AD8479 Precision Difference Amplifier: Pinout and Basic Connections

Pinout

Pin Function Descriptions

Symbol

Footprint

3D Model

The AD8479 is a difference amplifier with a very high input common-mode voltage range. The AD8479 is a precision device that allows the user to accurately measure differential signals in the presence of high common-mode voltages up to ±600 V.

This article provides you with a basic overview of the AD8479 Precision Difference Amplifier, including its pin descriptions, features and specifications, etc., to help you quickly understand what AD8479 is.

● ±600 V common-mode voltage range

● Rail-to-rail output

● Fixed gain of 1

● Wide power supply range of ±2.5 V to ±18 V

● 550 μA typical power supply current

● Excellent ac specifications

   ◆ 90 dB minimum CMRR

   ◆ 310 kHz bandwidth

● High accuracy dc performance

   ◆ 5 ppm maximum gain nonlinearity

   ◆ 10 μV/°C maximum offset voltage drift

   ◆ 5 ppm/°C maximum gain drift 

The AD8479 can replace costly isolation amplifiers in applications that do not require galvanic isolation. The device operates over a ±600 V common-mode voltage range and has inputs that are protected from common-mode or differential mode transients up to ±600 V. The AD8479 has low offset voltage, low offset voltage drift, low gain drift, low common-mode rejection drift, and excellent common-mode rejection ratio (CMRR) over a wide frequency range. The AD8479 is available in a space-saving 8-lead SOIC package and is operational over the −40°C to +125°C temperature range.

The AD8479 is a unity-gain, differential-to-single-ended amplifier that can reject extremely high common-mode signals up to 600 V with ±15 V supplies. The AD8479 consists of an operational amplifier (op amp) and a resistor network (As shown in the figure below). 

Functional Block Diagram

To achieve the high common-mode voltage range, an internal resistor divider—connected to Pin 3 and Pin 5—attenuates the noninverting signal by a factor of 60. The internal resistors at Pin 1 and Pin 2, as well as the feedback resistor, restore the gain to provide a differential gain of unity.

The complete transfer function is: V_OUT = V (+IN) − V (−IN)

Laser wafer-trimming provides resistor matching so that common-mode signals are rejected and differential input signals are amplified.

To reduce output voltage drift, the op amp uses super beta transistors in its input stage. The input offset current and its associated temperature coefficient contribute no appreciable output voltage offset or drift, which has the added benefit of reducing voltage noise because the corner where 1/f noise becomes dominant is below 5 Hz. To reduce the dependence of gain accuracy on the op amp, the open-loop voltage gain of the op amp exceeds 20 million V/V, and the PSRR exceeds 90 dB.

The figure below shows the basic connections for operating the AD8479 with a dual supply. A supply voltage from ±2.5 V to ±18 V is applied across Pin 7 and Pin 4. Both supplies should be decoupled close to the pins using 0.1 μF capacitors. Electrolytic capacitors of 10 μF, also located close to the supply pins, may be required if low frequency noise is present on the power supply. Although multiple amplifiers can be decoupled by a single set of 10 μF capacitors, each AD8479 should have its own set of 0.1 μF capacitors so that the decoupling point can be located directly at the IC power pins.

Basic Connections

The differential input signal, which typically results from a load current flowing through a small shunt resistor, is applied to Pin 2 and Pin 3 with the polarity shown in previous figure to obtain a positive gain. The common-mode voltage on the differential input signal can range from −600 V to +600 V, and the maximum differential voltage is ±14.7 V. When configured as shown in previous figure, the device operates as a simple gain-of-1, differentialto-single-ended amplifier where the output voltage is the shunt resistance times the shunt current. The output is measured with respect to Pin 1 and Pin 5.

Pin 1 and Pin 5 (REF(−) and (REF(+)) should be grounded for a gain of unity and connected to the same low impedance ground plane. Failure to do this results in degraded common-mode rejection. Pin 8 is a no connect pin and should be left open. 

● High voltage current sensing

● Battery cell voltage monitors

● Power supply current monitors

● Motor controls

● Isolation

Analog Devices is an international market leader in the design, production, and commercialization of a large range of high-performance integrated circuits (ICs) for analog, mixed-signal, and digital signals (DSP) processing of almost all electronic systems. Since we started in 1965, the focus has been on the engineering challenge in electronic equipment related to signal to process. Our signal processing solutions, utilized by over 100,000 customers worldwide, play a key role in the conversion, conditioning, and processing of real-world events such as temperature, pressure, sonority, illumination, speed, and movement to electric signals for a wide range of electronic devices.

Download datasheets and manufacturer documentation for Analog Devices Inc. AD8479ARZ.