ADA4051-2ARMZ-R7 datasheet(16/20 Pages) AD

16 / 20 page

ADA4051-2

Rev. 0 | Page 16 of 20

The voltage noise density is essentially flat from dc to the

chopping frequency, whose level is just the thermal noise floor

dominated by the Gm1, without receiving any addition due

to the ACFB. Although the ACFB suppresses the ripple related

to the chopping, there is a remaining voltage ripple. To further

suppress the remaining ripple down to a desired level, it is

recommended to have a post filter at the output of the amplifier.

The remaining voltage ripple is composed of two ingredients.

The first ripple’s ingredient is due to the residual ripple associated

with the initial offset of the Gm1. It is proportional to the mag-

nitude of the initial offset and creates a spectrum at the chopping

frequency (fCHOP). When the amplifier is configured as a unity

gain buffer, this ripple has a typical value of 4.9 μV rms and a

maximum of 34.7 μV rms. The second ripple’s ingredient is due

to the intermodulation between the high frequency input signal

and the chopping frequency. It depends on the input frequency

(fIN) and creates a spectrum at frequencies equal to the dif-

ference between the chopping frequency and the input

frequency (fCHOP − fIN) and at their summation (fCHOP + fIN).

The magnitude of the ripple for different input frequencies

is shown in Figure 57.

100

200

300

400

500

0123456789

INPUT FREQUENCY (kHz)

Figure 57. ADA4051-2 Modulated Output Ripple vs. Input Frequency

The design architecture of the 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 ADA4051-2 chopper

amplifier are

•

Considerable suppression of the offset-related ripple

•

No affect on the desired input signal as long as its

frequency is much lower than the chopping frequency

shown in Figure 57

•

Achievement of low offset similar to a conventional

chopper amplifier

•

No introduction of excess noise

The ADA4051-2 chopper amplifier provides rail-to-rail input

range with 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 ADA4051-2 has internal ESD protection diodes. These

diodes are connected between the inputs and each supply rail

to protect the input MOSFETs against an electrical discharge

event and are normally reversed-biased. 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 either supply rail 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 causes permanent damage to the device.

If the inputs are expected to be subject to overvoltage condi-

tions, install a resistor in series with each input to limit the

input current to 10 mA maximum.

The ADA4051-2 also has 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-MOSFETs (with a typical VT of

0.7 V for VCM of 0 V) after these series resistors. Under normal

negative feedback operating conditions, the ADA4051-2 amplifier

corrects its output to ensure the two inputs are at the same voltage.

However, if the device is configured as a comparator or is under

some unusual operating condition, the input voltages may be

forced to different potentials, which may cause excessive

current to flow through the internal diode-connected N-

MOSFETs.

Although the ADA4051-2 is a rail-to-rail input amplifier, take

care to ensure that the potential difference between the inputs

does not exceed ±VSY to avert permanent damage to the device.

ADA4051-2ARMZ-R7 Datasheet(PDF) 16 Page - Analog Devices

ADA4051-2ARMZ-R7 Datasheet(HTML) 16 Page - Analog Devices

Html Pages

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20

Datasheet Download

Link URL