Fast isolated current sensing for inverters and drives

September 02, 2015 // By Graham Prophet
Silicon Labs says it has the fastest-available isolated current sense amplifier in the Si8920 analogue amplifier, offering precise current shunt measurement for power control systems including industrial motor drives and inverters

The Si8920 isolated amplifier provides current shunt measurement for power control systems operating in harsh environments such as industrial motor drives, solar inverters, high-voltage power converters, uninterruptible power supplies (UPS) and electric/hybrid-electric vehicle (EV/HEV) systems.

Measuring current on high-voltage rails (up to 1200 V) with a galvanically-isolated amplifier provides critical information to the low-voltage controller that improves system response time and efficiency. The Si8920 isolated amplifier provides a differential, low-voltage input scaled for connection to current shunt resistors, enabling the controller to make precise measurements of current on high-voltage rails while maintaining electrical isolation. The device’s signal bandwidth (up to 750 kHz) ensures rapid, precise dc current measurement and accurate representation of the primary signal and harmonics.

The Si8920 isolated amplifier uses Silicon Labs’ CMOS-based isolation technology, which meets stringent UL, VDE, CQC and CSA standards, supports up to 5 kV withstand and 1200V working voltage, and offers a wider operating temperature range, better noise immunity and longer lifetimes than competing isolation technologies. The Si8920 amplifier’s 1 µV/°C offset drift ensures stable performance over diverse operating conditions.

The Si8920 provides, Silabs says, a robust, reliable isolated amplifier solution that meets the product longevity requirements of industrial automation, green energy and Internet infrastructure equipment, adding, “Many power systems feature long lifetime warranties and are expected to operate for 25 years or more in the field. Isolation often can be a point of first failure and a lifetime-limiting device in many power systems. Traditional isolators, based on optocoupler technology, suffer from limited temperature range and can degrade with the external environment. In contrast, CMOS-based isolation components such as the Si8920 isolated amplifier operate over a full industrial temperature range and can support product lifetimes of up to 100 years.”

The Si8920 isolated amplifier provides very fast response time with a 0.75 µsec signal delay across the isolation barrier, allowing power control systems to react rapidly to transient load conditions. Ultra-low signal delay