Cover story
Figure 2: Typical hookup of an LTC2949 floating EV battery monitor in high-side current sense configuration. Power for the LTC2949 is supplied via the LT8301 flyback with VCC
positive battery terminal
connected to the
a physical layer adaptation of the standard chip-level SPI that unleashes the full potential of cost-effective distributed-pack architectures. Designed for high voltage and high noise systems, isoSPI provides safe and robust information transfer of up to 1Mbps over up to 100 meters of cable, using only a single twisted pair cable and a simple pulse transformer, at low cost. Figure 3 shows how the LTC2949 leverages isoSPI, along with the LTC6811-1, as the last element in a daisy chain or in an addressable parallel configuration.
Conclusion
of current, voltage, power and temperature data, the bus and host can spend clock cycles on other tasks, instead of continuously polling the LTC2949. To detect and store the minimum and maximum values, an alert can be issued if any user-defined thresholds are exceeded — again, releasing the host controller and bus from polling duties. An overflow alert can get generated after a specified amount of energy or charge has been delivered, or when a preset amount of time has elapsed.
To ensure monitoring accuracy, the LTC2949 provides programmable gain correction factors to compensate for the tolerances of measurement components: two for shunt resistors, a battery voltage divider, and four multiplexed inputs. These
correction factors can be stored in external EEPROM to enable a modular approach to factory calibration of battery packs. Moreover, the LTC2949 can linearise temperature readings of up to two external NTC thermistors by solving Steinhart-Hart equations with programmable coefficients; these readings can then be used to automatically temperature- compensate shunt resistor readings. By continuously compensating for both tolerance and temperature effects, not only is monitoring accuracy enhanced, but lower cost external components can be used.
A standard SPI interface is present on the LTC2949 for direct MCU connection. ADI’s proprietary isoSPI interface is also present. isoSPI is
To stay competitive, system designers need to keep a close eye on both battery and BMS technologies, which profoundly affect the end- user experience. The LTC2949 easily addresses multiple stack monitoring topologies and configurations. At practically any voltage and any current level, it enables high performance, safe, flexible and reliable battery management systems. Accurate assessments of battery SOH and SOC are immediately available via accurate readings of current, voltage, power, energy, charge, temperature and time. Key minimums, maximums and alerts can be measured, calculated and reported over a bulletproof isoSPI interface. This reduces the requirement for host resources, bus design and testing, and software design. Some of the digital features include a multiplier, accumulator, min/max registers, configurable alerts, and external component tolerance/temperature compensation. Independently or with any LTC681x multicell battery monitor, the LTC2949 addresses a critical need for next-generation EV BMS while meeting strict AEC-Q100 guidelines and ISO 26262 safety standards.
Figure 3: LTC2949 isoSPI configurations
Analog Devices UK Tel: 01932 358530
www.analog.com
08 February 2021
www.electronicsworld.co.uk
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