High Common-Mode Voltage, Programmable Gain Difference Amplifier

The AD628 is a precision difference amplifier that combines excellent dc performance with high common-mode rejection over a wide range of frequencies. When used to scale high voltages, it allows simple conversion of standard control voltages or currents for use with single-supply ADCs. A wideband feedback loop minimizes distortion effects due to capacitor charging of Σ-Δ ADCs.

A reference pin (VREF) provides a dc offset for converting bipolar to single-sided signals. The AD628 converts +5 V, +10 V, ±5 V, ±10 V, and 4 to 20 mA input signals to a single-ended output within the input range of single-supply ADCs.

The AD628 has an input common mode and differential mode operating range of ±120 V. The high common mode, input impedance makes the device well suited for high voltage measurements across a shunt resistor. The inverting input of the buffer amplifier is available for making a remote Kelvin connection.

A precision 10 kΩ resistor connected to an external pin is provided for either a low-pass filter or to attenuate large differential input signals. A single capacitor implements a low-pass filter. The AD628 operates from single and dual supplies and is available in an 8-lead SOICN or an 8-lead MSOP. It operates over the standard industrial temperature range of −40°C to +85°C.

Applications

* High voltage current shunt sensing

* Programmable logic controllers

* Analog input front end signal conditioning

+5 V, +10 V, ±5 V, ±10 V, and 4 to 20 mA

* Isolation Sensor signal conditioning

* Power supply monitoring

* Electrohydraulic controls

* Motor controls

* High common-mode input voltage range

±120 V at VS = ±15 V

* Gain range 0.1 to 100

* Operating temperature range:

−40°C to +85°C

* Supply voltage range

Dual supply: ±2.25 V to ±18 V

Single supply: 4.5 V to 36 V

* Excellent ac and dc performance

* Offset temperature stability RTI: 10 μV/°C maximum

* Offset: ±1.5 V mV maximum

* CMRR RTI: 75 dB minimum, dc to 500 Hz,

G = +1