過去十年，隨著新技術(shù)的演進(jìn)，汽車電子設(shè)備的安全性和可靠性標(biāo)準(zhǔn)也有了很大改變。許多以前消費(fèi)者購買汽車時(shí)作為選配的技術(shù)，包括穩(wěn)定性控制和防抱死制動(dòng)系統(tǒng)等，現(xiàn)在都已經(jīng)是大多數(shù)車輛的標(biāo)配。而車道偏離警告系統(tǒng)，車輛通信系統(tǒng)和夜視鏡等新型電子設(shè)備則成為可選配的新款電子設(shè)備。
隨著汽車設(shè)計(jì)與制造各方面的要求不斷提升，設(shè)計(jì)師們必須充分了解汽車認(rèn)證標(biāo)準(zhǔn)方面的要求，而且這些要求比消費(fèi)者電子產(chǎn)品的保護(hù)要求涵蓋范圍更廣。但是，在設(shè)計(jì)要能夠符合標(biāo)準(zhǔn)則面臨了諸多技術(shù)挑戰(zhàn)。
雖然集成電路因其體積更小，速度更快在汽車中被使用，但卻更容易遭受靜電放電（ESD）的損害。在認(rèn)證測(cè)試過程中通過仿真實(shí)驗(yàn)，我們有針對(duì)的模擬電氣瞬變的車真實(shí)場(chǎng)景，來測(cè)試這些設(shè)備是否達(dá)標(biāo)。
本文旨在提供汽車標(biāo)準(zhǔn)和電路的實(shí)際應(yīng)用和解決方案，目的是幫助電路設(shè)計(jì)師們實(shí)現(xiàn)穩(wěn)健、可靠的設(shè)計(jì)。首先，本文會(huì)強(qiáng)調(diào)兩種測(cè)試標(biāo)準(zhǔn)的測(cè)試要求，并探討需要保護(hù)的汽車電路的最常見類型。然后，本文會(huì)解釋先進(jìn)的電路保護(hù)技術(shù)，用于保護(hù)多種汽車應(yīng)用，并且這些技術(shù)應(yīng)納入早期設(shè)計(jì)階段，以確保安全性和可靠性。
符合汽車測(cè)試標(biāo)準(zhǔn)
為了保證先進(jìn)的車輛電子設(shè)備可以合格上市，電路設(shè)計(jì)師們必須充分了解ISO 10605和AEC-Q101的測(cè)試標(biāo)準(zhǔn)要求。
ISO 10605: 該國際標(biāo)準(zhǔn)詳細(xì)說明了為公路用車研發(fā)的電子模塊評(píng)估的ESD測(cè)試方法。所有模塊必須能夠抵抗由裝配，保養(yǎng)/維修，和操作引起的電干擾。對(duì)于ISO10605合規(guī)來說，每個(gè)電路和模塊必須在裝配到車內(nèi)之前進(jìn)行預(yù)先測(cè)試。汽車裝配完畢后，也必須經(jīng)過測(cè)試，以確保安全性和可靠性。
AEC-Q101: ISO 10605著重于電氣危害，而AEC-Q101則關(guān)于環(huán)境的具體要求。該標(biāo)準(zhǔn)詳述了一系列合格性測(cè)試，目的是確保基于半導(dǎo)體的汽車部件的長(zhǎng)期可靠性。ESD保護(hù)裝置，諸如瞬態(tài)電壓抑制（TVS）二極管，以及TVS二極管陣列，必須符合AEC-Q101標(biāo)準(zhǔn)，這樣汽車制造商才能將它們裝配到車內(nèi)。AEC-Q101的合規(guī)部件必須能經(jīng)受熱沖擊和熱循環(huán)，極端溫度，以及高濕度環(huán)境。
明確需要保護(hù)的汽車電路
所有電路和部件都容易遭受電磁瞬變的損害——這一點(diǎn)與它們?cè)谲囕v內(nèi)部的裝配位置無關(guān)。以下列舉了四個(gè)最常見的需要保護(hù)的電路：
1. 老式雙路通信公交車：
a. 控制器局域網(wǎng)絡(luò)（CAN）：該標(biāo)準(zhǔn)允許微控制器和裝置實(shí)現(xiàn)車內(nèi)通信，而無需使用主機(jī)。CAN系統(tǒng)具有多種功能——從動(dòng)力轉(zhuǎn)向到發(fā)動(dòng)機(jī)計(jì)算機(jī)和變速器之間的重要的傳動(dòng)系統(tǒng)通信。
b. 局域互聯(lián)網(wǎng)絡(luò)（LIN）：該串行網(wǎng)絡(luò)協(xié)議用于車內(nèi)部件間的通信。LIN公交車具有簡(jiǎn)單的電機(jī)功能，諸如移動(dòng)電動(dòng)座椅，以及開關(guān)恒速操縱器。
CAN/LIN公交車有更高的瞬時(shí)突波發(fā)生概率，可能會(huì)造成未受保護(hù)的CAN/LIN無線電收發(fā)機(jī)故障。圖2刻畫了CAN和LIN公交車保護(hù)的實(shí)用策略。
2. 高速數(shù)字公交車：USB/HDMI接口支持的車內(nèi)消費(fèi)者應(yīng)用。例如，儀表板或許會(huì)有一個(gè)USB接口，乘客可以用它為手機(jī)/平板電腦充電或者播放音樂。HDMI接口是備用接口，也可用于連接車內(nèi)前視攝像頭。這些接口的數(shù)據(jù)流量越來越快，芯片敏感性越來越高，因此需要卓越的信號(hào)完整性和系統(tǒng)可靠性。USB/HDMI接口可能會(huì)因車內(nèi)的相對(duì)小型ESD事件和短路而遭到損壞。
3. Wi-Fi通信/SIM卡槽：該技術(shù)允許車輛為乘客提供蜂窩3G或LTE通信。SIM模塊是電路的中介部分，能將LTE轉(zhuǎn)換成Wi-Fi，用戶可以連接手機(jī)、平板電腦和筆記本電腦。SIM卡槽需要ESD保護(hù)，因?yàn)樵谀K裝載或替換到車內(nèi)時(shí)，卡槽易受人類活動(dòng)的影響。
4. 高頻通信/RF（無線射頻）：該技術(shù)由短程RF電路支持，可以實(shí)現(xiàn)車對(duì)車或車對(duì)路通信。網(wǎng)絡(luò)可以讓車輛發(fā)現(xiàn)彼此，并實(shí)現(xiàn)相互通信，有助于防止碰撞事故的發(fā)生，也有利于建設(shè)智能交通系統(tǒng)。RF放大器的前端對(duì)ESD非常敏感。無偏差RF信號(hào)能夠在天線電路上產(chǎn)生正負(fù)極性電壓。
