Reference Design
Battery Management System
A complete reference design for building production-ready battery management systems with advanced cell balancing, state estimation, and comprehensive safety monitoring for EVs and energy storage.
Introduction
What This Reference Design Is About
This battery management reference design provides a complete blueprint for developing production-ready BMS solutions for electric vehicles, energy storage systems, and industrial applications. It demonstrates our proven approach to ensuring battery safety, maximizing performance, and extending battery life.
The design covers cell-level monitoring, pack-level management, thermal control, and communication interfaces—enabling safe and efficient battery operation across various chemistries and configurations.
Requirements
- Safety: Multiple protection layers with hardware and software safeguards
- Accuracy: ±2mV cell voltage, ±1% SOC estimation accuracy
- Scalability: Support for 4S to 16S configurations, expandable to 100S+
- Communication: CAN bus, isolated UART, and cloud connectivity
- Low Power: <100µA sleep current for extended standby
Recommended Architecture
Distributed master-slave architecture with clear separation of monitoring and control:
- • Master Controller: Central processing for algorithms and communication
- • Slave Modules: Distributed cell monitoring with analog front-ends
- • Current Sensor: High-precision Hall-effect and shunt sensing
- • Precharge Circuit: Controlled inrush current management
- • Isolation Barrier: Galvanic isolation for high-voltage safety
Essential Parts of This Design
- • High-precision cell voltage and temperature monitoring
- • Active and passive cell balancing circuits
- • SOC/SOH estimation with Kalman filtering
- • Overcurrent, overvoltage, and thermal protection
- • Contactor control with precharge sequencing
- • Insulation monitoring for high-voltage systems
- • Data logging and diagnostic recording
- • CAN bus communication with J1939/UDS support
This reference design serves as a customizable foundation—adapt it to your specific battery chemistry, pack configuration, and application requirements.
Hardware
Recommended Platform: Zion
Zion Platform (Xilinx Zynq-7000) is our recommended platform for advanced BMS applications requiring FPGA acceleration.
Why Zion:
- • FPGA fabric for parallel cell monitoring and fast protection
- • Dual-core ARM for algorithm processing and communication
- • Hardware timers for precise balancing control
- • Low-power modes for extended battery life
- • Flexible I/O for various AFE configurations
Key Specifications: XC7Z020 SoC, 512MB DDR3, programmable logic for custom interfaces
Essential Components to Add
Components added to baseline Zion platform:
- • Cell Monitor AFE: TI BQ76952 16-cell monitor with balancing
- • Current Sensor: LEM DHAB S/24 Hall-effect sensor (±500A)
- • Shunt Amplifier: TI INA229 for precision coulomb counting
- • Isolated CAN: ISO1042 CAN transceiver with 5kV isolation
- • Contactor Drivers: Isolated high-side drivers for main contactors
- • Precharge Circuit: MOSFET-based precharge with current limiting
- • Isolation Monitor: Bender ISOMETER for HV insulation detection
Schematic Capture & PCB Layout
Design Tools: Altium Designer with high-voltage component libraries
PCB Stack-up: 6-layer design with dedicated high-voltage isolation zones
Key Considerations:
- • Creepage and clearance for high-voltage isolation (>8mm)
- • Kelvin connections for precision current sensing
- • Temperature sensor placement near cells
- • EMC shielding for sensitive analog circuits
Regulatory Requirements
Functional Safety:
- • ISO 26262 ASIL-C for automotive applications
- • IEC 61508 SIL2 for industrial applications
Battery Safety:
- • UN38.3 transportation safety testing
- • IEC 62619 secondary lithium cells
- • UL 2580 EV battery safety
EMC: CISPR 25, ISO 11452-2 for automotive
RTOS/Operating System
Recommended OS: FreeRTOS
FreeRTOS is recommended for its deterministic real-time performance and minimal resource overhead.
Why FreeRTOS over Linux:
- • Deterministic timing for safety-critical protection
- • Minimal boot time (<100ms to operational)
- • Low memory footprint for cost optimization
- • Easier safety certification path
- • Ultra-low power sleep modes
When Linux May Be Needed
Consider Linux for:
- • Advanced data analytics and ML-based SOH prediction
- • Complex cloud connectivity with TLS/MQTT
- • Rich HMI with touchscreen displays
- • Multi-pack coordination in large ESS
Hybrid Approach: FreeRTOS on safety MCU + Linux on application processor with clear safety boundary.
