How to Increase Safety of Automotive Li+ Battery Packs

October 8, 2019

Tamer Kira  By: Tamer Kira
 Executive Director, Automotive Business Unit, Maxim Integrated 


Nerves get rattled with every headline about electric vehicle (EV) battery fires. But the risk of a fire or explosion for EVs is actually similar or potentially a little lower than such a risk for gas or diesel-fueled vehicles, according to a 2017 report commissioned by the U.S. National Highway Traffic Safety Administration. In EVs as well as hybrids, the lithium-ion battery is the workhorse, keeping the vehicle running smoothly, safely, and efficiently. So it's essential to carefully manage the voltages across the hundreds or even thousands of cells inside each vehicle's battery pack. Overvoltage and undervoltage conditions, for example, can weaken performance or, worse, lead to some catastrophic failure.

Delivering optimal battery performance calls for precise voltage and temperature measurements. Optimal battery performance, in turn, can extend the life of the battery as well as the driving range of the vehicle. Considering how noisy a vehicle environment is, however, obtaining accurate measurements is no easy feat. Yet, given that the International Energy Agency projects the volume of EVs on the road globally to grow from 3 million to 125 million by 20301, the need for an effective solution to this challenge will only become more critical.

Electric VehicleAn ASIL D-compliant battery management solution can manage voltages in a way that drives greater efficiency and higher safety of the battery packs for electric vehicles.

ASIL D Compliance for Highest Level of Safety

A battery management system that is fast and accurate fits the bill, though there are different architectural types to consider. An isolated controller area network (CAN) architecture, based on a star configuration, is robust, but comes with high bill of materials (BOM) costs and relatively slow communication speeds. By comparison, a reliable, robust daisy-chain architecture provides faster, yet reliable, communication at a lower cost.

Another useful feature to look for when evaluating battery management systems is automated cell balancing, which minimizes the manual effort (coding, etc.) that would otherwise be required. Some level of flexibility in supporting different cell pack sizes is beneficial, too. But the biggest feature to seek is ASIL D compliance, as this Automotive Safety Integrity Level represents the highest safety risk classification under ISO 26262 and, therefore, requires the most safety-critical processes and testing.

Maxim has launched a new IC in its battery management solutions portfolio that meets these criteria. The MAX17853 is the market's only battery management solution with ASIL D compliance for temperature, cell voltage, and communication. A 14-channel battery monitor IC, the MAX17853 delivers the highest level of safety with fast and accurate (+/- 2mV) voltage and temperature measurements via a SAR ADC. The SAR ADC enables it to take fast instantaneous measurements rather than running average measurements, ensuring true cell state-of-charge and state-of-health calculations.

The device is the market's only battery management system IC with a flexible architecture. Its FlexPack architecture enables one board to support multiple battery pack configurations from 8 to 14 cells. The balancing current is set via software. A fleet of cars typically involves different cell pack sizes, but with this architecture, there's no need to redo the full BOM, qualifications, or evaluations for different variants. OEMs can even increase the number of cells in parallel, with only a software modification required.

The MAX17853 enables different daisy-chain architectures, from distributive to centralized solutions. Regardless of architecture, capacitive isolation can be used to lower BOM costs without compromising the robust communication capability. You can daisy-chain up to 32 devices to manage 448 cells and monitor 192 temperatures. The device's advanced cell balancing system automatically balances each cell by voltage and/or time, minimizing the risk of overcharging and overvoltage. You won't have to set each timer or voltage separately for each cell. Its advanced diagnostics mean that the MAX17853 is smart enough to shut down the system when there's a thermal overload. A pin-selectable SPI/UART communication interface provides flexibility in communication.

Evaluate the MAX17853 for your next design with the MAX17853EVKIT, a fully assembled and tested platform for assessing the IC's features and functions.

Learn Ways to Design Safer, Smarter, Greener Cars at ELIV

If you're attending Electronics in Vehicles (ELIV) from October 16 to 17 in Bonn, Germany, be sure to visit Maxim at booth #54. See demos of our battery management solutions, including the MAX17853, as well as our Gigabit Multimedia Serial Link 2 (GMSL 2) high-speed SerDes solution. You'll also have an opportunity to register for a raffle to win a Garmin vivoactive® 3 Music (Verizon) smartwatch.

Sources

1https://www.iea.org/gevo2018/