ADA4522-4ARZ-R7 datasheet(28/48 Pages) AD

28 / 48 page

Data Sheet

ADA4522-1/ADA4522-

2/ADA4522-4

analog.com

Rev I 28 of 48

THEORY OF OPERATION

The ADA4522-1/ADA4522-2/ADA4522-4 are single, dual, and quad, ultralow noise, high voltage, zero drift, rail-to-rail

output operational 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 voltages 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 architecture 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 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 information).

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

Gm1

Gm2

Gm3

EMI

FILTER

AND

CLAMP

THERMAL

SHUTDOWN

OFFSET

AND RIPPLE

CORRECTION

LOOP

+IN x

–IN x

CHOPIN

CHOPOUT

OUT

4.8MHz CLOCKS

800kHz CLOCKS

CLOCK

GENERATOR

NOTES

1. THE INPUTS ARE +IN x/–IN x ON THE ADA4522-2 AND ADA4522-4,

AND +IN/–IN ON THE ADA4522-1.

2. THE OUTPUT IS OUT ON THE ADA4522-1 AND OUT x ON THE

ADA4522-2 AND ADA4522-4.

ADA4522-4ARZ-R7 Datasheet(PDF) 28 Page - Analog Devices

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