High-power Smart Shunt Accurately Measures Current

Riedon has announced the availability of their new SSD Smart Shunt series of high-power, reinforced isolation current sensing shunts.

As a follow-up to the company’s SSA shunt series, the new digital output SSD series is a fully integrated SiP (system-in-package) incorporating a 16-bit MCU, 24-bit analog-to-digital (ADC) conversion, and flash memory, along with the current sensing element, into a single package.

 

SSD Smart Shunt current sensor. Image used courtesy of Riedon

 

With its high level of integration, the SSD series offers a plug-and-play, highly accurate current sensing solution for high-power applications (up to 1000 A) like large-scale energy storage banks, renewable energy generation infrastructure, industrial motor drives, and EV charging stations.

 

Sensor Options for Measuring High Currents

A current shunt is a resistive element placed in the current signal path that uses the linear relationship between voltage and current in a resistor (V = RI) to measure current flow. The voltage measured across the shunt resistor indicates the current passing through the element.

 

SSA current shunt uses series resistance to measure current. Image used courtesy of Riedon

 

There are many ways to measure current in a circuit. Along with shunt resistors, another common sensor for current measurement is the hall effect sensor. Hall sensors use magnetic coupling to detect current flow, so they have the advantage of not lying within the signal path. 

Since they do not present an impedance to current flow, hall effect sensors are commonly used in higher current applications (> 50 A) to minimize power losses. 

Another advantage of hall sensors is that they are inherently isolated from the high-voltage signal path through their magnetic coupling. Resistive shunts, however, require isolation to be integrated into the sensing circuitry through isolation amplifiers, modulators, or other techniques.

 

Current sensing with shunts and hall sensors. Image used courtesy of Texas Instruments

 

Despite some of the inherent advantages of hall sensors, shunt sensors, like the SSA and SSD, are increasingly in demand for high-power applications like EV onboard charging, traction inverters, and energy storage systems where more precision and accuracy are required.

Since shunt resistors are placed in the signal path and have a highly linear response, they offer better performance than hall sensors in accuracy, noise, linearity, and long-term stability.

Using highly conductive advanced materials and clever packaging integrations, like the SSD SiP, the shunt’s negative power dissipation and sensor size characteristics in high-current applications can be mitigated to take advantage of their superior precision and accuracy.

 

Comparing shunt and hall-based current sensing. Image used courtesy of Texas Instruments

 

SSD Smart Shunt Specifications

The resistance element in the SSD series is made of CuMnNi (copper, manganese, nickel) with a nickel-plated copper terminal block. The typical package footprint is 68.8 mm x 80 mm with height profiles as low as 16.4 mm and is busbar-mounted. 

According to Riedon, the SSD is smaller than other sensing options rated for similar voltage and current. 

As an integrated, digital out SiP, the SSD allows for fewer system BOM components, a smaller PCB footprint, and shorter design time with easier digital testing and system integration.

Within the series are four standard models rated 100 A, 250 A, 500 A, and 1000 A, with custom variants available on request. Sense element resistance values range from 30 µΩ to 300 µΩ, and the shunts can be used in systems with DC bus voltages as high as 1200 V for high or low side sensing. Galvanic isolation is rated to 1500 V_DC.

The SSD offers ±0.1% accuracy and linearity over the full-scale range and good long-term stability with only a 0.1% variation in output measured over 1000 hours of operation.

The sensor module is powered by an external 3.0 V to 5.5 V supply and consumes about 30 mA of load current.

Model options are available to support an RS485 or CANBus communication protocol to interface with the host system.

 

SSD supply and digital interface (CANBus). Image used courtesy of Riedon