AU5790 AN2005 SL01257 SL01258 ID-23 ID-20 SL01259 SL01260 SJA1000 SL01261 - Datasheet Archive

 

The AU5790 single wire CAN transceiver is a line transceiver intended primarily for in-vehicle class B multiplexing applications.

 

INTEGRATED CIRCUITS The AU5790 AU5790 single wire CAN transceiver is a line transceiver intended primarily for in-vehicle class B multiplexing applications. This device provides interfacing between a CAN data link controller and a single wire physical bus system with ground return. AN2005 AN2005 AU5790 AU5790 Single wire CAN transceiver Bin Lin Philips Semiconductors 2001 Apr 16 Philips Semiconductors Application note AU5790 AU5790 Single wire CAN transceiver AN2005 AN2005 CONTENTS 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2 2. Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2 2.1 CAN . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2 2.1.1 Bit Timing and Propagation Delay . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2 2.1.2 Arbitration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3 2.2 Single Wire CAN Transceiver . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4 2.3 AU5790 AU5790 in CAN Node Architecture . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4 3. AU5790 AU5790 Features . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5 3.1 Features List . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5 3.2 Block Diagram and Function Description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6 3.3 Operating Mode and Control . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7 3.3.1 Sleep Mode and Power Management . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7 3.3.2 Wake-up Mode and Bus Signal Levels . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8 3.3.3 High Speed Data Download . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9 3.3.4 Normal Mode and Wave-shaping . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9 3.4 Loss of Ground Protection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10 4. Application . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12 4.1 AU5790 AU5790 Application Circuit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12 4.2 Node and Bus Load Effects . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14 4.2.1 Basic Node Load . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14 4.2.2 CAN Bus Line Load . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14 4.2.3 An Example of CAN Network . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14 4.3 Thermal Management . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15 4.3.1 Thermal Resistance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15 4.3.2 Power Dissipation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18 4.3.3 Selecting a Package and Board . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19 2001 Apr 16 i Philips Semiconductors Application note AU5790 AU5790 Single wire CAN transceiver AN2005 AN2005 1. INTRODUCTION The AU5790 AU5790 single wire CAN transceiver is a line transceiver intended primarily for in-vehicle class B multiplexing applications. This device provides interfacing between a CAN data link controller and a single wire physical bus system with ground return. This application note is intended to explain AU5790 AU5790 functions and benefits, and to guide the user in applying the AU5790 AU5790 in a vehicle network environment. 2. OVERVIEW 2.1 CAN The Controller Area Network (CAN) is a serial communication protocol widely used in Automotive and Industrial applications for interconnecting control units, sensors, actuators, etc. There are two relevant CAN message formats in use today. One is the standard message format which is defined in CAN Specification 1.2. The other one is the extended message format which is described in CAN Specification 2.0 Part B. Primarily the two differ in that the standard message frame has 11 identifier bits, where the extended frame has 29 identifier bits. STANDARD DATA FORMAT IDENTIFIER 1 11 DLC 3 DATA 0 . 8 BYTES 4 CRC ACK 15 1 1 EOF ­ 7 EXTENDED DATA FORMAT IDENTIFIER 1 11 IDENTIFIER 2 18 DLC 3 4 DATA CRC 0 . 8 BYTES ACK 15 1 1 EOF 1 7 SL01257 SL01257 Figure 1. CAN message frames 2.1.1 Bit Timing and Propagation Delay By the CAN bit timing definition, the Nominal Bit Time (NBT), with time duration tbit, consists of three non-overlapping segments: SYNC_SEG, TSEG1, and TSEG2, with time duration tSYNC_SEG, tseg1, and tseg2, respectively, as shown in Figure 2. Each of these segments may be programmed to be an integral number of the Time Quantum (TQ), whose time duration, tQ, is derived from the oscillator. The sample point usually is located at the end of TSEG1. SYNCH_SEG TSEG1 TSEG2 SAMPLE POINT tSYNCH_SEG tSEG1 tSEG2 NBT, tBIT SL01258 SL01258 Figure 2. CAN bit time definition 2001 Apr 16 2 Philips Semiconductors Application note AU5790 AU5790 Single wire CAN transceiver AN2005 AN2005 Within CAN each node must synchronize to each other's message on the first recessive to dominant edge of the message and all the other recessive to dominant edges in the message waveform. Because each node has its own clock reference, the oscillator tolerance, f, will affect the bit time and the sample time, so f has big impact on the synchronization. Meanwhile, CAN supports arbitration and in-frame acknowledgment, which means after sending out a data bit the transceiver needs to read back the bus level, so the propagation delay between nodes in the network must be limited to guarantee synchronization. The propagation delay from node A to node B includes all the device delays in the transmission path from A to B, CAN controller A delay time, transceiver A transmit delay, transceiver B receive