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磁传感器IC为ASIL合规性提供集成诊断

By Gary Pepka, Allegro MicroSystems, LLC

抽象

智能车辆控制系统的当前革命基本上依赖于磁传感器集成电路（IC）的快速发展的物理检测技术。这些非接触式磁传感器IC的复杂性，可靠性，灵活性和功能，但在最新一代汽车中的每种应用中，所有磁力传感器IC都具有诸如对机电开关的需求。然而，随着这种复杂电子设备的使用增加，对难以陷入困难，系统级风险的增加是一种高度的兴趣。反过来，这导致了汽车行业专注于汽车功能安全。ISO 26262功能安全标准概述了一种开发过程，包括预测分析，以尽量减少风险。反过来，这一过程需要直接集成到磁传感器IC系统中的高级诊断功能。检查采用新型磁传感器IC，实现集成诊断，采用创新的嵌入式固态线圈，以结束终端系统测试。

概要

打开任何最近模型汽车的门，您立即被一个不可见的电子传感器网络包围。它们检测座椅带弯曲，窗户或天窗夹紧，换档器位置，发动机传输转速和方向，以及凸轮轴位置，只有几种应用。亚博尊贵会员通过各种类型的非接触磁力检测器的开发（即霍尔效应，巨磁阻（GMR），各向异性电阻（AMR））进行亚博尊贵会员了实际时间对这些应用的渗透。除了具有非常小的形状因素外，这些最先进的，固态，半导体IC是具有成本效益，功率高，不接触的，并在车辆发动机的最严苛环境中收集普遍存在的数据流微妙的响应车辆条件的最轻微的变化。

These detection systems provide an advanced level of computing sophistication, providing a high degree of output permutations. This has presented a challenge in achieving functional safety per ISO 26262, because the combination of device state complexity and the almost infinite variety of vehicle operating conditions makes it unlikely that all usage scenarios and failure modes can be anticipated by design or discovered in testing programs. Given that almost instantaneous response may be required to protect passengers and preserve the vehicle, these ingenious detection systems must be able to self-diagnose, and often even correct themselves, when they are functioning improperly.

Traditional solutions use electromechanical switches with limited operational states (operating or not), so failure detection is straightforward. Welded reed switch contacts present a short. Broken switch springs prevent output state change. System level failures are difficult to anticipate. Preventive maintenance is often based on generic Mean Time to Failure (MTTF) data, with switches over-designed to accommodate all reasonable circumstances without adjustment.

Figure 1: Magnetic Hall-effect Based Sensor ICs Provide Compact Data Gathering in Restricted Locations Such as Gear Shifters and Seat Belt Buckles

Figure 1: Magnetic Hall-effect Based Sensor ICs Provide Compact Data Gathering in Restricted Locations Such as Gear Shifters and Seat Belt Buckles

IC可以提供次优输出，因此汽车用途需要额外的安全措施，以避免根据汽车安全完整性（ASIL），ISO 26262。ASIL分配安全目标，而不是表征整个系统或组件。严格的ASIL级别D要求制造商遵循严格的发展指南，包括失败模式效果和诊断分析（FMEDA）来量化甚至非常低的故障风险。这些复杂性需要全面的诊断，以确保检测系统级故障并启用安全（LIMP HOME）模式。

Redundancy in Safety Critical Applications

For safety critical functions, a feasible option is redundancy in the system. Electromechanical designs are typically bulky and in-line, so they cannot accommodate fail-over redundancy, where alternative controls can be brought on line. Magnetics-based control systems accommodate fail-over redundancy by allowing automatic swapping of control circuits in place, because magnetic sensor ICs do not require contact or direct electrical connection with the mechanical target or electrical circuit being detected.

冗余有多种形式。系统可以包括一对非接触的磁传感器IC，彼此靠近邻近。每个传感器IC都有自己的电源，接地和输出，因此如果失败，则另一个在诊断检测到失败后接管。可以使用互补的传感器IC来通知控制器，即它的队列当它应该时不会切换。此外，有能够自诊断的传感器IC，能够在没有额外的传感器IC的帮助下运行时通知控制器。

在电子磁传感器IC中启用诊断

Magnetic sensor ICs may require monitoring to ensure that the device itself is operating properly and also to ensure switching occurs at the appropriate time with respect to a change in magnetic field.

