A battery monitoring IC uses EIS to check cell health, detect abnormalities, estimate lifetime, and reduce heat during measurements.
Nuvoton Technology will begin providing samples of the KA85010UA, a 26-cell battery monitoring IC with built-in electrochemical impedance spectroscopy (EIS). The IC uses EIS to detect changes inside battery cells for battery degradation diagnosis, state-of-health (SOH) estimation, lifetime prediction, and early detection of abnormal conditions. It uses an inductor-based EIS measurement method that the company says reduces PCB temperature rise by approximately 93% compared with a conventional resistor-based approach.
EIS applies an alternating current to a battery and measures its voltage and current response to calculate impedance. Changes at different frequencies can provide information about different parts of a cell. High-frequency measurements can indicate changes in terminals, wiring, and electrolyte, while mid-frequency measurements provide information about the negative electrode. Low-frequency measurements can indicate changes associated with the positive electrode and internal reactions.
The KA85010UA integrates this measurement capability into the battery monitoring IC, allowing EIS measurements within a battery system without dedicated laboratory equipment. Nuvoton says measurements can be performed during battery operation, charging, and rest.
The company compared measurements from the IC with dedicated EIS equipment and 1 kHz alternating-current internal-resistance measurements specified in IEC 62620 under its evaluation conditions. Nuvoton reported a high level of agreement. The results were also published in an IEEE paper based on joint research with the AIST Group.
The IC’s EIS circuit uses two field-effect transistors (FETs) to control current direction while energy stored in an inductor is circulated to generate the alternating measurement current. This avoids the heat generated when several amperes are passed through a resistor in conventional methods.
In company evaluations, the inductor-based method reduced power loss and PCB temperature rise by approximately 93%. One test used a total voltage of 72 V with a superimposed current of 1.5 A, while another used a pack voltage of 60 V with a superimposed current of 0.7 A.
The IC is intended for battery-system developers working on applications such as automotive battery packs and energy storage systems.
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