BMW is using the AS8510, an integrated automotive data acquisition front-end integrated circuit (IC) from ams AG, a leading provider of high performance analog ICs and sensors, to provide extremely accurate battery voltage and current measurements in its i3 electric vehicles (EVs).
The BMW i3 model in volume production today includes an AS8510 in the battery sensor. The battery management system (BMS) monitors battery voltage and battery current of the 400V li-ion battery powering the cars’ electric motors, and ensures the functional safety of the vehicle’s battery systems.
|Block diagram of the AS8510. Click to enlarge.|
Optimization of energy storage and battery life are essential for EVs in order to provide customers with sufficient range and reliability. Accurate current and voltage measurements enable the BMS to make a highly accurate calculation of a li-ion battery’s State of Charge (SOC). The driver benefits from an accurate estimation of the range the vehicle can cover before the battery is completely discharged.
When backed by a special calibration scheme, the sensor system in the BMS is able to measure current to an accuracy of just ±0.5% and voltage to an accuracy of better than ±0.1% over the full operating temperature range of the AS8510 (-40°C to +125°C) and over life time.
Features of the AS8510 that eased the task of designing the i series’ current and voltage measurement system include its zero-offset architecture, low noise, high linearity, multi-channel architecture and low drift.
The AS8510 provides integrated data acquisition front ends, which include two independent 16-bit sigma-delta ADCs. Measuring current across a shunt resistor in one channel over a range from a few milliamps up to 1kA, it provides a digital output via a serial peripheral interface. Through the second channel it can capture three different voltage sources simultaneously with current samples.
The AS8510 Data Acquisition is tailored to measure accurately battery current from mA range up to kA range in combination with a 100 µOhm shunt resistor connected in series with the battery rail. Through the second measurement channel it enables capture of either battery voltage synchronous with the current or to measure the analog output of an internal or external temperature sensor.
The AS8510 is fully compliant with the AEC-Q100 standard (Automotive Electronics Council stress qualification for integrated circuits). The device supports the functional safety compliance efforts of car manufacturers in line with the requirements of the ISO 26262 standard.
The techniques for monitoring the State Of Charge (SOC) and the State Of Health (SOH) in electric vehicle batteries are constantly being refined and improved, and BMW has set a new benchmark in battery management system design in the new i3 model. ams is proud to have supported BMW’s advanced implementation of ultra-accurate battery parameter measurement in the demanding environment of a vehicle drivetrain.—Bernd Gessner, Vice-President and General Manager of the automotive business unit at ams
Austria-based ams is a leading designer and manufacturer of sensor and analog solutions including light sensor and controller ICs. Its products are aimed at applications which require extreme precision, accuracy, dynamic range, sensitivity, and ultra-low power consumption. ams’ product range includes sensors, sensor interfaces, power management ICs and wireless ICs for customers in the consumer, industrial, medical, mobile communications and automotive markets.