Integrated into battery management systems (BMS), an analog front end (AFE) digitizes and processes key inputs to ensure safe and efficient operation. While AFEs play a crucial role in electric vehicle (EV) Lithium-ion (Li-ion) battery traction packs, they are also used in other applications, such as high-voltage data acquisition (DAQ) systems, uninterruptible power supplies (UPS), and energy storage units. This article reviews core BMS specifications, highlighting the primary functions and features of AFEs alongside other critical BMS components. It also spotlights semiconductor companies that provide vital BMS components, from Analog Devices and Infineon to Texas Instruments (TI), Renesas, and others.

Exploring key BMS components

Often implemented on a printed circuit board (PCB), a BMS (Figure 1) typically comprises an AFE, a battery management integrated circuit (IC), and an embedded microprocessor (MPU) that runs embedded software. Some highly integrated solutions combine two or more of these functions into a single chip, while specific BMS designs may include additional specialized modules beyond these core elements, such as battery protection circuits, cell balancing circuitry, and communication modules.

The BMS uses real-time data and algorithms to precisely monitor and control voltage, current, and temperature, activating short circuits, overcurrents, and various thermal protection measures as needed. It also facilitates external data communication between battery packs and individual cells, efficiently coordinating management functions and delivering comprehensive diagnostics.

AFEs are the front-end analog interface between the battery cells and digital control systems. They convert analog inputs into digital signals and typically connect to other BMS components through a Serial Peripheral Interface (SPI) or Inter-Integrated Circuit (I²C).

Using data provided by the AFE (Figure 2), the BMS accurately determines battery state of charge (SOC), state of health (SOH), and state of power (SOP), optimizing battery life and generating precise range predictions for EVs. Data gathered by the AFE also helps other EV systems maximize torque, acceleration, and regenerative braking. Additionally, AFEs improve data accuracy and system reliability in high-voltage DAQs, ensure seamless power transitions in UPS systems, and facilitate efficient energy distribution in large-scale energy storage units.

Understanding the core functionality of BMS AFEs

AFEs perform various functions, such as signal amplification, filtering, level adjustment, and analog-to-digital (ADC) conversion. Temperature input sensors monitor both individual cells and overall pack thermal levels, providing critical data for thermal management and safety systems. ADCs accurately convert the measured voltage, current, and temperature of individual battery cells into digital data.

Although some AFEs measure battery pack current and voltage, dedicated current sensing circuits or shunt resistors often manage or supplement this function. AFEs can be daisy-chained to manage large cell counts, with some chips supporting the simultaneous monitoring of 16 or more cells.

In addition to temperature sensors and ADCs, key AFE components can include:

• High-voltage multiplexers: switches between different cell voltage inputs to efficiently and sequentially monitor multiple cells.
• Current sense amplifier: this amplifier assists in measuring battery pack current, often working in conjunction with shunt resistors and providing variable gain to accommodate different sense resistor values.
• Cell balancing circuitry: integrates FETs or other components to enable cell balancing, typically handling 50-200mA per cell.
• Low-voltage regulator: provides stable power, often at 3.3V, for associated circuitry.
• Safety and emergency circuitry: detects dangerous conditions such as overvoltage, undervoltage, and overcurrent.

AFEs also feature specialized circuits for interfacing with temperature sensors, including switchable bias outputs for thermistors and comparators with adjustable thresholds for detecting overcurrent conditions. High-precision, low-drift voltage references are typically integrated within these devices to provide a stable voltage baseline and ensure accurate ADC conversions.

Many AFEs are designed to operate reliably in noisy and demanding conditions and meet stringent automotive requirements, such as Automotive Safety Integrity Level (ASIL), AEC-Q100, ISO 26262, and IEC 61508. Importantly, specific features, capabilities, and configurations can vary significantly between different BMS manufacturers.

AFE-integrated battery management ICs

Many semiconductor companies include AFE functionality in their battery management ICs, providing essential monitoring, protection, and communication capabilities within the BMS architecture.

For example, Infineon offers the TLE9012DQU, Analog Devices (ADI) provides the ADBMS series, Texas Instruments (TI) features the BQ and AFE families, STMicroelectronics (ST) supplies the L9963E, and Eberspaecher Vecture sells the V04246. Similarly, NXP integrates AFE functionality within its battery management IC offerings, including the MC33771C. At the same time, Renesas supplies a range of battery front-end ICs, such as the ISL series for automotive applications and the RAA family for high-cell count and high-voltage systems.

Summary

Integrated into the BMS, AFEs digitize and process critical inputs such as temperature, current, and voltage to ensure the safe and efficient operation of EVs, DAQs, UPS systems, and energy storage units. AFEs perform various functions, including signal amplification, filtering, level adjustment, and ADC conversion. Many semiconductor companies include AFE functionality in their battery management ICs, targeting a wide range of verticals with comprehensive capabilities.

References

What is the Analog Front End (AFE)?, MaxKGo
Fundamental Understanding of Battery Management System, Microchip
Battery Management System Tutorial, Renesas
Why is a Lithium-ion Battery BMS Required for Dedicated AFE for
Voltage Sensing?, Exide Energy Solutions
Crucial Role of Analog Front Ends, Creating Bridges to the Digital World, AVNet
BMS Distributed Analog Front End (AFE), Eberspaecher-Vecture
Energy Storage Systems: How to Easily and Safely Manage Your Battery Pack, Analog Devices
Battery management systems (BMS), Infineon