Vehicle Tracking System: Under Control Anytime, Anywhere

车辆跟踪系统非常适合监视一辆汽车或整个车队。跟踪系统由自动跟踪硬件和用于收集数据(如果需要的话，还有数据传输)的软件组成。2015年，全球车队管理市场的规模为80亿美元，预计到2022年将超过220亿美元，从2016年到2023年，年复合增长率将超过20%(数据来源：Global Market Insights)。拉美、中东和非洲对商用车辆的需求在上升，这对车辆跟踪系统而言也是一种潜在的增长机会。在欧洲、北美等发达地区，预计物联网(IoT)技术与车辆的集成会促使车辆跟踪系统采用率的提高，尽管集成的高成本减缓了这一过程。此外，预计同一时期亚洲车辆跟踪市场的规模将显著增长，日本、印度和中国是起主要驱动作用的国家。这些新兴市场之所以潜力巨大，主要是因为商用车辆众多。同一时期，在拉美、中东和非洲，由于不同国家车辆采用率的上升，车辆跟踪市场预计也会有适度增长(数据来源：Global Market Insights)。

　　1 Active Tracker vs Passive Tracker

　　Active and passive trackers collect data in the same way and are equally accurate. The main difference between the two types of trackers is time. Active trackers are also called "real-time" trackers because they send data via satellite or cellular networks, indicating the vehicle's location in real time. A computer screen can show the vehicle's movement in real time. Therefore, if a company wants to improve delivery efficiency and understand the driving situation of employees in the field, active tracking is the best choice. Active trackers also have a "geofencing" capability (think of this function as a "force field"), which can provide an alert signal when the car enters or leaves a predetermined location (Source: RMT). In addition, this type of system can help prevent vehicle theft or recover stolen vehicles. Of course, active GPS tracking devices are more expensive than passive tracking devices and require a monthly service fee.

　　Passive trackers, on the other hand, are less expensive but have limited data storage, though they are smaller and easier to hide. Passive trackers store information on the device rather than sending it to a remote location. The device must be removed from the vehicle and connected to a computer in order to view the information stored on it. This type of system is suitable for people who track mileage for work purposes, as well as for businesses that want to reduce vehicle abuse. Passive trackers are also often used to monitor the movements of people (think of it as detective work). If you don't need immediate feedback, but want to check the device data regularly, then a passive tracker is a good choice.

　　Regardless of the type of tracker, they are inherently portable and relatively small in size. Therefore, battery power is required, as well as backup capabilities to preserve data in the event of a power outage. Due to the higher automotive system voltages and higher currents required to charge the battery (usually a single-cell Li-ion battery), a switch-mode charger is desirable because it charges more efficiently and generates less heat in the form of power dissipation than a linear battery charging IC. In general, the input voltage for embedded automotive applications can be as high as 30 V, and some are even higher. In these GPS tracking and positioning systems, a charger and the common 12 V to single-cell Li-ion battery (typically 3.7 V), additional protection for much higher input voltages (in the event of voltage transients from battery drift), and some type of backup capability would be ideal.

　　2 Design Issues of Battery Charging IC

　　Traditional linear topology battery chargers are often valued for their compact footprint, simplicity, and moderate cost. However, traditional linear chargers have some disadvantages, including limited input and battery voltage ranges, relatively high current consumption, excessive power dissipation (heat generation), limited charge termination algorithms, and relatively low efficiency. On the other hand, switch-mode battery chargers are a popular choice because of their topology flexibility, ability to charge a variety of battery chemistries, high charging efficiency to minimize heat, fast charging, and wide operating voltage range. Of course, there are always trade-offs. The disadvantages of switching chargers include relatively high cost, more complex inductor-based designs, potential noise generation, and a large solution footprint. Due to the advantages of switching chargers mentioned above, modern lead-acid batteries, wireless power, energy harvesting, solar charging, remote sensors, and embedded automotive applications are mostly powered by switch-mode chargers.

　　Traditionally, the backup power management system for batteries in trackers consists of multiple ICs, including a high-voltage buck regulator and a battery charger, as well as all discrete components, which is by no means a compact solution. As a result, the form factor of early tracking systems was not very compact. Typical tracking system applications use automotive batteries and single-cell lithium-ion batteries to support storage and backup.

　　So why do tracking systems require more integrated power management solutions? First, the size of the tracker itself must be reduced; in this market, smaller is better. There are also requirements to safely charge the battery and protect the IC from voltage transients, have system backup capabilities in case the system power disappears or fails, and power the relatively low rail voltage (~4.45 V) of the General Packet Radio Service (GPRS) chipset.

