Electrochemical Impedance Measurement Module

Lithium batteries are widely applied across three main fields: energy storage, consumer electronics, and electric power. These applications range from mobile phones, laptops, and electric bicycles to electric vehicles, integrated solar-charging-storage systems, and portable energy storage devices for both consumer and industrial products. Over time, battery aging leads to performance degradation and irreversible changes in chemical composition, resulting in reduced capacity and increased internal resistance.

Electrochemical Impedance Spectroscopy (EIS) is a non-destructive method for parameter measurement and an effective technique for assessing battery dynamic behavior. By detecting increased battery impedance, EIS can determine the state of health (SOH) of a battery, helping to predict when replacement may be necessary.

The highly integrated AD5941 is a system-on-chip (SoC) designed for high-precision, low-power portable applications that utilize electrochemical measurement techniques. It integrates a high-precision analog front end (AFE), a high-accuracy excitation loop, and a 16-bit SAR ADC measurement channel, among other components. To facilitate the evaluation of the AD5941's EIS performance and accelerate product development, Excelpoint under WPG Holdings has designed the Electrochemical Impedance Spectroscopy Measurement Module for Batteries (EPSH-EIS5941-V1.0). This module supports both fixed-frequency and frequency-sweep modes. Its high integration and cost-effectiveness make it particularly suitable for compact handheld battery internal resistance testers.

The highly integrated AD5941 features a built-in waveform generator, a high-speed DAC (HSDAC), and an excitation amplifier to produce sinusoidal excitation signals. These signals are applied to the battery via the CE0 pin and an external Darlington transistor. The output is processed through an ADG636, amplified by an AD8694, and then fed into the AD5941's ADC. The device's built-in Discrete Fourier Transform (DFT) hardware acceleration engine performs DFT on the ADC data, generating real and imaginary components that are stored in a FIFO. The data is transmitted to an MCU and uploaded to a PC via USB. The accompanying GUI software displays the battery's impedance and the corresponding Nyquist plot. A reference resistor (RCAL) calibration method is used to eliminate measurement errors and enhance accuracy.