The importance of battery management for eCall systems



While no one wants to be in a car accident, it’s nice to know that an emergency infrastructure exists when one happens. As of April 1, 2018, any car purchased in the European Union (EU) or Iceland will have the ability to call 112 (the EU equivalent of 911) for emergency-response purposes.

The emergency call (eCall) system will contact an emergency-response operator, who will then receive the car’s position and airbag deployment status. Additionally, the operator will be able to provide verbal assistance.

Russia is developing a compatible system called ERA-GLONASS that uses its Globalnaya Navigazionnaya Sputnikovaya Sistema (GLONASS) (an alternative to GPS) to derive position information. Automakers in other countries have similar (but not legally mandated) systems. In the U.S., GM offers OnStar, Nissan offers CarWings, and Daimler offers mbrace. Brazil is developing SIMRAV for stolen-vehicle tracking Telematics and the Internet of Things are arriving to a car near you!

Because a standard battery could easily be damaged in a collision and unable to provide power to the rest of the car, the eCall system needs to be independent and fairly self-contained – and thus must rely on an independent battery. Automakers tend to use lithium-ion (Li-ion) or nickel metal-hydride (NiMH) cells for these batteries. As these cells spend most of their time full or almost full doing nothing (because the car is turned off or because accidents are infrequent), the main cause of cell discharge is actually self-discharge – Li-ion cells can discharge 20% in a year when not used.

With either Li-ion or NiMH batteries, the battery-management system has to perform several basic tasks:

  • Decide whether the battery is still usable or not
  • Decide when it’s time to charge the battery
  • Charge the battery
  • Prevent overcharging, even in case of malfunction of the charger

Li-ion cells present many advantages over NiMH cells and are becoming the cell of choice for many vehicles. But they also require more sophisticated battery management, which is where TI can help.

  • To detect whether the battery still can hold enough charge to complete a call (i.e. to compute the State of Health of the battery), eCall system designers can opt for a fuel gauge like the bq27441 for systems with single cells (1s systems) or the bq28z610 for systems with two cells in series (2s systems). A gauge will also reveal how much charge you have left in the battery (i.e. to compute the State of Charge of the battery), or in other words when it’s time to charge.
  • To facilitate charging, the bq24081-Q1 and bq2057T/bq2057W are great solutions for 1s and 2s systems, respectively. Note, however, that in automotive environments redundancy is highly valued. You do not want a malfunction to the charger – or the circuitry connected to it – to cause you to miss an overcharging (overvoltage) condition.
  • And, you guessed it, TI can help with overvoltage protection: the bq29700 for 1s systems and the bq29209-Q1 for 1s and 2s systems make protection easy.

When I drive my electric car, I entrust my life to TI battery-management parts (the bq7PL536A-Q1). Likewise, while I hope I’ll never have to use an eCall system, if I do, I definitely want to have TI battery-management parts in there.