TI Rolls Out Two Battery Monitor ICs Aimed at Boosting EV Range

We kick off our coverage of the CES (Consumer Electronics Show) this week with today’s announcement from Texas Instruments (TI) of a pair of ICs aimed at maximizing the driving range of electric vehicles (EVs). CES runs January 5-8 this week in Las Vegas, NV, but CES Media Days are already underway, running yesterday and today (January 3-4).

As part of the company’s battery management systems (BMS) portfolio, TI has launched its BQ79718-Q1 battery cell monitor IC and BQ79731-Q1 battery pack monitor IC. According to the company, these ASIL D-compliant chips are vital to meeting the needs of today’s EV BMS architectures.

 

Advanced monitoring is critical for today’s EV battery management systems. Image used courtesy of Texas Instruments

 

In this article, we discuss the relationship between battery monitoring accuracy and EV range, we examine the key details of TI's new chips, and we share insights from our interview with Sam Wong, general manager for BMS at TI.

 

Why Measurement Accuracy Matters

It’s clear that widespread adoption of EVs is tied closely with vehicle range—how far an EV can drive before needing to recharge its battery system. According to TI, the most important factor in designing a BMS for an EV is to enable auto manufacturers to know the true range of a vehicle. Doing so requires accurate measurement of the battery systems.

Along those lines, TI claims its new automotive battery cell and pack monitors provide the most accurate measurement capability available. TI says its BQ79718-Q1 allows carmakers to achieve high-performance battery cell voltage measurements down to ±1 mV of open circuit voltage (OCV) accuracy.

Putting things into perspective, Wong says that TI’s previous generation of cell monitor offered an accuracy of ±3 mV. “That accuracy was very good when the whole industry was using NMC (magnesium nickel cobalt) EV batteries,” says Wong. Now the industry is switching to LFP (lithium iron phosphate) batteries. LFP batteries are up to 20% cheaper than NMC batteries, mostly because iron is a readily available metal.

 

New Trade Offs to Consider with LFP Batteries

All that said, LFP batteries have a significant drawback, says Wong. The discharging curve of an LFP device is very flat compared to an NMC battery. As shown in the table in the image below, with ±10 mV accuracy in the MMC battery pack you have to budget for a ±6 mile difference in EV range.

 

With an OCV measurement accuracy of ±1 mV, the BQ79718-Q1 enables greater effective range for EVs. Image used courtesy of Texas Instruments (Click image to enlarge)

 

“At that same ±10 mV accuracy applied to an LFP battery pack, the differential translates to ±78 miles,” says Wong. “Considering that an average EV’s range is 300, that’s a good chunk of mileage paranoia that drivers have to suffer.”

With TI’s new BQ79718-Q1’s accuracy of ±1 mV, drivers only have to face a ±15 mile uncertainty when it comes to knowing when their battery is truly in danger of running out of charge, says Wong.

 

“We all drive cars and even in a gasoline-powered car situation, we typically won't leave 5% in the gas tank before going to the gas station. So this ±15 miles gives a similar user experience for EV drivers because that translates to 5% of 300 miles.”

 

Battery Pack Monitor for BJB Systems

TI’s other new device, the BQ79731-Q1, can be used to measure divided down high voltage nodes in a battery system. The device embeds two current sense paths. It can measure voltage across fuse, contactors and check isolation voltage in battery junction box (BJB) systems.

The BQ79731-Q1 IC allows measurement of the battery pack current down to 0.05% of accuracy. Used together, the two chips provide what TI claims is the clearest picture possible to measure accurate state of charge, but also the state of health at the individual cell and pack level.

 

The BQ79731-Q1 boasts battery pack current measurement with an accuracy of 0.05%. Image used courtesy of Texas Instruments

 

Meanwhile, the devices enable voltage and current synchronization at 64 µs. According to TI, this means the EV’s BMS can do instantaneous monitoring of battery pack power. This enables a real-time snapshot of battery health, says TI.

Because of this level of synchronization, BMS designs can perform electrochemical impedance spectroscopy, which can extract info on a battery cell’s core temperature, battery aging, and the battery’s state of charge. More information is available on the datasheets for the BQ79718-Q1 and BQ79731-Q1.

 

Eval Boards and IC Packaging Specs

Automotive engineers can evaluate the battery cell monitor using TI’s BQ79718-Q1 evaluation module (BQ79718EVM-049). The 18-channel BQ79718-Q1 is provided in a tiny 10 mm × 10 mm, 64-pin thermally enhanced thin quad flat package (HTQFP).

The battery pack monitor BQ79731-Q1 also has an evaluation module (BQ79731Q1EVM-060). The BQ79731-Q1 comes in a 7 mm × 7 mm, 48-pin thermally enhanced thin quad flat package (HTQFP). All products featured for BMS are available now.

 

The Road Toward Greater Confidence in EVs

While EVs are by no means a new phenomenon, there are many hurdles that could slow their adoption. Technology changes, such as adoption of new battery chemistries like LFPs come with new tradeoffs. But those tradeoffs can be mitigated by smart EV BMS design choices. These new battery monitoring ICs perhaps represent an example of just such solutions.

At CES this week, TI is demonstrating its BMS technology featuring its new BQ79718-Q1 and BQ79731-Q1 devices. If you're at the show, you can visit them at the North Hall N115 meeting room at the Las Vegas Convention Center. Demo videos are expected to be posted today on TI’s CES 2023 page.