Miniature isolation amplifiers for motor control

They feature increased accuracy, bandwidth and high insulation, made possible thanks to Avago's optical-isolation technology.

Based on sigma-delta analogue-to-digital converters and chopper-stabilised amplifiers, the new isolation amplifiers feature high gain accuracy, low-temperature drift, 3.3V/5V output supply operation and a wide -40C to +105C operating-temperature range.

These features are delivered in a stretched SO-8 package that has a footprint 30 per cent smaller than the standard DIP-8 package.

When mounted on a PCB, it occupies a space that is a fraction of a traditional Hall Effect or transformer-based isolation amplifier.

The series is implemented with a fully differential circuit topology with a gain accuracy of +/-0.5 per cent (ACPL-C79B), +/- one per cent (ACPL-C79A), or +/- three per cent (ACPL-C790).

Normalised gain drift is -50ppm/C.

With a 200kHz bandwidth and 1.6US response time, the ACPL-C79x captures transients during short circuit and overload conditions.

Operating from a single 5V supply, the isolation amplifier series features an excellent nonlinearity of 0.05 per cent and an SNR of 60dB.

The ACPL-C79x high common-mode transient immunity of 15kV/us provides the precision and stability needed to accurately monitor current in noisy motor-control environments.

This ensures smoother control with less 'torque ripple' in many motor-control applications.

Pending safety and regulatory approvals include: IEC/EN/DIN EN 60747-5-5: 1140V peak working insulation voltage; UL 1577: 5000Vrms / one-minute double-protection rating; and CSA: Component Acceptance Notice #5.

Widely used for motor phase and rail-current sensing, servo motor drive, switching power-supply feedback isolation, DC link voltage monitoring, inverter current sensing and switching power-supply feedback isolation, the ACPL-C97x targets industrial automation and instrumentation, renewable energy and HVAC markets.

In a typical motor-drive application, currents through a small-value current-sense resistor cause a voltage drop that is sensed by the ACPL-C79x isolation amplifier, and a differential output voltage, proportional to the current, is created on the output side of the isolation barrier.