Protecting Your CANProtecting Your CAN - microchip.com

1 microchip Technology : October 2006 CAN ProtectionPage 1 2006 microchip Technology Incorporated. All Rights Reserved. Introduction to Controller Area Network (CAN)1 Protecting Your CANP rotecting Your CANP rotecting Your CANC ontroller Area Network Physical Layer ProtectionController Area Network Controller Area Network Physical Layer ProtectionPhysical Layer ProtectionHello, and welcome to the WebSeminar on the EMI and ESD protection for the CAN Bus. My name is Pat Richards. I am an Applications Engineer in the Analog and Interface Products Division.

2 So let s get Technology : October 2006 CAN ProtectionPage 2 2006 microchip Technology Incorporated. All Rights Reserved. Introduction to Controller Area Network (CAN)2 TopicsTopicsTopicsOWhy Does the CAN Bus Need Protecting ?OCommon Protection MethodsOSummaryOOWhy Does the CAN Bus Need Protecting ?Why Does the CAN Bus Need Protecting ?OOCommon Protection MethodsCommon Protection MethodsOOSummarySummaryToday we will be discussing protection methods for the Controller Area Network, or the CAN Bus.

3 We will answer the question, Why does the CAN Bus need extra protection? We will then identify some common protection methods, which include cabling, filters, common mode chokes, split termination, MOVs, TVSs and then we will finish with a brief Technology : October 2006 CAN ProtectionPage 3 2006 microchip Technology Incorporated. All Rights Reserved. Introduction to Controller Area Network (CAN)3 TopicsTopicsTopicsOWhy Does the CAN Bus Need Protecting ?OCommon Protection MethodsOSummaryOOWhy Does the CAN Bus Need Protecting ?

4 Why Does the CAN Bus Need Protecting ?OOCommon Protection MethodsCommon Protection MethodsOOSummarySummarySo, why does the CAN Bus need extra protection anyway? Doesn t the transceiver provide adequate protection? microchip Technology : October 2006 CAN ProtectionPage 4 2006 microchip Technology Incorporated. All Rights Reserved. Introduction to Controller Area Network (CAN)4 Noisy, Harsh EnvironmentsNoisy, Harsh EnvironmentsNoisy, Harsh EnvironmentsOCAN is used in automotive and industrial applicationsONodes must survive high energy transientsOLoad dumpOInductive load switchingORelay noiseOIgnition system noiseOAnd short circuit conditionsOOCAN is used in automotive and industrial CAN is used in automotive and industrial applicationsapplicationsOONodes must survive high energy transientsNodes must survive high energy transientsOOLoad dumpLoad dumpOOInductive load switchingInductive load switchingOORelay noiseRelay

5 NoiseOOIgnition system noiseIgnition system noiseOOAnd short circuit conditionsAnd short circuit conditionsCAN was originally developed for data communications in the automotive industry. The industry is a noisy, harsh nodes are subject to high energy transients such as load dump, inductive load switching, relay noise, ignition switching, most popular physical layer in CAN is specified by ISO ISO 11898 compatible transceivers do a good job of filtering out noise, which are coupled on the bus, and Protecting the node from energy spikes and short circuit conditions.

6 For example, the MCP2515 can withstand shorts of + or 42 volts on the CAN bus and can withstand transient energy spikes of + or 250 volts without damage to the , the differential signaling inherent in CAN helps to filter out noise. However, in some systems the environment is harsh enough that extra protection and/or extra filtering is needed to protect the node and ensure clean Technology : October 2006 CAN ProtectionPage 5 2006 microchip Technology Incorporated. All Rights Reserved. Introduction to Controller Area Network (CAN)5 TopicsTopicsTopicsOWhy Does the CAN Bus Need Protecting ?

7 OCommon Protection MethodsOSummaryOOWhy Does the CAN Bus Need Protecting ?Why Does the CAN Bus Need Protecting ?OOCommon Protection MethodsCommon Protection MethodsOOSummarySummaryThe rest of the presentation we will look at some of the common protection methods for the CAN Technology : October 2006 CAN ProtectionPage 6 2006 microchip Technology Incorporated. All Rights Reserved. Introduction to Controller Area Network (CAN)6 Transceivers Provide Some ProtectionTransceivers Provide Some Transceivers Provide Some ProtectionProtectionOISO 11898 requires:OShort circuit protection = to +32 VOTransient protection = -150V to +100 VOMCP2551 protection (bus pins)OShort circuit protection = 42 VOTransient protection = 250 VOOISO 11898 requires:ISO 11898 requires.

8 OOShort circuit protection = Short circuit protection = to + to +32 VOOT ransient protection = Transient protection = --150V to +100V150V to +100 VOOMCP2551 protection (bus pins)MCP2551 protection (bus pins)OOShort circuit protection = Short circuit protection = 42V42 VOOT ransient protection = Transient protection = 250V250 VAs mentioned earlier, ISO 11898 is by far the most popular physical layer for CAN. The spec requires that the transceiver be able to withstand short circuit conditions on the bus of -3 volts to +32 volts and transient energy surges of -150 volts to 100 volts.

9 Compatible transceivers must meet these s MCP2551 exceeds the spec. On that device the short circuit protection is + or -42 volts and transient protection of + or -250 , sometimes extra protection is still needed to further improve the robustness of the CAN Technology : October 2006 CAN ProtectionPage 7 2006 microchip Technology Incorporated. All Rights Reserved. Introduction to Controller Area Network (CAN)7 Shielded Twisted Pair CableShielded Twisted Pair CableShielded Twisted Pair CableOShielded cable reduces radiated interference from introducing noise on the common mode voltageOTwisted pair essentially equalizes the noise across both wiresONoise distributed equally is invisible to the differential busOOShielded cable reduces radiated interference from Shielded cable reduces radiated interference from introducing noise on the common mode voltageintroducing noise on the common mode

10 VoltageOOTwisted pair essentially equalizes the noise across Twisted pair essentially equalizes the noise across both wiresboth wiresOONoise distributed equally is invisible to the Noise distributed equally is invisible to the differential busdifferential busTwisted pair wiring is a common method to reduce the effects of radiated emissions from external , twisted pair reduces the chance of noise coupling on the bus lines, and noise that does couple on the line is equally distributed to both wires and is effectively invisible to the differential twisted pair solution is basically a filter and does not provide any protection from high energy electrical Technology : October 2006 CAN ProtectionPage 8 2006 microchip Technology Incorporated.