Kernel Configuration
FreeRTOS Configuration:
- • Preemptive scheduling with priority inheritance
- • Static memory allocation (no heap fragmentation)
- • 1ms tick rate for timing accuracy
- • Software timers for periodic tasks
Task Priorities:
- • Protection task: Highest priority
- • Measurement task: High priority
- • SOC/SOH estimation: Medium priority
- • Communication: Low priority
Device Drivers
Custom Drivers Developed:
- • BQ76952 SPI driver with CRC validation
- • High-precision ADC driver for current sensing
- • Isolated CAN driver with J1939 support
- • EEPROM driver for calibration storage
- • Watchdog driver with safety monitoring
Real-Time Requirements: Cell measurement at 100Hz, protection response <1ms
Middleware
Recommended Middleware
Custom BMS Protocol Stack - Lightweight middleware optimized for battery system communication.
Why Custom Middleware:
- • Minimal overhead for resource-constrained MCUs
- • Purpose-built for battery-specific data flows
- • Proven reliability in production systems
- • Easy certification for safety applications
Regulatory Considerations
Protocol Standards:
- • SAE J1939 for vehicle communication
- • ISO 15118 for EV charging communication
- • CANopen for industrial applications
Data Security:
- • CRC protection for all messages
- • Message authentication for critical commands
- • Encrypted storage for calibration data
Middleware Interfaces
Cell Data Interface:
- • Cell voltage readings (16-bit)
- • Temperature sensor data
- • Balancing status and control
- • Fault flags and diagnostics
Pack Interface:
- • Pack voltage and current
- • SOC/SOH estimates
- • Contactor status and control
- • Power limits (charge/discharge)
External Interface:
- • CAN message abstraction
- • Diagnostic services (UDS)
- • Configuration parameters
- • Data logging interface
Application
Application Architecture
Bare-metal/RTOS Firmware with modular task-based architecture.
Architecture Pattern: State machine-based design with clear safety states and transitions.
Design Decision: C for safety-critical code (MISRA-C compliant), C++ for higher-level algorithms.
Core Application Modules
- • Cell Monitor: Voltage, temperature acquisition with fault detection
- • SOC Estimator: Extended Kalman Filter with coulomb counting backup
- • SOH Estimator: Capacity fade and resistance growth tracking
- • Balancer: Passive/active balancing with thermal management
- • Protection Manager: Multi-level protection with safe state control
Development Tools
Essential Tools:
- • ARM Keil MDK for firmware development
- • MATLAB/Simulink for algorithm development
- • Python for data analysis and testing
- • PCAN for CAN bus debugging
Testing Tools:
- • Battery cell simulator for HIL testing
- • Thermal chamber for environmental testing
- • Unity test framework for unit testing
Diagnostics & Security
Log Management & Debugging:
- • Event log with timestamp and fault codes
- • Lifetime statistics (cycles, Ah throughput)
- • Debug UART for development access
OTA & Security:
- • Dual-bank firmware update with rollback
- • Signed firmware with secure boot
- • Calibration data protection
Other Essential Supporting Apps
Cloud Integration
- • Fleet Monitoring: Real-time battery health across deployed units
- • Predictive Analytics: SOH prediction and maintenance scheduling
- • OTA Updates: Secure firmware updates with rollback
- • Data Lake: Historical data for warranty analysis and improvement
Desktop Applications
- • Calibration Tool: Cell balancing calibration and SOC alignment
- • Diagnostic Tool: Real-time monitoring and fault analysis
- • Configuration Tool: Parameter configuration and limits setting
- • Log Analyzer: Post-mortem analysis for field issues
Web-Based Apps
- • Fleet Dashboard: Battery health overview for fleet operators
- • Warranty Portal: Battery history for warranty claims
- • Service Portal: Field service tools and documentation
- • Analytics Dashboard: Battery performance trends and insights
Our Experience
Products Delivered
Using this reference design, we have successfully delivered:
- EV Battery Pack: 96S BMS for electric vehicle with ASIL-C certification and 10-year warranty support
- Grid Storage System: Multi-pack BMS for 1MWh energy storage with cloud monitoring
- Industrial Equipment: BMS for material handling equipment with ruggedized design
Key Achievements
±1%
SOC Accuracy
ASIL-C
Safety Rating
<1ms
Protection Response
100S+
Cell Support
Our BMS reference design has been deployed in thousands of battery packs with zero safety incidents.