BMS (Battery Management System) is a bridge that connects the core components of new energy vehicles with batteries and the whole vehicle. Benefiting from the development of new energy vehicles, BMS as a core component has also developed rapidly. BMS is divided into master-slave BMS and all-in-one BMS according to different control structures. Regardless of the control structure, total current sensing is essential. The current detection of the BMS is divided into the traditional Hall sensor detection method and the shunt detection method. After analysis, the current sensor solution based on shunt direct current sampling technology has lower cost and higher accuracy, and is the first choice for BMS applications in automotive and energy storage systems.
The shunt detection method has become the first choice, on the one hand, because of its high measurement accuracy and relatively low cost, and on the other hand because of its simple measurement method, less equipment, and convenience. The measurement principle is to directly measure the voltage across the shunt, and then divide the measured voltage by the resistance of the shunt according to Ohm’s law to obtain the current value in the circuit. Although the Hall sensor detection method is simple in structure, its measured value varies greatly with temperature. To this end, this article will introduce a low-cost and high-precision shunt detection solution based on Microchip MCU, CAN interface and signal conditioning platform for your reference and use.
The scheme adopts Bourns’ high current shunt CSM2F-8518-L100J32, Microchip’s MCU ATSAMC21E18A, ADC MCP3421, instrumentation amplifier MCP6N16, voltage reference MCP1501 and Microchip’s CAN interface ATA6560. The instrumentation amplifier MCP6N16 and the voltage reference MCP1501 amplify and lift the collected signal of the shunt, and then the 18-bit built-in PGA ΔΣ ADC MCP3421 converts the amplified analog signal into a digital signal, and transmits it to the Microchip MCU ATSAMC21E18A through the I2C interface, and then the MCU performs data processing. Reading, processing and calibration, Microchip’s CAN interface ATA6560 is used for data communication. In addition to BMS systems, the solution can also be used in electric and hybrid vehicles, busbar current detection and welding equipment.
The characteristics of this shunt solution: the maximum working isolation voltage can reach 560V. At room temperature, the accuracy can reach 2‰, the full-range accuracy is 5‰, the power supply wide range voltage input, the current consumption at 12V is less than 3mA, the operating temperature range is -40~125 ℃, the continuous detection current is 500A, and the maximum inrush current is 1000A (30mins). on/off).
In order to facilitate the user’s testing, calibration and application, the program also provides host computer software. The bridging tool allows users to intuitively calibrate and test the shunt scheme. The built-in Flash of the MCU supports read and write functions, and is used to simulate the function of EEPROM to store the calibrated data. There are NTC temperature sensors attached to the board and the shunt, and the user can read the temperature on the board and the shunt in real time.
After understanding the overall characteristics of this current detection scheme, we will introduce the characteristics of the core devices that make up this scheme one by one.
Let’s start with the MCU of this solution. The Microchip MCU ATSAMC21E18A features a 32-bit Cortex M0+ MCU, which can be powered by 5V. The flexible serial peripheral Sercom can be flexibly configured into UART, SPI and I2C; the built-in CAN controller supports CAN-FD, Also compatible with CAN2.0 A/B.
Its amplifier, the MCP6N16, features a self-correcting architecture that maximizes DC performance with ultra-low offset, low offset drift, and excellent common-mode and power-supply rejection, while eliminating the undesirable effects of 1/f noise, enabling full temperature range achieve ultra-high precision. The MCP6N16’s low-power CMOS process technology provides 500 kHz bandwidth while achieving low power consumption. Additionally, it features a hardware enable pin to further reduce power consumption. This low-power operation and shutdown feature requires less current for a given speed and performance, thereby extending battery life and reducing self-heating. The amplifier operates as low as 1.8V, allowing two 1.5V dry cells to consume far less power than typical, while its rail-to-rail input and output operation ensures full-range use even at low power supplies . This results in a dramatic increase in performance over the entire operating voltage range. The MCP6N16 Instrumentation Amplifier is ideal for applications requiring high performance, high accuracy combined with low power, low voltage operation, including sensor interface, signal conditioning, and stationary and portable instruments in the medical, consumer and industrial markets.
Compared to other A/D converters, the MCP3421 is ideal for a variety of high-precision analog-to-digital conversion applications that require simple design, low power consumption, and space savings. Its characteristics are mainly reflected in: fully differential input, 18-bit resolution, precise continuous self-calibration function; selectable 3.75, 15, 60 or 240SPS sampling rate for conversion; can work in continuous conversion or single conversion mode, in a single conversion It automatically enters standby mode during the idle period after conversion, which greatly reduces current consumption; the reference voltage source with 2.048V 0.05% accuracy and temperature drift of only 5ppm/℃ is integrated inside, and the programmable gain amplifier (PGA) provides 1/ 2/4/8 times gain, allowing to measure extremely small signals with high resolution, internal integrated oscillator circuit and provide I2C serial interface, etc.
“The development of the ADC market and applications requires higher resolution, higher speed and higher accuracy,” said Bryan J. Liddiard, vice president of Microchip’s Mixed and Linear Signal Products Group. Importantly, these new products meet all of these needs.”
The high voltage input integrated switching buck regulator MCP16331 operates from input voltage sources up to 50V. Integrated features include high-side switching, fixed frequency peak current mode control, internal compensation, peak current limit and over temperature protection. A complete step-down DC/DC converter power supply can be developed with minimal external components. High converter efficiency is achieved by integrating current limiting components, low resistance, high speed N-channel MOSFETs and associated driver circuits. The high switching frequency minimizes the size of external filtering components, enabling a small size solution. The MCP16331 can supply 500 mA of continuous current while regulating the output voltage to 2.0V-24V. The device integrates a high-performance Peak Current™ mode architecture that stably regulates the output voltage even during input voltage steps and output current transient conditions commonly found in power systems. The EN input is used to turn the device on and off. For brownout and load sharing applications, the input draws only a few μA when the device is off. This pin is pulled up internally, so the device will start up even if the EN pin is left floating. The output voltage can be programmed with an external resistor divider.
The automotive and industrial CAN markets continue to demand higher performance, lower power consumption and greater flexibility in cost-effective solutions. Microchip’s new family of high-speed CAN transceivers meet high performance requirements, offer the industry’s lowest standby current, and are available in a variety of small form factors. Microchip’s ATA6560/1 transceiver supports the CAN FD standard and data rates up to 5Mbits/s, providing a docking interface for the CAN protocol controller and the CAN two-wire physical bus. Compliant with ISO11898-2, ISO11898-5 and SAEJ2284 standards, with high electromagnetic compatibility (EMC) and electrostatic discharge (ESD) performance. When the supply voltage is turned off, the ATA6560/1 transceiver provides ideal passive performance for CAN bus, with a 3V to 5V supply voltage for direct connection to the MCU. For all kinds of high-speed CAN networks, especially CAN nodes that require low power consumption and need to wake up via the CAN bus, the ATA6560/1 with multiple operating modes and dedicated fail-safe functions is an excellent choice. The low-power CAN transceivers are developed on an advanced process, enabling further integration of analog functions and complex digital functions.
Qiu Jiayang, on-site application director of Microchip’s agent Shijian, said: Shijian, as a technology distributor and solution provider, always pays attention to the trend of market technology demand. By using Microchip’s high-performance Cortex-M0+ MCU, rich analog signals Link, power and interface products, combined with shunt sensors, Shijian provides customers with a complete shunt current detection solution, which can be widely used in automotive and energy storage BMS, electric and hybrid vehicles, industrial bus current detection and welding equipment and other high current detection applications.