ADA4622-2ACPZ-R7 datasheet(25/34 Pages) AD

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Data Sheet

ADA4622-1/ADA4622-2

Rev. B | Page 25 of 34

The ADA4622-1/ADA4622-2 are designed for 12 nV/√Hz

wideband input voltage noise density and maintain low noise

performance at low frequencies (see Figure 83). This noise

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

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

contribute negligible noise for applications with a source resistance

greater than 10 kΩ and at signal bandwidths greater than 1 kHz.

10k

100k

FREQUENCY (Hz)

ADA4622-1/ADA4622-2 VOLTAGE AND CURRENT NOISE

RS NOISE

TOTAL NOISE

Figure 83. Total Noise vs. Source Resistance

Input Overvoltage Protection

The ADA4622-1/ADA4622-2 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 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 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 84 shows the EMI rejection ratio (EMIRR) vs. the

frequency for the ADA4622-1/ADA4622-2.

100

FREQUENCY (Hz)

COMPETITOR 1

COMPETITOR 2

ADA4622-1/ADA4622-2

Figure 84. EMIRR vs. Frequency

OUTPUT CHARACTERISTICS

The ADA4622-1/ADA4622-2 unique bipolar rail-to-rail output

stage swings within 10 mV of the supplies with no external

resistive load.

The ADA4622-1/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 ADA4622-1/ADA4622-2 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 55 and Figure 58).

Capacitive Load Drive Capability

Direct capacitive loads interact with the effective output impedance

of the ADA4622-1/ADA4622-2 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 85 shows the pulse response of the

ADA4622-1/ADA4622-2 driving 500 pF directly.

CH1 50.0mV BW

M2.00µs

A CH1

108mV

Figure 85. Pulse Response with 500 pF Load Capacitance

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