The LTC6804 is the third-generation multi-cell battery monitor introduced by Linear Technology in 2012. It is capable of measuring the voltage of up to 12 series-connected batteries almost simultaneously, with a lower overall measurement error compared to its predecessor, the LTC6803. This article presents a battery management system (BMS) design that utilizes the LTC6804 along with a thermal resistance temperature sensor for multi-channel temperature acquisition. The system integrates an STM32F103 microcontroller to manage and monitor 24 individual battery cells (using two LTC6804 devices) and collect temperature data from 16 channels, while also supporting CAN bus communication.
The paper outlines the design in two main sections: voltage and temperature acquisition, and control communication.
**1. Voltage and Temperature Acquisition**
The voltage and temperature acquisition module of the BMS consists of two LTC6804 ICs, two LTC1380 multiplexer chips (each with 8 channels), and one LTC6820 communication chip connected to the ECU. For the LTC6804-1 configuration, multiple devices are daisy-chained together, with one master device communicating with the microcontroller. In contrast, the LTC6804-2 uses parallel connections, where each device is individually addressed. This article focuses on the LTC6804-1 setup. These ICs communicate via the isoSPI protocol, which allows for reliable data transfer even in noisy environments. The use of isolation transformers and twisted pair cables ensures strong electromagnetic interference (EMI) immunity, enabling a single microcontroller to manage multiple LTC6804 nodes efficiently. To enhance system reliability, the design includes redundant control mechanisms, ensuring that even if one node fails, the microcontroller can still maintain control over the rest of the system. Communication between the microcontroller and the BMS modules is facilitated through the internal CAN bus.
**1.1 Introduction to LTC6804**
The LTC6804 is a highly integrated battery monitoring IC that supports 3 to 12 series-connected batteries, with a minimum of three cells required to provide a bias voltage of at least 11V. Its stacked architecture allows for scalability, making it suitable for systems with hundreds of batteries. The chip features an embedded Zener voltage reference, a third-order noise filtering ADC, and a 16-bit resolution for cell voltage measurements, achieving accuracy better than 0.04%. It can measure all cells in just 290 microseconds and includes passive charge balancing capabilities to ensure uniform cell performance.
**1.2 Introduction to LTC6820**
The LTC6820 provides isolated SPI communication between two devices using a single twisted pair connection. It converts the standard four-wire SPI interface from the MCU into an isoSPI signal, using an isolation transformer and twisted pair for improved common-mode rejection and electrical isolation. This makes it ideal for applications requiring high reliability and safety. The isoSPI bus uses PULSE HX1188NL isolation transformers, each containing two isolation transformers with a center tap and a common-mode choke, ensuring robust and safe communication across isolated circuits.
**1.3 Temperature Acquisition with LTC1380**
To enable multi-channel temperature monitoring, the system combines NTC thermistors with the LTC1380 MUX circuit. The thermistor is connected in series with a precision resistor, and the voltage across the thermistor is measured after being divided by the reference voltage provided by the LTC6804. The MUX selects the appropriate channel, and the resulting voltage is processed through a proportional amplifier before being converted into a temperature reading. This approach ensures accurate and reliable temperature data collection across multiple battery cells.
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