42V Difference Amplifier

Crucial component for the next generation

Slowly, inexorably, the automobile industry approaches the target date for The Great Changeover, when the term "42 volts" enters the salesman’s vocabulary, and the serviceman’s nightmares, full time. As has been mentioned a few Januarys ago in this publication, the industry is expected to begin slowly but, eventually, all vehicles will be running with 42V electrical systems to accommodate GPS systems, electronic brakes and steering, and a slew of engine control sensors, along with many other power-hungry devices.

To this end, support systems must be prepared. More than solenoids and lighting, electronic control systems and engine computers are being designed for the new supply voltage. For such systems, Analog Devices Inc, Wilmington, MA, has developed a difference amplifier suited not only for today’s 14V and 24V automotive systems, but for the 42V environment, as well. Amplifiers, which are the primary building blocks in every analog circuit, are ubiquitous in today’s vehicles that use electro-mechanical systems to operate myriad functions, from power steering and braking systems to fuel injection and transmission control. The new amplifier, the AD8205, is a high-side current sensing solution critical to the solenoid and motor control circuits that reside within automotive systems, such as the transmission, brakes, suspension, steering, water pumps and wipers. Replacing mechanical systems with electro-mechanical systems is making cars lighter, more fuel-efficient and higher performing. In addition, devices like the AD8205 help electro-mechanical systems reduce emissions by delivering more accurate system control and efficiencies.

The AD8205 is a high-performance, single-supply difference amplifier with a wide input common mode voltage (CMV) operational range of -2V to 65V, which allows the chip to measure small differential voltages — such as across a shunt resistor — in the presence of high voltages (large CMV). Additionally, the device can survive over an input CMV range of -5V to 70V. The part’s ability to reject high, common mode voltages while measuring small differential voltages eliminates error sources commonly associated with current sensing in electro-mechanical systems.

The amplifier also is well suited for industrial applications that measure small differential voltages in the presence of high CMV. Many industrial current sensing applications, such as hydraulic systems and motor control, already require this extended CMV range. Excellent DC performance over temperature keeps errors in the measurement loop to a minimum. Offset drift is less than 20 mV/°C, and gain drift is below 30 ppm/°C (up to 125°C). The AD8205 also has very high common-mode rejection of 80 dB, which extends from DC up to 100 kHz.

The AD8205 samples in an 8-pin SOIC (small outline integrated circuit) package, specifying over the extended temperature range of -40°C to 125°C. Additionally, the AD8205 is available in die form, with an extended temperature range of -40° C to 150°C for use in higher temperature applications.

—RM