　　3Power Backup Manager

　　A solution that integrates a power backup manager and charger to meet the aforementioned requirements needs to have the following features:

　　Synchronous buck topology for high efficiency;

　　Wide input voltage range to accommodate a wide range of input supplies and provide protection against high voltage transients;

　　· Appropriate battery charging voltage to support GPRS chipset;

　　Simple and autonomous operation with built-in charge termination (no microprocessor required);

　　PowerPath™ control – provides seamless switching between input power and backup power in the event of a power failure, and also provides reverse isolation in the event of an input short circuit;

　　Provides battery backup to power system loads when input disappears or fails;

　　Due to space constraints, a flat solution with a small footprint is required;

　　Advanced packaging to improve thermal performance and space utilization.

　　To meet these specific needs, Analog Devices recently introduced the LTC4091, a complete lithium-ion battery backup management system for 3.45 V to 4.45 V rails that must remain operational during extended main power failures. The LTC4091 uses a 36 V monolithic step-down converter with adaptive output control to power the system load from the step-down converter output and support high-efficiency battery charging. When external power is available, the device can provide up to 2.5 A of total output current and can provide up to 1.5 A of charging current for a single 4.1 V or 4.2 V lithium-ion battery. If the main input source fails and can no longer power the load, the LTC4091 provides up to 4 A of current from the backup lithium-ion battery to the system output load through an internal ideal diode, or relatively unlimited current if an external ideal diode transistor is used. To protect sensitive downstream loads, the maximum output load voltage is limited to 4.45 V. The device's PowerPath™ control provides seamless switchover between input and backup supplies during a power failure, supporting reverse isolation with shorted inputs. Typical applications for the LTC4091 include fleet and asset tracking, automotive GPS data loggers and telematics systems, security systems, and communications and industrial backup systems.

　　The LTC4091 provides 60V absolute maximum input overvoltage protection, so the IC can withstand very high input voltage transients. The LTC4091's battery charger provides two pin-selectable charging voltages optimized for lithium-ion battery backup applications: a standard 4.2 V voltage and a 4.1 V selectable voltage that trades off battery run time and charge/discharge cycle life. Other features include soft-start and frequency foldback to control output current during startup and overload, as well as trickle charging, automatic charging, low battery precharge, charge timer termination, thermal regulation, and a thermistor pin for temperature-qualified charging.

　　The LTC4091 is available in a low profile (0.75 mm) 22-lead 3 mm x 6 mm DFN package with a backside metal pad for excellent thermal performance. The device operates over the –40 °C to 125 °C temperature range. Figure 1 shows a typical application schematic for the device.

　　Figure 1 Typical application schematic diagram of LTC4091

　　AUTOMOTIVE INPUT: Auto input

　　6V TO 36V：6V 至 36V

　　2A MAX: 2A maximum value

　　LOAD: Load

　　4.45V MAX: 4.45V maximum value

　　Li-Ion BATTERY: Lithium-ion battery

　　4Heat regulation protection

　　To prevent excessive heat from damaging the IC or surrounding components, an internal thermal feedback loop automatically reduces the set charge current if the die temperature rises to approximately 105 °C. Thermal regulation prevents the LTC4091 from overheating due to high power operation or high ambient temperature, allowing the user to push the limits of the power handling capabilities of a given board design without risking damage to the LTC4091 or external components. The benefit of the thermal regulation loop is that the charge current can be set according to actual conditions rather than worst-case conditions, while ensuring that the battery charger automatically reduces the current under worst-case conditions.

　　5. Cold start of the car

　　Automotive applications experience large drops in supply voltage, such as during a cold crank condition, which can cause the high voltage switching regulator to lose regulation, resulting in excessive VC voltage and, therefore, excessive output overshoot when VIN recovers. To prevent overshoot when recovering from a cold crank condition, it is necessary to reset the LTC4091’s soft-start circuitry via the RUN/SS pin. Figure 2 below shows an example of a simple circuit that automatically detects an undervoltage condition and resets the RUN/SS pin, reengaging the soft-start function and preventing destructive output overshoot.

　　Figure 2 Cold start ride-through circuit

　　AUTOMOTIVE INPUT: Auto input

　　6 Conclusion

　　The adoption of vehicle and fleet tracking systems is increasing. Modern trackers are decreasing in size and increasing in functionality, including active data transmission to support real-time tracking. In addition, backup capabilities are required as well as lower voltages to power the GPRS chipset in the system. ADI's Power by Linear™ product, the LTC4091, is a high voltage, high current step-down battery charger and PowerPath backup manager with thermal regulation and extensive protection, making the designer's task simpler and easier by providing a compact, powerful and flexible single-chip solution for vehicle tracking applications.