Low-cost and high-precision shunt detection scheme based on Microchip

BMS (Battery Management System) is a bridge that connects the battery, the core component of new energy vehicles, and the entire vehicle. Benefiting from the development of new energy vehicles, BMS as a core component has also been 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 detection is essential. The current detection of BMS is divided into traditional Hall sensor detection method and shunt detection method.

The shunt detection method has become the first choice, on the one hand because of its high measurement accuracy and relatively low cost, on the other hand because of its simple measurement method, less equipment, convenient and fast. The measurement principle is to directly measure the voltage across the shunt. According to Ohm’s law, the current value in the circuit can be obtained by dividing the measured voltage by the resistance of the shunt. Although the Hall sensor detection method has a simple structure, its measured value changes 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.

This solution uses Bourns’ high-current shunt CSM2F-8518-L100J32, Microchip’s MCU SAMC21E18A, 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 ΔΣADC MCP3421 converts the amplified analog signal into a digital signal, and transmits it to the Microchip MCU SAMC21E18A through the I2C interface, and then the MCU performs data processing. For reading, processing and calibration, Microchip’s CAN interface ATA6560 is used for data communication. In addition to the BMS system, this solution can also be used for electric and hybrid vehicles, bus current detection and welding equipment.

Low-cost and high-precision shunt detection scheme based on Microchip

The characteristics of the shunt scheme: 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 has a wide range of voltage input, the current consumption is less than 3mA at 12V, the operating temperature range is -40~125 ℃, the continuous detection current is 500A, and the maximum impulse current is 1000A (30mins on/off)

In order to facilitate the user’s testing, calibration and application, the program also provides host computer software. Through the bridging tool, users can intuitively calibrate and test the shunt solution. The MCU’s built-in Flash supports read and write functions, which are used to simulate the EEPROM function to store the calibrated data. The NTC temperature sensor is attached to the board and the shunt, and the user can read the temperature on the board and the shunt in real time.

Low-cost and high-precision shunt detection scheme based on Microchip

After understanding the overall characteristics of this current detection scheme, let’s introduce the respective characteristics of the core devices that make up this scheme one by one.

Start with the MCU of this solution. Microchip MCU SAMC21E18A features a 32-bit Cortex M0+ MCU, which can be powered by 5V, and the flexible serial peripheral Sercom can be flexibly configured as UART, SPI and I2C; the built-in CAN controller supports CAN-FD, Compatible with CAN2.0 A/B at the same time.

Its amplifier MCP6N16 has a self-correcting architecture, which can maximize DC performance through ultra-low offset, low offset drift, and excellent common mode and power supply suppression functions, while eliminating the adverse effects of 1/f noise, thereby achieving full temperature range Super high precision. MCP6N16’s low-power CMOS process technology can provide 500 kHz bandwidth while achieving low power consumption. In addition, it is equipped with a hardware enable pin to further reduce power consumption. For a given speed and performance, this low-power operation and shutdown function requires less current, which can extend battery life and reduce self-heating. The operating voltage of the amplifier is as low as 1.8V, which makes the power consumption of two 1.5V dry batteries much less than in the typical case, and its rail-to-rail input and output operation can ensure full range use even under low power supply conditions . This makes the performance within the entire operating voltage range greatly improved. The MCP6N16 instrumentation amplifier is very suitable for applications that require high performance, high accuracy, low power consumption, and low voltage operation. It covers sensor interfaces, signal conditioning, fixed and portable instruments in the medical, consumer and industrial markets.

Compared with other A/D converters, MCP3421 is especially suitable for various high-precision A/D conversion applications that require simple design, low power consumption and space saving. Its characteristics are mainly manifested in: fully differential input, 18-bit resolution, precise continuous self-calibration function; can choose 3.75, 15, 60 or 240SPS sampling rate for conversion; can work in continuous conversion or single conversion mode, in single It automatically enters the standby mode during the idle period after the conversion, which greatly reduces the current consumption; the internal integration of 2.048V 0.05% accuracy, and the temperature drift is only 5ppm/℃ reference voltage source, the programmable gain amplifier (PGA) provides 1/ 2/4/8 times the gain, allows the measurement of very small signals and has a high resolution, the internal integrated oscillator circuit and provide I2C serial interface, etc.

Bryan J. Liddiard, vice president of Microchip’s Hybrid and Linear Signal Products Division, said: “The development of the ADC market and applications requires higher resolution, higher speed, and higher accuracy. In addition, lower power consumption and smaller packages are also very important. Importantly, our newly launched products can meet all of the above needs.”

The high-voltage input integrated switching buck regulator MCP16331 can work with an input voltage source up to 50V. Integrated features include high-side switch, 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 a minimum of external components. High converter efficiency is achieved by integrating current-limiting components, low resistance, high-speed N-channel MOSFETs and related drive circuits. The high switching frequency minimizes the size of the external filter components, thereby realizing a small size solution. 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, which can stabilize the output voltage even during input voltage steps and output current transient conditions that are common in power supply systems. The EN input is used to turn the device on and off. For power limiting and load sharing applications, when the device is turned off, the input only consumes a few μA of current. This pin is internally pulled up, so even if the EN pin is left floating, the device will still start. The output voltage can be set by an external resistor divider.

The automotive and industrial CAN markets have been demanding cost-effective solutions that provide higher performance, lower power consumption, and greater flexibility. Microchip’s new series of high-speed CAN transceivers meet high-performance requirements, provide industry’s low standby current, and have a variety of compact devices to choose from. Microchip’s ATA6560/1 transceiver supports the CAN FD standard and a data rate of up to 5Mbits/s, and provides a docking interface for the CAN protocol controller and the CAN two-wire physical bus. It complies with ISO11898-2, ISO11898-5 and SAEJ2284 standards, and has high electromagnetic compatibility (EMC) and electrostatic discharge (ESD) performance. When the power supply voltage is off, the ATA6560/1 transceiver can provide ideal passive performance for the CAN bus, and is equipped with a MCU direct connection port with a power supply voltage of 3V to 5V. For all kinds of high-speed CAN networks, especially CAN nodes that require low power consumption and need to be awakened via the CAN bus, the ATA6560/1 with multiple operating modes and dedicated fail-safe functions is undoubtedly an excellent choice. Low-power CAN transceivers are developed based on advanced technology and can further integrate analog functions and complex digital functions.

Shijian Company’s Field Application Director Qiu Jiayang said: Shijian Company, as a technology distributor and solution provider, always pays attention to market technology demand dynamics. By adopting Microchip’s high-performance Cortex-M0+ MCU, rich analog signal chain, power supply and Interface products, combined with shunt sensors, Shijian provides customers with complete shunt current detection solutions, which can be widely used in automobiles and energy storage BMS, electric and hybrid vehicles, industrial bus current detection and welding equipment, etc. Application of high current detection.

The Links:   1MBI300NN-120 LM171WX3-TLC2

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