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Magnetic Sensor ICs Offer Integrated Diagnostics for ASIL Compliance

由Gary Pepka，All亚博棋牌游戏egro Microsystems，LLC

Abstract

当前的智能车辆控制革命rol systems relies substantially on the rapidly developing physical detection technology called magnetic sensor integrated circuits (ICs). The complexity, reliability, flexibility, and functionality of these non-contacting, magnetic sensor ICs have all but dispelled the need for electromechanical switches in just about every application in latest generation automobiles. Yet, accompanying this increase in usage of complex electronic devices, is a heightened concern over difficult-todetect, system-level risks. This, in turn, has led the automotive industry to focus on automotive functional safety. The ISO 26262 functional safety standard outlines a development process including predictive analysis to minimize risk. This process, in turn, requires advanced diagnostics capabilities integrated directly into magnetic sensor IC systems. An examination is made of a new type of magnetic sensor IC that implements integrated diagnostics, using an innovative embedded solid state coil for end to end system test.

Overview

Open the door of any recent-model automobile and you are immediately surrounded by an invisible network of electronic sensors. They detect seat belt buckling, window or sunroof pinching, gear shifter position, engine transmission rotational speed and direction, and camshaft position, to name only a few applications. The penetration of real time sensing into these applications has been made practical by developments in various types of non-contacting magnetic detectors (i.e. Hall effect, Giant Magnetoresistive (GMR), Anisotropic resistive (AMR)). In addition to having very small form factors, these state-of-the-art, solid-state, semiconductor ICs are cost effective, power efficient, non-contacting, and gather a pervasive data stream in the harshest environment of vehicle engines with the subtlety to respond to the slightest of changes in vehicle conditions.

这些检测系统提供了高级的计算复杂程度，提供了高度的输出置换。这在实现功能安全性每ISO 26262时提出了挑战，因为设备状态复杂性和几乎无限各种车辆操作条件的组合使得所有使用场景和故障模式都不太可能通过设计或在测试程序中发现。鉴于可能需要几乎瞬时反应来保护乘客并保留车辆，这些巧妙的检测系统必须能够自我诊断，并且通常在运作不当时甚至纠正自己。

传统解决方案使用具有有限运营状态的机电开关（操作与否），因此故障检测是简单的。焊接簧片开关触点呈现短。破碎的开关弹簧防止输出状态变化。系统级别故障难以预测。预防性维护通常基于通用平均故障（MTTF）数据的时间（MTTF）数据，开关过度设计以在不调整的情况下容纳所有合理情况。

图1：基于磁场效果的传感器IC提供了紧凑的数据，包括换档地点，如换档机和安全带扣

图1：基于磁场效果的传感器IC提供了紧凑的数据，包括换档地点，如换档机和安全带扣

ICs can provide suboptimal outputs, so automotive use requires additional safety measures to avoid unreasonable residual risk according to Automotive Safety Integrity Levels (ASIL), ISO 26262. ASIL assigns safety goals, rather than characterizing entire systems or components. The rigorous ASIL level D requires manufacturers follow strict development guidelines, including Failure Modes Effects and Diagnostics Analysis (FMEDA) to quantify even very low risks of failures. These complexities require comprehensive diagnostics to ensure detection of system level failures and enable safe (limp home) modes.

安全关键应用中的冗余亚博尊贵会员

对于安全关键功能，系统中可行的选项是冗余。机电设计通常是笨重和在线，因此它们无法容纳失效冗余，其中可以在线带来替代控制。基于磁的控制系统通过允许自动交换控制电路到位，因为磁传感器IC不需要与检测到的机械目标或电路直接电连接。

Redundancy has many forms. A system can include a pair of non-contacting, magnetic sensor ICs in close proximity to each other. Each sensor IC has its own power, ground, and outputs, so if one fails, the other takes over after diagnostics detect a failure. A complementary sensor IC may be used simply to inform a controller that its cohort is not switching when it should. Moreover, there are sensor ICs capable of self-diagnosis, able to inform the controller when it is not operating properly, without the assistance of additional sensor ICs.

