Battery fuel gauge ICs do more: monitor cells, assess results, judge trends, implement high-end security

October 24, 2016

Bakul Damle, 
Director of Mobile Power, Maxim Integrated By: Bakul Damle
Director of Mobile Power, Maxim Integrated

 

Today's portable devices – smartphones, laptop PCs, medical equipment, instrumentation, and still/video cameras, to cite a few – are extraordinarily dependent on their high-capacity, lightweight, rechargeable battery cells and packs. To be used to their fullest extent while delivering safe, reliable, and optimum performance, these energy reservoirs need much more than a simple measurement of their terminal voltage and current flows. Note that this level of sophistication is in sharp contrast to the situation of the traditional venerable lead-acid battery used in automobiles and other applications, for which the terminal voltage is usually the only parameter measured.

The battery-management situation is especially critical with cells that have high energy densities such as those using lithium-based chemistries. If there's even a tiny defect in the battery (it happens), or the charging/discharging is not managed “just right”, the consequence can be overheating, smoke, fire, or even explosion. This is illustrated by the initial problems ranging from the huge battery assemblies in the Boeing 787 Dreamliner down to the far, far smaller battery of smartphones.

It’s easy to say that the batteries need better monitoring and management, but what does that actually mean? It takes a combination of basic voltage, current, and temperature data feeding sophisticated algorithms, plus knowledge about the characteristics of these batteries in general, and learned experience of the specific pack being monitored. Keep in mind that while batteries are mass-produced components, each battery is somewhat unique with its own personality based on manufacturing variations, as well as usage patterns. A good battery-management solution takes all of these factors into account.

There’s another challenge that is peculiar to battery packs: the risks due to use of substandard counterfeits (clones) in the supply chain, either from the OEM directly or, more likely, from the replacements that are available at attractive prices. Many of these do not meet the needed quality standards of materials and construction at first, and so pose risks for substandard performance and even worse (again, smoke, fire, explosion). To the user, however, they seem OK – at least at first – and then the problems crop up. Thus, a successful, reliable, and safe battery installation requires not only data collection, analysis, and anticipation, but also some form of secure authentication to prove to the end product that the pack is legitimate.

Meeting all these needs is where the ModelGauge™ m5 portfolio of MAX17201/MAX17205 and MAX17211/MAX17215 pack-side fuel-gauge ICs makes a major difference. It measures parameters of voltage, current, and temperature of a battery pack (comprised of single or multiple cells). It then uses the data to provide the insight needed not only for intelligent, accurate fuel gauging but also the information needed to assess the health of the battery pack and future potential (pun intended) safety issues. In addition, they provide advanced security against clones via SHA-256 cryptography for authentication (with a 160-bit secret key).

Modelgauge m5

The ModelGauge m5 fuel gauges include a sophisticated algorithm that converts raw measurements of battery voltage, current, and temperature into accurate state-of-charge (SOC%), absolute capacity (mAhr), time-to-empty, and time-to-full (while charging) numbers. The robust algorithm detects the smallest changes in the capacity of the battery to more accurately predict how long the battery will last before the capacity degrades rapidly.

There is no need to reset to track battery usage correctly, as it learns capacity without the battery going to full, empty, or relaxed state. Temperature-measurement inputs include its own die reading as well as two external thermistors. By combining all these factors, the algorithm eliminates errors when cells are approaching empty voltage as well as Coulomb-counter drift, and compensates for changes in current, temperature, and even battery age.

Using these battery-management ICs greatly maximizes battery performance, and basic safety and security of battery management, but does so with very high level of confidence. Given today's headlines, cost of recalls, and time-to-market delays due to issues related to rechargeable batteries, this level of management and protection is necessary; the only question is what it takes to get there. Using the ICs in the ModelGauge m5 portfolio means the challenge is greatly simplified, while the resulting depth of coverage and protection is greatly extended.