Nuvoton puts impedance measurement inside a 26-cell battery monitor

Nuvoton Technology Corporation Japan has developed a 26-cell battery-monitoring IC that adds electrochemical impedance spectroscopy to conventional voltage, current and temperature monitoring.

Samples of the KA85010UA are scheduled to become available in January 2027. The device is intended for electric vehicles, large energy-storage systems and equipment used to assess batteries for reuse.

Electrochemical impedance spectroscopy, or EIS, applies a small alternating current to a battery and measures the resulting voltage response. Changes in impedance across different frequencies can provide information about processes taking place inside the cell.

Nuvoton says this can support estimates of state of health and internal temperature, as well as the identification of developing cell abnormalities. The measurements still need to be interpreted in the context of the cell chemistry, operating conditions and application.

Moving EIS out of the laboratory

EIS has traditionally required dedicated test equipment. Integrating the measurement function into a battery-monitoring IC could allow impedance data to be collected while a battery is installed and operating.

That is not simply a matter of adding another measurement channel. Generating the test current can consume power and produce heat, while switching noise and the battery’s operating state can affect the quality of the resulting data.

Nuvoton’s design uses two FETs and an inductor to circulate the alternating measurement current. This replaces a resistive method in which more of the energy is dissipated as heat.

The company reports a reduction of approximately 93% in both power loss and PCB temperature rise when compared with its conventional resistor-based method.

Those figures were obtained under defined company test conditions. The power-loss comparison used a total voltage of 72 V and a superimposed current of 1.5 A. The PCB temperature comparison used a 60 V pack and a 0.7 A measurement current.

The results should not therefore be treated as a guaranteed reduction across every pack architecture or measurement setting.

Data still needs interpretation

The KA85010UA is designed to gather impedance information, but the measurement alone does not provide a complete battery diagnosis.

Nuvoton is also offering analysis algorithms and implementation support. The company says this will cover measurement setup, data organisation, state-of-health and temperature estimation, abnormality detection and integration into the finished application.

It points to joint work with research institutions and vehicle manufacturers, including measurement comparisons published with Japan’s AIST Group. Nuvoton says its results showed a high level of agreement with dedicated EIS equipment and the 1 kHz internal-resistance measurement referenced by IEC 62620 under its stated test conditions.

Developers will still need to validate the algorithms against their own cell chemistry, pack construction, temperature range, ageing profile and fault cases. A model trained or calibrated for one type of cell cannot automatically be assumed to describe another.

For buyers, the January 2027 sampling date is also important. Nuvoton has not yet stated pricing, production availability or the qualification status that will apply when samples are released.

The significant change is the attempt to bring a laboratory diagnostic technique into the installed battery system. Its practical value will depend on whether developers can turn the additional measurement data into repeatable decisions about safety, maintenance and remaining life.