Battery-Management IC Sees Inside Cells with 2-mV Accuracy

A lithium-ion (Li-ion) battery pack can consist of hundreds or even thousands of electrochemical cells that are highly sensitive to both manufacturing variations and real-world operating conditions. On top of impurities or inconsistencies in production, cells may be influenced by electrical fluctuations during charging and discharging; heat, cold, and other environmental conditions; and mechanical stress such as vibrations and pressure.

To maximize safety and longevity, electric vehicles (EVs) and other systems rely on a battery-management system (BMS) to monitor conditions down to the cell level, which also ultimately helps with extending runtime.

The BMS keeps tabs on the voltage and current of each cell in real-time to keep them operating within a safe operating area (SOA). By monitoring these parameters, it helps prevent dangerous conditions such as overcharging and overheating, both of which can damage the battery or result in thermal runaway.

In addition, the BMS performs cell balancing to ensure cells charge and discharge uniformly, boosting runtime. Without it, cells tend to charge and discharge unevenly, requiring additional safety margins that can reduce usable capacity.

New BMIC Handles Up to 14 Battery Cells

STMicroelectronics’ latest battery-management IC brings together all of the main functions for cell monitoring. The L9963F can measure the voltages of up to 14 battery cells and the current of the entire set, with fully synchronized voltage and current sampling. While a single device can be deployed in 48- and 96-V battery packs, it’s also possible to stack several together to monitor larger ones, scaling up to as many as 31 modules and 434 series-connected cells for EVs and battery energy storage systems (BESS).

The automotive-grade chip integrates a 16-bit analog-to-digital converter (ADC) to measure cell voltages with a maximum error of ±2 mV and uses coulomb counting to monitor current at the pack level, enabling pack overcurrent detection. This assists with one of the most critical and technically challenging functions in the BMS: estimating both the state of charge (SOC), which is the remaining runtime of the battery, and the state of health (SOH), which measures the battery’s aging and remaining capacity relative to what it was in new condition.

The new device’s fully synchronized current and voltage sampling doesn’t experience any desynchronization delay between samples. The coordinated current and voltage sampling works across larger battery packs, too.

When daisy-chained, the chips use a 2.66-Mb/s isolated serial interface to communicate, with a latency of only 4 µs between the first and last L9963F. With nine general-purpose I/O (GPIO) pins and a Serial Peripheral Interface (SPI) to interact with the main MCU, it also features a complete set of fault-detection and notification functions.

For safety-critical systems, the IC incorporates a fully redundant cell-measurement path with ADC swap, supporting limp-home operation. The L9963F meets the ISO 26262 standard for functional safety, and it’s ASIL-D-ready.

The chip supports cell-balancing current up to 200 mA. ST said it integrates drivers used to control cell-balancing MOSFETs, and it’s able to keep them active for a short time after entering low-power operation. This silent-balancing mode maintains protection while taking the least possible energy from the battery. The IC can be powered by same battery being monitored and integrates circuitry to generate stable internal references and ensure measurement precision, including a voltage regulator and bootstrap circuit.

The L9963F brings across-the-board improvements over the industry-proven L9963E. But it comes in the same 10- × 10-mm TQFP64 package, so it serves as a drop-in replacement requiring no hardware or software changes. Pricing starts at $4.60 apiece for orders of 1,000 units.