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Electric vehicles (EVs) are rolling toward the future, but the path isn’t without obstacles. Range anxiety persists—no driver wants to experience an unexpected dead battery when miles from the nearest charging station. And initial EV costs remain high in contrast to conventional internal-combustion-engine (ICE) vehicles. Fortunately, advanced semiconductors are arriving on the scene to help overcome these obstacles.
EVs are Here to Stay
Mark Ng, who leads Texas Instruments’ hybrid-EV (HEV) and EV powertrain business, sees EVs not as cars with batteries and electric motors, but rather as big electronic devices climbing the same innovation curve that has transformed communications, computing, and personal-electronics markets. Ng cites several specific innovations:
- Advanced battery-management systems (BMSs) help drivers overcome concerns about range, safety, and reliability.
- Onboard chargers deliver optimal voltages and currents to each battery cell while avoiding the overcharging or undercharging that can limit battery life.
- Gate drivers with adjustable gate-drive strength enable traction inverters to optimize energy usage based on road conditions and driving style.
- Power-management technologies provide high levels of functional safety, while sensors and microcontrollers help drivers cope with sudden hazards.
Ng adds that new technologies make EVs more affordable as manufacturers move toward zone-control architectures, integrated powertrains, wireless BMSs, and intelligent battery junction boxes.
Multiple Chemistries
New battery chemistries offer a key opportunity for EVs. Most have employed lithium-ion batteries, which require cobalt, an expensive rare-earth element. Consequently, manufacturers are investigating cobalt-free alternative chemistries, including lithium ferro (iron) phosphate (LFP).
LFP batteries, however, have a significant drawback. Unlike lithium-ion batteries, whose voltage drops steadily as they discharge, LFP batteries exhibit a minuscule voltage drop even as they approach full depletion. That characteristic makes it difficult to predict remaining driving range.
“LFP’s flat discharge rate requires a voltage measurement accuracy that’s right at the limit of what modern semiconductor technology can deliver,” said Ng.
To cite a specific number, a conventional BMS device offers a 25% uncertainty in remaining driving-range estimation for an LFP battery. Consequently, an LFP-battery-powered EV must underreport remaining range by 25% to minimize the chance of a battery dying in the middle of a journey. TI offers a BMS portfolio that includes chargers, gauges, monitors, and protection ICs that provide the precision necessary to alleviate this problem.
Ng elaborated, “Instead of telling you there are 200 miles left when you actually have 250 miles, with our chip the car might tell you that you have 230 miles left. The BMS has essentially extended your range by 30 miles, with the same charge on the same batteries.”
Accurate battery monitors find use beyond remaining driving-range indication. They’re also critical for maintaining the safety and reliability of the nearly 200 cells that typically go into an EV’s battery pack. During normal operation, a monitor can determine whether one cell is discharging faster than others, and during charging, it can tell if a cell is reaching capacity more quickly than others.
In either case, the abnormally performing cell can be switched out as necessary to prevent damage to the cell as well as maintain a suitable balance among all of the cells. In addition, monitors can look for overtemperature conditions.
“The BMS provides an elaborate monitoring network to sense the voltage, current, and temperature of each cell,” said Sam Wong, who leads a battery-monitor team at TI. “That way, we can cut a battery off from the system, or adjust the current going in or out of it.”
A specific member of TI’s BMS IC portfolio is the BQ79718-Q1 battery monitor, which complies with ISO-26262 ASIL-D functional-safety requirements and provides precise monitoring of nine to 18 cells in series (Fig. 1).