匹配電路保護(hù)方案和汽車應(yīng)用
汽車電路設(shè)計(jì)師們或許很難獲得高質(zhì)量的電路保護(hù)方案，因?yàn)橛心芰ρ邪l(fā)滿足AEC-Q101標(biāo)準(zhǔn)的產(chǎn)品的公司屈指可數(shù)。在選擇汽車制造商時(shí)，務(wù)必要驗(yàn)證該制造商的資質(zhì)證書，以確保該公司的產(chǎn)品滿足所有產(chǎn)業(yè)適用標(biāo)準(zhǔn)。該公司也應(yīng)該遵守產(chǎn)品設(shè)計(jì)的最佳實(shí)踐，并應(yīng)用高質(zhì)量制造工藝。表1列出了一些電路保護(hù)方案，都應(yīng)在早期設(shè)計(jì)階段實(shí)施。
結(jié)論
穩(wěn)健的汽車電子設(shè)備設(shè)計(jì)要求提前規(guī)劃環(huán)境和電氣危害管理。成功的設(shè)計(jì)始于對(duì)ISO 10605和AEC-Q101測(cè)試標(biāo)準(zhǔn)要求的充分理解。每一個(gè)應(yīng)用層的電子設(shè)備都需要充分的保護(hù)，因?yàn)檎嚰捌渲械拿恳粋€(gè)模塊都會(huì)經(jīng)過全面的可靠性測(cè)試。
電路設(shè)計(jì)師也應(yīng)該考量需要保護(hù)的汽車電路的電氣脆弱性，尤其是與新型通信和網(wǎng)絡(luò)相關(guān)的電路。通過了解汽車測(cè)試的標(biāo)準(zhǔn)和電路，設(shè)計(jì)師們就能夠選擇可以為其所用的最佳電路保護(hù)方案。
本文由來自Littelfuse有限公司James Colby為《汽車工程雜志》撰稿。
作者：James Colby
來源：SAE《汽車工程雜志》
翻譯：SAE上海辦公室
Understanding the Importance of electrostatic discharge standards
Within the past decade, the safety and reliability standards for automotive electronics have changed significantly as new technologies have evolved. Technologies that used to be sold as options, including stability control and antilock brakes, are now offered as standard features in most vehicles. Today’s innovative automotive electronics enable lane-departure warning, vehicle communications, and night vision.
This shift in design and manufacturing mandates that designers understand the demands of the automotive certification standard that extends beyond the protection requirements for consumer electronics. However, designing for the automotive standard involves several technology challenges.
As automotive integrated circuits continue getting smaller and faster, they become more susceptible to damage from electrostatic discharge (ESD). In addition, the automotive environment is marked by harsh electrical transients, which are simulated during automotive certification testing.
This article makes practical application of automotive standards, circuits, and solutions to help circuit designers create robust, reliable designs. First, it highlights the testing requirements of two test standards and discusses the most common types of automotive circuits requiring protection. Then, it identifies advanced circuit protection technologies for several automotive applications that should be implemented early in the design phase to ensure safety and reliability.
Measuring up to automotive test standards
Circuit designers must consider the requirements of the ISO 10605 and AEC-Q101 test standards for their advanced vehicle electronics to be qualified for the automotive market.
