ADA4522-4ARZ-R7 datasheet(22/33 Pages) AD

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Data Sheet

ADA4522-1/ADA4522-2/ADA4522-4

THEORY OF OPERATION

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Rev. G | 22 of 33

The ADA4522-1/ADA4522-2/ADA4522-4 are single, dual, and

quad, ultralow noise, high voltage, zero drift, rail-to-rail output op-

erational amplifiers. They feature a chopping technique that offers

an ultralow input offset voltage of 5 µV and an input offset voltage

drift of 22 nV/°C maximum for the ADA4522-1 and ADA4522-2 and

25 nV/°C maximum for the ADA4522-4. Offset voltage errors due to

common-mode voltage swings and power supply variations are also

corrected by the chopping technique, resulting in a superb typical

CMRR figure of 160 dB and a PSRR figure of 160 dB at a 30 V

supply voltage.

The ADA4522-1/ADA4522-2/ADA4522-4 have wide operating vol-

tages from ±2.25 V (or 4.5 V) to ±27.5 V (or 55 V). The devices are

single supply amplifiers, where their input voltage range includes

the lower supply rail. They also offer low voltage noise density

of 5.8 nV/√Hz (at f = 1 kHz, AV = 100) and reduced 1/f noise

component. These features are ideal for the amplification of low

level signals in high precision applications. A few examples of such

applications are weigh scales, high precision current sensing, high

voltage buffers, and signal conditioning for temperature sensors,

among others.

Figure 71 shows the ADA4522-1/ADA4522-2/ADA4522-4 architec-

ture block diagram. The architecture consists of an input EMI

filter and clamp circuitry, three gain stages (Gm1, Gm2, and Gm3),

input and output chopping networks (CHOPIN and CHOPOUT), a

clock generator, offset and ripple correction loop circuitry, frequency

compensation capacitors (C1, C2, and C3), and thermal shutdown

circuitry.

An EMI filter and clamp circuit is implemented at the input front end

to protect the internal circuitry against electrostatic discharge (ESD)

stresses and high voltage transients. The ability of the amplifier to

reject EMI is explained in detail in the EMI Rejection Ratio section.

CHOPIN and CHOPOUT are controlled by a clock generator and

operate at 4.8 MHz. The input baseband signal is initially modulated

by CHOPIN. Next, CHOPOUT demodulates the input signal and

modulates the millivolt level input offset voltage and 1/f noise of the

input transconductance amplifier, Gm1, to the chopping frequency

at 4.8 MHz. The chopping networks remove the low frequency

errors, but, in return, the networks introduce chopping artifacts at

the chopping frequency. Therefore, a offset and ripple correction

loop, operating at 800 kHz, is used. This frequency is the switching

frequency of the amplifier. This circuitry reduces chopping artifacts,

allowing the ADA4522-1/ADA4522-2/ADA4522-4 to have a high

chopping frequency with minimal artifacts.

The thermal shutdown circuit shuts down the circuit when the die

is overheated (see the Thermal Shutdown section for more informa-

tion).

Figure 71. ADA4522-1/ADA4522-2/ADA4522-4 Architecture Block Diagram

ON-CHIP INPUT EMI FILTER AND CLAMP

CIRCUIT

Figure 72 shows the input EMI filter and clamp circuit. TheA-

DA4522-1/ADA4522-2/ADA4522-4 have internal ESD protection

diodes (D1, D2, D3, and D4) that are connected between the inputs

and each supply rail. These diodes protect the input transistors in

the event of electrostatic discharge and are reverse biased during

normal operation. This protection scheme allows voltages as high

as approximately 300 mV beyond the rails to be applied at the input

of either terminal without causing permanent damage. See Table 5

in the Absolute Maximum Ratings section for more information.

The EMI filter is composed of two 200 Ω input series resistors (RS1

and RS2), two common-mode capacitors (CCM1 and CCM2), and

a differential capacitor (CDM). These RC networks set the −3 dB

low-pass cutoff frequencies at 50 MHz for common-mode signals,

and at 33 MHz for differential signals. After the EMI filter, back

to back diodes (D5 and D6) are added to protect internal circuit

devices from high voltage input transients. Each diode has about

1 V of forward turn on voltage. See the Large Signal Transient

Response section for more information on the effect of high voltage

input transient on the ADA4522-1/ADA4522-2/ADA4522-4.

As specified in the Absolute Maximum Ratings section (see Table

5), the maximum input differential voltage is limited to ±5 V. If more

than ±5 V is applied, a continuous current larger than ±10 mA

flows through one of the back to back diodes. This current compro-

mises long-term reliability and can cause permanent damage to the

device.

Figure 72. Input EMI Filter and Clamp Circuit

THERMAL SHUTDOWN

The ADA4522-1/ADA4522-2/ADA4522-4 have internal thermal

shutdown circuitry for each channel of the amplifier. The thermal

shutdown circuitry prevents internal devices from being damaged

by an overheat condition in the die. Overheating can occur due to a

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