ADA4622-2 datasheet(23/28 Pages) AD

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Data Sheet

ADA4622-2

Rev. 0 | Page 23 of 28

The ADA4622-2 is designed for 12 nV/√Hz wideband input

voltage noise and maintains low noise performance at low

frequencies (see Figure 75). This noise performance, along with

the low input current as well as low current noise, means that

the ADA4622-2 contributes 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)

ADA4622-2 VOLTAGE AND CURRENT NOISE

RS NOISE

TOTAL NOISE

Figure 75. Total Noise vs. Source Resistance

Input Overvoltage Protection

The ADA4622-2 has internal protective circuitry that allows

voltages as high as 0.3 V beyond the supplies to be applied at the

input of either terminal without causing damage. Use a current

limiting resistor in series with the input of the ADA4622-2 if

the input voltage exceeds 0.3 V beyond the supplies. If the

overvoltage condition persists for more than a few seconds,

the amplifier may be damaged.

For higher input voltages, determine the resistor value by

≤

−

where:

VIN is the input voltage.

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

RS is the series resistor.

With a very low 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

amplifier 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.

EMI Rejection

Figure 76 shows the electromagnetic interference rejection ratio

(EMIRR) vs. frequency for the ADA4622-2.

100

10M

100M

FREQUENCY (Hz)

COMPETITOR 1

COMPETITOR 2

ADA4622-2

Figure 76. EMI Rejection Ratio (EMIRR) vs. Frequency

OUTPUT CHARACTERISTICS

The ADA4622-2 unique bipolar rail-to-rail output stage swings

within 10 mV of the supplies with no external resistive load.

The ADA4622-2 approximate output saturation resistance 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 roughly 120 mV.

If the ADA4622-2 output is driven hard against the output

saturation voltage, it recovers within 1.2 µs of the input, returning

to the amplifiers linear operating region (see Figure 48 and

Figure 51).

Capacitive Load Drive Capability

Direct capacitive loads interact with the effective output

impedance of the ADA4622-2 to form an additional pole in the

amplifier feedback loop, which causes excessive peaking on the

pulse response or loss of stability. The worst case condition is

when the device is used single 5 V supply and in a unity-gain

configuration. Figure 77 shows the pulse response of the

ADA4622-2 driving 500 pF directly.

CH1 50.0mV BW

M2.00µs

A CH1

108mV

Figure 77. Pulse Response with 500 pF Load Capacitance

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