一种方法是提供一种自诊断的传感器IC，其可以更昂贵，需要较少的PCB空间，并且在应用于两个互补传感器IC时更容易制造。该解决方案还通过解决确定适当的电气性能和磁性开关的复杂性，帮助设计工程师满足其目标功能安全要求。

最近自我诊断的进步，特别是涉及应用磁场分析的阶段，是在磁传感器IC芯片上使用嵌入式检测器线圈。图2中示出了一个例子，其中霍尔元素被嵌入式线圈包围在内亚博棋牌游戏Allegro Microsystems A1160 UniPolar Hall效果开关。这提供了一种成本效益和节省空间的解决方案，消除了外部磁场调节结构的需要集中和引导环境磁场。

Figure 2: Detection of Magnetic Field Fluctuations

Figure 2: Detection of Magnetic Field Fluctuations

通过创新的线圈结构增强了磁场波动的检测，该模型线圈结构围绕Allegro Microsystems A1160中的霍尔元素。亚博棋牌游戏线圈和霍尔元件嵌入IC基板中。

The device follows the typical unipolar Hall-effect switch behavior: the device output turns on when the embedded Hall elements sense a perpendicular south polarity magnetic field of sufficient strength to cross the internal comparator switch point. The unique aspect of the device is the on-chip coil embedded in the silicon of the IC. The coil wraps around the Hall elements. When a logic I/O pin, called the Diagnostic Enable pin, is pulled high, the device passes 10 mA of current through the coil. The energized coil generates a field, which, due the close proximity of the coil to the Hall elements, is sufficient to turn on the device and evaluate the entire signal path of the device (including the sensing elements). While the Diagnostic Enable pin is high, the device outputs a pulse width (PW) signal. If the PW signal has a 50% duty cycle, the device is deemed functioning properly. If the PW signal has a 0% or a 100% duty cycle, then the device is deemed functioning improperly (see Figure 3).

图3：Allegro Microsystems中的自诊断A1160亚博棋牌游戏

图3：Allegro Microsystems中的自诊断A1160亚博棋牌游戏

当诊断使能引脚拉高时，设备输出诊断信号。50％的占空比表明正常运行。

To enable self-calibration for these diagnostics, the number of coil turns is fixed and the amount of current is regulated .Therefore, the amount of field generated by the coil is precisely repeatable and if the diagnostic magnetic field changes for some reason (i.e. due to time or stress), the diagnostic mode can detect it. The comparator is the same for both diagnostic mode and normal operation, and what changes is the offset (mV) between diagnostic mode and normal operation (see Figure 4). As a result, when the device is in diagnostics mode, the operation of the diagnostics signal from the regulator to the energized coil and all the way to the output provides an end-to-end test of the full signal path (see Figure 4).

图4：匹配的比较器

图4：匹配的比较器

匹配的比较器确保自诊断模式验证Allegro Microsystems A1160中的正常模式操作。亚博棋牌游戏

为了防止移位外部磁场的偶然效果，这种特定的集成线圈概念通过感测元件提供了差异感测的线圈的额外益处。这意味着即使该设备在正常操作模式下，即使设备在存在足够强度的外部磁场的外部磁场存在下，也可以使用诊断功能。另外，由于在诊断模式期间重新配置感测元件，以对差分敏感，因此任何外部字段都被直接拒绝在感测元件处。

正在发现其他应用程序亚博尊贵会员

This pioneering device design provides modal diagnostics in response to an ECU polling signal, and devices in development also run diagnostics at startup. A typical application circuit for the A1160 is shown in Figure 5, and a variety of output options (2-wire or 3-wire) are being developed, with sensing technologies for position, travel, speed, and direction change. Initially for enhancing the ability to achieve functional safety requirements for the automotive market, applications are limitless, including industrial automation and white goods.

图5：实现磁感测IC解决方案的典型应用

图5：实现磁感测IC解决方案的典型应用。

概要

The ever-evolving requirements of the automotive, industrial, and commercial markets for increased reliability and functionality will continue to drive demand for electronic content, including non-contact magnetic sensor ICs with diagnostics. The innovative Allegro diagnostic switch with its integrated coil provides design engineers with a unique, cost-effective and user-friendly solution to satisfy almost any safety requirement.

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