Automotive sensor interface helps BMW manage battery performance

September 17, 2014 // By Paul Buckley
An ams AS8510 integrated automotive sensor interface is being used to provide accurate battery voltage and current measurements in BMW's 'i3' series electric vehicles (EVs).

The BMW i3 model that is in volume production today includes an AS8510 in the battery sensor. The battery management system (BMS) monitors battery voltage and battery current of the 400 V li-ion battery powering the cars’ electric motors, and ensures the functional safety of the vehicle’s battery systems. Optimisation of energy storage and battery life are essential for EVs in order to provide customers with sufficient range and reliablity. Accurate current and voltage measurements enable the BMS to make a highly accurate calculation of a li-ion battery’s State Of Charge (SOC). This means that 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 f 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, including its zero-offset architecture, low noise, high linearity, its multi channel architecture and low drift made the task of designing the i series’ current and voltage measurement system easier than using other sensor interface architectures.

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 1 kA, 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 is fully compliant with the AEC-Q100 standard. The device supports the functional safety compliance efforts of car manufacturers in line with the requirements of the ISO26262 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