ISO 10605: This international standard specifies ESD test methods for evaluating electronic modules developed for use in road vehicles. The modules must be able to manage electrical disturbances caused by assembly, maintenance/repair, and operation. For ISO 10605 compliance, every circuit and module must be pretested before being added to the vehicle. Once the assembled car is ready, it must also be tested to ensure safety and reliability.
AEC-Q101: While ISO 10605 focuses on electrical hazards, AEC-Q101 is an environmental specification. It describes a series of qualification tests that ensure the long-term reliability of semiconductor-based components in the automobile. ESD protection devices such as transient voltage suppression (TVS) diodes and TVS diode arrays must increasingly conform to the AEC-Q101 standard for a vehicle manufacturer to add them to a vehicle. AEC-Q101-compliant components must be able to handle thermal shock and cycling, extreme temperatures, and high humidity.
Identifying automotive circuits requiring protection
All circuits and components are susceptible to damage from electrical transients—regardless of their location within the vehicle. The following list identifies the four most common circuits requiring protection:
1. Legacy two-wire communication buses:
a. Controller Area Network (CAN): This standard allows microcontrollers and devices to communicate within a vehicle without the use of a host computer. CAN systems handle a variety of functions—from power steering to the critical drive-train communications between the engine computer and the transmission.
b. Local Interconnect Network (LIN): This serial network protocol is used for communication between components in the vehicle. LIN buses manage simple electromechanical functions such as moving the power seats and toggling the cruise control.
CAN/LIN buses have a high chance of transient surge exposure, which can cause unprotected CAN/LIN transceivers to fail. Figure 2 illustrates practical strategies for CAN and LIN bus protection.
2. High-speed digital buses: USB/HDMI ports support consumer applications within the vehicle. For instance, the dashboard may contain a USB port for passengers to charge their phone/tablet or play music. HDMI ports are also being used for backup and forward-looking cameras in vehicles. With faster throughput and greater chip sensitivity, these ports require outstanding signal integrity and system reliability. USB/HDMI ports could be damaged by relatively small ESD events and short circuits within the automobile.
3. Wi-Fi communication/SIM socket: This technology allows the vehicle to offer cellular 3G or LTE communication to the passengers. The SIM module is the intermediary part of the circuit that will convert LTE to Wi-Fi, allowing users to connect to phones, tablets, and laptops. The SIM socket requires ESD protection because it will be subjected to human interactions when the module is installed or replaced in the vehicle.
4. High-frequency communication/RF (radio frequency): This technology is supported by short-range RF circuits that enable vehicle-to-vehicle or vehicle-to-road communications. The network allows cars to see each other and communicate from vehicle to vehicle, which may help prevent collisions and enable smart traffic systems. The front ends of the RF amplifiers tend to be very sensitive to ESD. Unbiased RF signals will generate positive and negative polarity voltages on the antenna circuit.
Matching circuit protection solutions to automotive applications
Automotive circuit designers may struggle to find high-quality circuit protection solutions since the number of companies that are capable of developing products that meet the AEC-Q101 standard is limited. When selecting a manufacturer, it is vital to verify the company’s certifications to ensure that its products meet all applicable industry standards. The company should also follow best practices in product design and utilize high-quality manufacturing processes. Table 1 identifies several circuit protection solutions that should be implemented early in the design phase:
Conclusion
Designing robust automotive electronics requires advance planning for the management of environmental and electrical hazards. Successful design starts with understanding the requirements of the ISO 10605 and AEC-Q101 test standards. Adequate protection is required at each layer of electronics since individual modules as well as the completed car will be fully tested for reliability.
The circuit designer should also consider the electrical vulnerabilities of the automotive circuits requiring protection, especially those involving innovative communications and networking. With an understanding of automotive test standards and circuits, the designer can choose the best circuit protection solution for his or her application.
This article was written for Automotive Engineering by James Colby of Littelfuse, Inc.
Author: James Colby
Source: SAE Automotive Engineering Magazine
需要考量ESD保護(hù)的系統(tǒng)。
CAN和LIN公交車的保護(hù)方案圖解。
汽車電路保護(hù)方案的特點(diǎn)。
Littelfuse生產(chǎn)的該款SM24CANA TVS二極管陣列能夠保護(hù)CAN公交車。
Littelfuse生產(chǎn)的該款TPSMA6L系列TVS二極管提供了小范圍需要的電氣性能。
James Colby是Littelfuse有限公司的半導(dǎo)體業(yè)務(wù)發(fā)展經(jīng)理，負(fù)責(zé)定位并開發(fā)戰(zhàn)略增長(zhǎng)市場(chǎng)，以及將新產(chǎn)品推廣到這些市場(chǎng)。他擁有南伊利諾伊大學(xué)（Southern Illinois University）電氣工程理學(xué)士學(xué)位，和凱勒管理研究生院（Keller Graduate School of Management）的MBA學(xué)位。他在Littlefuse公司有15年以上的工作經(jīng)驗(yàn)，在電子設(shè)備行業(yè)有超過23年的從業(yè)經(jīng)驗(yàn)。