kΩ resistor protects the inputs from

voltages as high as 25 V beyond the supplies and adds less than

10 µV to the offset voltage of the amplifiers.

EMI Rejection Ratio

Figure 85 shows the EMI rejection ratio (EMIRR) vs. the

frequency for the ADA4622-1/ADA4622-2/ADA4622-4.

100

10M

100M

FREQUENCY (Hz)

COMPETITOR 1

COMPETITOR 2

ADA4622-1/ADA4622-2/ADA4622-4

Figure 85. EMIRR vs. Frequency

OUTPUT CHARACTERISTICS

The ADA4622-1/ADA4622-2/ADA4622-4 unique bipolar rail-

to-rail output stage swings within 10 mV of the supplies with no

external resistive load.

The approximate output saturation resistance of the ADA4622-1/

ADA4622-2/ADA4622-4 is 24 Ω, sourcing or sinking. Use the

output impedance to estimate the output saturation voltage when

driving heavier loads. As an example, when driving 5 mA, the

saturation voltage from either rail is approximately 120 mV.

If the ADA4622-1/ADA4622-2/ADA4622-4 output drives hard

against the output saturation voltage, it recovers within 1.2 µs of the

input, returning to the linear operating region of the amplifier

(see Figure 56 and Figure 59).

Capacitive Load Drive Capability

Direct capacitive loads interact with the effective output impedance

of the ADA4622-1/ADA4622-2/ADA4622-4 to form an

additional pole in the feedback loop of the amplifiers, which

causes excessive peaking on the pulse response or loss of

stability. The worst case condition is when the devices use a single

5 V supply in a unity-gain configuration. Figure 86 shows the

pulse response of the ADA4622-1/ADA4622-2/ADA4622-4

when driving 500 pF directly.

CH1 50.0mV BW

M2.00µs

A CH1

108mV

Figure 86. Pulse Response with 500 pF Load Capacitance

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