GENERAL DESCRIPTION

The ADA4522-1/ADA4522-2/ADA4522-4 are single/dual/quad channel, zero drift op amps with low noise and power, ground sensing inputs, and rail-to-rail output, optimized for total accuracy over time, temperature, and voltage conditions. The wide operating voltage and temperature ranges, as well as the high open-loop gain and very low dc and ac errors make the devices well suited for amplifying very small input signals and for accurately reproducing larger signals in a wide variety of applications.

The ADA4522-1/ADA4522-2/ADA4522-4 performance is specified at 5.0 V, 30 V, and 55 V power supply voltages. These devices operate over the range of 4.5 V to 55 V, and are excellent for applications using single-ended supplies of 5 V, 10 V, 12 V, and 30 V, or for applications using higher single supplies and dual supplies of ±2.5 V, ±5 V, and ±15 V. The ADA4522-1/ADA4522-2/ADA4522-4 use on-chip filtering to achieve high immunity to electromagnetic interference (EMI).

The ADA4522-1/ADA4522-2/ADA4522-4 are fully specified over the extended industrial temperature range of −40°C to +125°C and are available in 8-lead MSOP, 8-lead SOIC, 14-lead SOIC, and 14-lead TSSOP packages.

 

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.

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 .

 

Single-Supply Instrumentation Amplifier

The extremely low offset voltage and drift, high open-loop gain, high common-mode rejection, and high power supply rejection of the ADA4522-1/ADA4522-2/ADA4522-4 make them excellent op amp choices as discrete, singlesupply instrumentation amplifiers.