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　　LTC6802 detection circuit design of series battery pack voltage

　　1. Introduction to LTC68022

　　The LTC68022 contains a 12-bit AD converter, precision voltage reference, high-voltage input multiplexer and SpI serial interface. Each chip can detect 12 batteries connected in series. At the same time, the chip also supports series use. Up to 16 chips can be used in series, that is, a battery pack composed of up to 12x16=192 cells connected in series can be detected. The conversion range of each AD is 0~5V, so each chip can detect the voltage of the series connected battery pack up to 60V. In addition, LTC6802.2 has been improved on the basis of LTC68021, adding a 4-bit external addressing interface A0~A3, which can be addressed, which facilitates the independent operation of a specified detection unit. In addition, LTC6802.2 also has high-temperature protection functions, battery overcharge and over-discharge status monitoring, and power balancing functions.

　　LTC6802.2 has three working modes: standby mode, measurement mode and supervisor mode. The power-on default is standby mode. In this mode, only the serial port and the 5V regulated reference source are in working state, and all other circuits are inactive. The LTC6802.2 must be configured through serial ISI communication before other circuits can be started. At this time, a non-0 value can be written to the CDC[2:0] bits of CFGR0 to exit the standby mode. After the LTC68022 exits the standby mode, the VREF pin The pin can detect the pulse reference voltage signal of 3.075V, otherwise the detection voltage is 0V, which can be used as a detection basis to judge the success of serial communication.

　　2. Hardware design

　　This article mainly uses 51 microcontroller and TMS320LF2407 as the main controller, introduces their hardware interface circuits respectively, and analyzes the problems encountered during the debugging process.

　　2. Communication interface between 151 microcontroller and LTC68022

　　Figure 1 shows the control circuit with 51 microcontroller as the controller. Under the normal working conditions of the circuit, the peripheral circuit is given in the simplest form. If a large-capacity power battery is used as the battery, a clamp protection circuit should be considered to prevent large current from the C pin from damaging the chip. Because the communication interfaces of the 51 microcontroller and LTC6802.2 both have a 5V working voltage, when only one LTC6802.2 is connected, serial communication can be performed directly without adding an isolation device.

　　The SpI serial communication interface of the 51 microcontroller uses p1. O~p1.3 is used to simulate. When simulating the SpI interface, please note that the interface does not have other expansion purposes. If there are other expansion circuits, it must be shielded during SpI communication, otherwise it may cause interference to the serial communication. , causing normal communication to fail.

　　2.2 Communication interface between TM$320LF2407 and LTC68022

　　TI's TMS320LF2407 has its own SpI serial communication module. This module can be used to simply implement communication between DSp and LTC68022. It should be noted in communication that the general SpI module generally gives the corresponding chip select signal to the CS pin every time a read or write operation is performed. However, according to the timing requirements of LTC6802.2, every time the chip select is valid, it must be Multiple read and write operations. Therefore, the chip select of the SpI module cannot be used here. In the experiment, pB4 of DSp was selected to give the chip select signal.

　　Another point that needs to be noted in the design is the selection of digital isolation devices. Because the driving capability of the 5V reference power supply of the LTC68022 is relatively weak and can only provide a maximum load current of 4mA, you must choose a low-power device when selecting a digital isolation device. Otherwise, excessive power consumption will cause the LTC68022 chip to heat up and the reference power supply voltage to drop. When it drops to 4.1V, the chip will not work properly. This article selects ADUM14115_, which is an ultra-low power consumption 4-channel digital isolation chip developed by ADI. It combines the needs of SpI communication here and has low power consumption. The maximum communication speed can reach 10M, which also meets the communication needs. Figure 2 is the working circuit of TMs320LF2407 and LTC6802.2.

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