Enabled Diagnostics in Electronic Magnetic Sensor ICs

磁传感器IC可能需要监视，以确保设备本身正常运行，并且还要确保在相对于磁场的变化的适当时间发生切换。

One approach is to supply a single self-diagnosing sensor IC, which can be less costly, requires less PCB space, and is easier to manufacture in the application than two complementary sensor ICs. This solution also assists design engineers with meeting their targeted functional safety requirements, by addressing the complexity of determining proper electrical performance and magnetic switching.

A recent advancement in self-diagnostics, in particular with the phase involving applied magnetic field analysis, is the use of embedded detector coils on magnetic sensor IC chips. An example is shown in Figure 2, where Hall elements are surrounded by an embedded coil in theAllegro MicroSystems A1160 unipolar Hall-effect switch. This provides a cost effective and space saving solution, eliminating the need for external magnetic field conditioning structures to concentrate and guide the ambient magnetic field.

图2：磁场波动的检测

图2：磁场波动的检测

The detection of magnetic field fluctuations is enhanced by an innovative coil structure that surrounds the Hall elements in the Allegro MicroSystems A1160. The coil and Hall elements are embedded in the IC substrate.

该装置遵循典型的单极霍尔效应开关行为：当嵌入式霍尔元素感知嵌入式南极性磁场时，器件输出打开足够强度的垂直南极磁场以越过内部比较器开关点。该装置的独特方面是嵌入IC的硅中的片上线圈。线圈在霍尔元素周围缠绕。当逻辑I / O引脚被拉高时，该设备通过线圈通过10 mA的电流。通电线圈产生一个场，其由于线圈的近距离接近霍尔元件，足以打开设备并评估设备的整个信号路径（包括传感元件）。虽然诊断使能引脚很高，但设备输出脉冲宽度（PW）信号。如果PW信号具有50％的占空比，则设备被视为正常运行。如果PW信号具有0％或100％占空比，则设备被视为不正确的运行（参见图3）。

Figure 3: Self-diagnostics in the Allegro MicroSystems A1160

Figure 3: Self-diagnostics in the Allegro MicroSystems A1160

When the Diagnostic Enable pin is pulled high, the device outputs a diagnostic signal. A 50% duty cycle indicates proper operation.

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).

Figure 4: Matched Comparators

Figure 4: Matched Comparators

Matched comparators ensure self-diagnostics mode validates normal mode operation in the Allegro MicroSystems A1160.

为了防止偶然的外部转移的影响magnetic fields, this particular integrated coil concept provides the additional benefit of the coil being sensed differentially by the sensing elements. This means that the diagnostics function may be used at any time, even if the device is in the presence of an external magnetic field of sufficient strength to switch-on the device under normal operation mode. Additionally, as the sensing elements are reconfigured during diagnostics mode to be sensitive to the differential field, any external fields are rejected directly at the sensing elements.

Additional Applications Being Discovered

这种开创性的设备设计为响应ECU轮询信号提供模态诊断，并且开发设备也在启动时运行诊断。A1160的典型应用电路如图5所示，并且正在开发各种输出选项（2线或3线），具有定位，旅行，速度和方向变化的传感技术。最初为提高实现汽车市场的功能安全要求的能力，应用是无限的，包括工业自动化和白色商品。亚博尊贵会员

Figure 5: Typical Application Implementing a Magnetic Sensing IC Solution

Figure 5: Typical Application Implementing a Magnetic Sensing IC Solution.

Summary

用于提高可靠性和功能的汽车，工业和商业市场的不断发展的要求将继续推动对电子内容的需求，包括具有诊断的非接触磁传感器IC。创新的Allegro诊断开关与其集成线圈提供设计工程师，具有独特，经济高效和用户友好的解决方案，以满足几乎任何安全要求。

The information contained in this document does not constitute any representation, warranty, assurance, guaranty, or inducement by Allegro to the customer with respect to the subject matter of this document. The information being provided does not guarantee that a process based on this information will be reliable, or that Allegro has explored all of the possible failure modes. It is the customer’s responsibility to do sufficient qualification testing of the final product to insure that it is reliable and meets all design requirements.