ADA4051-1/ADA4051-2

Data Sheet

Rev. C | Page 18 of 22

The design architecture of the ADA4051-1/ADA4051-2

specifically targets precision signal conditioning applications

requiring accurate and stable performance from dc to 10 Hz

bandwidth. In summary, the main features of the ADA4051-1/

ADA4051-2 chopper amplifiers are

•

Considerable suppression of the offset-related ripple

•

No effect on the desired input signal as long as its

frequency is much lower than the chopping frequency

shown in Figure 60

•

Achievement of low offset similar to a conventional

chopper amplifier

•

No introduction of excess noise

The ADA4051-1/ADA4051-2 chopper amplifiers provide a rail-

to-rail input range with a 1.8 V to 5.5 V supply voltage range and

20 µA supply current consumption over the −40°C to +125°C

extended industrial temperature range. The gain bandwidth is

125 kHz as a unity-gain stable amplifier up to 100 pF load

capacitance.

INPUT VOLTAGE RANGE

The ADA4051-1/ADA4051-2 have internal ESD protection

diodes. These diodes are connected between the inputs and each

supply rail to protect the input MOSFETs from an electrical

discharge event and are reversed-biased during normal operation.

This protection scheme allows voltages as high as approximately

0.3 V beyond the supplies (±VSY ± 0.3 V) to be applied at the

input of either terminal without causing permanent damage.

If either input exceeds one of the supply rails by more than 0.3 V,

these ESD diodes become forward-biased and large amounts of

current begin to flow through them. Without current limiting, this

excessive current would cause permanent damage to the device.

If the inputs are expected to be subject to overvoltage conditions,

install a resistor in series with each input to limit the input current

to 10 mA maximum.

The ADA4051-1/ADA4051-2 also have internal circuitry that

protects the input stage from high differential voltages. This

circuitry is composed of internal 1.33 kΩ resistors in series with

each input and back-to-back diode-connected N-MOSFET (with a

typical VT of 0.7 V for a VCM of 0 V) after these series resistors. With

normal negative feedback operating conditions, the ADA4051-1/

ADA4051-2 amplifiers correct their output to ensure that the two

inputs are at the same voltage. However, if the device is configured

as a comparator or there are unusual operating conditions, the

input voltages can be forced to different potentials, which may

cause excessive current to flow through the internal diode-

connected N-MOSFETs.

Although the ADA4051-1/ADA4051-2 are rail-to-rail input

amplifiers, take care to ensure that the potential difference

between the inputs does not exceed ±VSY to avert permanent

damage to the device.

OUTPUT PHASE REVERSAL

Although output phase reversal can occur with other amplifiers

when the input common-mode voltage range is exceeded, the

ADA4051-1/ADA4051-2 amplifiers are designed to prevent

any output phase reversal, provided both inputs are maintained

approximately within 0.3 V above and below the supply voltages

(±VSY ± 0.3 V).

With other amplifiers, the outputs may jump in the opposite

direction to the supply rail when a common-mode voltage

moves outside the common-mode range. This usually occurs

when one of the internal stages of the amplifier no longer has

sufficient bias voltage across it and subsequently turns off.

However, with the ADA4051-1/ADA4051-2 amplifiers, if one

or both inputs exceed the input voltage range but remain within

the ±VSY ± 0.3 V range, an internal loop opens and the output

remains in saturation mode, without phase reversal, until the

input voltage is brought back to within the input voltage range

limits as shown in Figure 55 and Figure 58.