Texas Instruments (TI) has developed a 28 channel battery management chip with electrochemical impedance spectroscopy (EIS) to monitor state of health, writes Nick Flaherty.

“One issue is lack of visibility into the battery cell and engineers have long struggled with gaining that visibility,” said Wenjia Liu, general manager of battery management solutions at TI.

“Only recently has EIS been practical,” she continued. “What it does is send small currents over a range of frequencies to measure the cell response. You can think of EIS as the battery’s EKG heart monitor, enabling earlier insights and predictions.”

The BQ79826Z-Q1 battery monitor determines the state of charge of up to 26 cells to within 2 mV across the whole temperature range of -40 to +125 C and 0 to 5.5 V cell voltage.

“The EIS detects potential failures from inside the cell and is the industry’s first 26 channel device,” said Bryan Burke, systems engineer for battery products at TI. “This gives more accurate state of charge estimation and real-time diagnostics. This is a new innovation for our BMS portfolio, which allows engineers to reduce the number of temperature sensors and give more accurate temperature values from inside the cell with predictive diagnostics, and detects internal cell stress earlier than ever before to identify the risk of thermal runaway.”

When a pack can have 100 to 200 cells, the 26 channel device is stackable to 128 cells and can provide significant saving on the monitors and the components that go around it in both 400 and 800 V designs. Integrated transistors provide passive balancing of cells up to 300 mA.

“We have also reduced the noise by 10 times to measure the signals. So overall, our chip is much more accurate,” said Burke.

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