The LTC6803 is specifically designed for hybrid and electric vehicles (HEVs and EVs), as well as other high-voltage, high-performance battery systems. This integrated battery monitoring IC features a 12-bit ADC, a precision voltage reference, a high-voltage input multiplexer, and a serial interface. Each LTC6803 can monitor up to 12 individual battery cells connected in series. Its unique architecture allows multiple LTC6803 devices to be connected in series without the need for optocouplers or isolators, making it ideal for long battery strings where accurate cell-by-cell voltage monitoring is essential.
The LTC6803 series chip can measure up to 12 battery voltages in series, completing full cell voltage detection within 13ms. It offers an overall measurement accuracy of less than 0.25%, along with strong electromagnetic compatibility and low power consumption. In this application, two LTC6803-3 chips are used to monitor 24 series-connected batteries.
**First, the system operation**
The ATMEGA128 microcontroller reads the 24-channel voltage data from the LTC6803-3 via the SPI bus. It also collects battery temperature using an ADC and sends the information to the control board through the SJA1000 CAN controller. Once the control board receives the data, it processes the information and controls the balancing board accordingly.
**Second, the system hardware design**
**2.1 Voltage acquisition**
The LTC6803 is a battery monitoring IC developed by Linear Technology, an improved version of the LTC6802 series. It includes a 12-bit ADC and a precision voltage reference. The device can measure up to 12 battery cells connected in series, with a common-mode input voltage of up to 60V. It supports both series and parallel configurations for high-voltage applications. Each battery input has an associated MOSFET switch that enables discharging of overcharged cells. The MCU can read data from the LTC6803 via the SPI bus and control the MOSFETs to achieve cell balancing.
To protect the LTC6803's voltage acquisition pins and prevent overvoltage, a voltage regulator is connected in parallel at each cell input. An RC filter is also added before each voltage acquisition pin to reduce high-frequency interference, ensuring accurate voltage readings.
**2.1.1 Zener Diode Selection**
Since the LTC6803 has an internal 12V regulator, the external voltage regulator should be set below 12V. Considering potential open-circuit conditions in adjacent batteries, it is recommended to choose a Zener diode with a breakdown voltage more than twice the nominal battery voltage. This paper suggests a range of 7.5–9V.
**2.1.2 RC Filter Circuit Selection**
Larger RC values provide better filtering and improved surge resistance but may slightly reduce measurement accuracy. In environments with significant interference, increasing the resistor value in the RC filter is advisable.
**2.2 SPI Communication Loop**
The ADUM3401 digital isolation optocoupler is used to enable communication between the MCU and the LTC6803. It offers enhanced ESD protection and consumes 1.4mA at 2Mbps. With four isolated signal channels, it uses iCoupler technology for isolation. The ADUM3401 is powered by the VREG of the LTC1603. It’s important to note that the SDO output of the LTC6803 requires a pull-up resistor; otherwise, it will not function properly. When multiple SPI communications are present on the MCU side, the SCK and MOSI signals can be shared, but SS and MISO signals cannot.
**Third, system software design**
The software flow for the LTC6803 begins with the chip entering standby mode. It must first be initialized, then a command is sent to start the ADC. It is important to note that the LTC6803 adds a CRC check for data transmission, which is an improvement over the LTC6802.
**Fourth, test results**
**4.1 LTC6803 Accuracy Test**
According to the data in Table 1, the LTC6803 demonstrates high accuracy. The maximum error is 0.449% at a 3.8V measurement, slightly higher than the 0.25% specified in the manual but still acceptable for most applications. At lower voltages, such as 0.8V, the error increases to 0.732%. Additionally, there are minor variations between different chips, particularly between high and low channel measurements. A large input impedance can also lead to measurement errors, so users should be mindful of this during real-world implementation.
**4.3 Type Test**
The LTC6803-3 acquisition system was tested under various environmental conditions, including high and low temperatures, damp heat, smoke, and vibration. After testing, the LTC6803-3 operated normally, confirming its excellent environmental adaptability.
**Conclusion**
This article presents a lithium battery monitoring system based on ATMEL’s ATMEGA128 and Linear’s LTC6803-3. The system is capable of measuring the voltage of 24 individual cells and uploading the data to a control module via CAN. After practical testing, the system achieved ±20mV voltage accuracy and demonstrated stable and reliable performance, highlighting its significant application value in modern battery management systems.
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