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DESIGN & PRODUCTS ANALOG & MIXED SIGNAL Fig. 4a: Voltage measurement ADC gain error Fig. 4b: Current measurement ADC gain error connected to a charge complete output of a battery charging circuit. With all of this digital functionality, someone might still ask, “Why weren’t battery profiles or capacity/SOC estimation algorithms built into the LTC2944?” The answer is simple – it all comes down to (perhaps not surprisingly) accuracy. While battery gas gauges with built-in battery profiles and algorithms may simplify designs, they are often times inadequate or irrelevant models of real world battery behavior and sloppily sacrifice SOC accuracy in the process. For example, users may be forced to work with generic charge and discharge profiles that were generated by unspecified sources or over unknown temperature ranges; exact battery chemistries may not be supported which causes another hit to SOC accuracy. The point is accurate battery modeling typically considers many variables and is complex enough that it makes sense for users to model their own battery in software in order to obtain the highest level of SOC accuracy, rather than rely on inaccurate generic built-in models. These built-in models also make battery gas gauges inflexible and difficult to reuse in designs. Put another way, it is a lot easier to make changes in software than in hardware, where changing application-specific code is much easier than swapping out a battery gas gauge that also needs to be configured. If providing all of the essential battery measurement parameters with unrivaled accuracy via a very handy I2C interface were not enough, then the high voltage capabilities is what truly sets the LTC2944 apart from other battery gas gauges in the market Fig. 4c: Temperature error vs. temperature today. The LTC2944 can be directly powered from a battery as small as 3.6V to a full blown battery stack up to 60V, addressing any application from low-power portable electronics to powerhungry electric vehicles. No need to complicate designs with additional level shifting circuitry on the supply or measurement pins – direct connections between the battery (or battery stack) and the LTC2944 is possible and drastically simplifies hardware design. Minimizing the number of external components also lowers the overall power consumption and increases accuracy since components, like resistive dividers, are not present. Conclusion Battery gas gauging is an art in itself because of the many interdependent parameters that influence SOC. Experts around the world agree that accurate coulomb counting, coupled with voltage, current and temperature readings, provide the most accurate method to estimate SOC. The LTC2944 battery gas gauge provides all of these fundamental measurements and deliberately excludes internal battery modeling, allowing users to implement their own relevant profiles and algorithms in application-specific software. Moreover, measurements and configuration registers are easily accessed over I2C, while up to 60V multicell connections can be made directly to the LTC2944. Battery gas gauging any number of batteries with any battery chemistry has never been easier or, more importantly, more accurate. Staying ahead of the design curve By Lonnie Jones Passive electronic components are an essential part of all circuit designs. The push for smaller, faster and more efficient electronic products has driven the development of electronic capacitors at an incredible rate. Since the 1960s, the volumetric efficiency of the ceramic capacitor has increased tenfold as a result of lower operating voltage requirements and manufacturing technology innovations. At the same time, the cost per microfarad has decreased by a similar proportion due to benefits of worldwide mass production. Manufacturers of passive components have continuously added value to their products by not only increasing volumetric efficiency and reducing costs, but also by introducing components such as capacitor arrays, designs with lower inductance, less microphonics, integrated resistors and inductors, and improved mechanical robustness. A simple search of passive component suppliers’ product offerings today finds an amazing 400,000+ different capacitor products, including 200,000+ ceramic capacitors. Today’s leading high-tech OEM brands continue to press passive component suppliers to expand this diverse selection. A growing segment of the electronics market has specialized needs such as higher voltage capability, higher temperature capability, lower Equivalent Series Resistance (ESR) or inductance (ESL), higher ripple current capability, pulse and surge endurance capability, and increased mechanical robustness, to Lonnie Jones is Senior Technical Associate at KEMET Corporation – www.kemet.com 30 Electronic Engineering Times Europe March 2017 www.electronics-eetimes.com


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