delay, and bus line delay, etc. Since all nodes must receive each other's signal, and synchronize to it, then send them back during arbitration, the total propagation delay in the network should be the round trip delay. Dietmayer and Overberg analyzed CAN bit timing requirements in detail in their SAE technical paper #970295[1]. By summarizing their analysis, we can find that in order to guarantee CAN bit time requirement, the total propagation delay has to satisfy following equations: tprop(max) < tbit ­ tseg2 ­ ( 25tbit ­ tseg2)* f (1) tprop(max) < tbit ­ tseg2 ­ ( 25tbit ­ tseg2)* f + tprop(min)/2 ­ tQ (1- f) (2) The requirement on Equation (1) is more severe than that on Equation (2) if the minimum propagation delay is larger than 2* tQ. 2.1.2 Arbitration If no device is transmitting a message, the network bus is in a recessive state, and any device may start to transmit a message. If more than one device starts to transmit a message at the same time, only one device gets bus access successfully by bit arbitration using the identifier. All devices on the bus are connected to the bus in a wired OR configuration. During arbitration, every device compares the read-back bus level with the transmitted data level. If these levels are the same, the transmission continues. If a device sends a recessive level, and reads back a dominant level, it has lost arbitration and has to stop sending any more bits, and becomes a receiver. The following figure shows an arbitration example. Node 1, 2, and 3 start to send out message at the same time. At bit ID-23 ID-23, node 2 sends a recessive level, but the readback bus level is dominant, thus node 2 loses arbitration and becomes a receiver. Node 1 loses its arbitration at bit ID-20 ID-20. Node 3 finally wins bus access and continues message transmission. ARBITRATION CONTROL DATA ID 28 . 18 R T R S O F RECEIVE * NODE 1 RECEIVE NODE 2 * NODE 3 DOMINANT RECESSIVE BUS-LEVEL * = ARBITRATION LOSS BITS NOT SENT SL01259 SL01259 Figure 3. CAN bus arbitration 2001 Apr 16 3 Philips Semiconductors Application note AU5790 AU5790 Single wire CAN transceiver AN2005 AN2005 2.2 Single Wire CAN Transceiver Dual wire CAN transceivers are being extensively used in high speed (~1 Mbps) and medium speed (~125 Kbps) applications where data transfer rate is the primary goal. The two wire approach lends itself well to high speed transmission while taking advantage of the inherent noise cancellation associated with balanced twisted pair medium implementations. In cost sensitive applications as in body electronics, where data rates can be reduced below 50 Kbps, single wire solutions provide a good speed/cost alternative. In single wire systems EMC must be dealt with in the transceiver through wave-shaping to reduce frequency components above the data rate. The fundamental difference in network topology between the various types of transceivers offered by Philips is shown below. A ­ HIGH SPEED B ­ FAULT TOLERANT HS C ­ SINGLE WIRE (AU5790 AU5790) LS HS SW LS HS SW LS Bus Voltage Bus Voltage Bus Voltage 5 4 CAN_H 4 SW CAN_L 1 0 CAN_H 5 4 2,5 1 CAN_L t Recessive Dominant Recessive t Recessive Dominant Recessive CAN_H 0 t Recessive Dominant Recessive SL01260 SL01260 Figure 4. CAN transceivers comparison Figure 4(a) is a high speed CAN network with termination resistor to set the recessive level. In Figure 4(b) a fault tolerant CAN network eliminates termination resistors and permits communication to continue under some fault conditions. Resistors at each node set the recessive level. The single wire CAN network shown at Figure 4(c) reduces the number of wires, and number of connectors or wire splices in half while also reducing wiring harness weight. Resistors at each node set the recessive level. 2.3 AU5790 AU5790 in CAN Node Architecture A CAN node can be subdivided into three layers, as shown in Figure 5. The object layer is concerned with message filtering as well as status and message handing. The transfer layer represents the kernel of the CAN protocol. It presents messages received to the object layer and accepts message to be transmitted from the object layer. The transfer layer is responsible for bit timing and synchronization, message framing, arbitration, acknowledgement, error detection and signalling, and fault confinement. The physical layer actually transmits signals. The AU5790 AU5790 is a physical layer interface device in a CAN structure. 2001 Apr 16 4 Philips Semiconductors Application note AU5790 AU5790 Single wire CAN transceiver AN2005 AN2005 APPLICATION INTERFACE µC OBJECT LAYER TRANSFER LAYER STAND-ALONE CAN CONTROLLER (SJA1000 SJA1000) AU5790 AU5790 PHYSICAL LAYER CAN TRANSCEIVER SINGLE WIRE CAN BUS SL01261 SL01261 Figure 5. CAN node structure 3. AU5790 AU5790 FEATURES 3.1 Feature list · Supports in-vehicle class B multiplexing via a single bus line with ground return · 33 kbps CAN bus transmission speed · 83 kbps high-speed download mode · Up to 32 bus nodes · 70 µA power consumption in sleep mode · Low electromagnetic emission due to output wave-shaping · Direct battery operation with protection against load dump, jump start and transients · Bus terminal protected against short-circuits and transients in the automotive environment · Built in loss of ground protection · Thermal overload protection · Wake-up feature supports communication between control units even when network is in sleep state · ± 8KV ESD protection on bus and battery pins 2001 Apr 16 5 Philips Semiconductors Application note AU5790 AU5790 Single wire CAN transceiver AN2005 AN2005 3.2 Block Diagram and Function Description The AU7590 AU7590 consists of several functional blocks shown in the block diagram below. BATTERY (+12V) BAT 1 VOLTAGE TEMP. REFERENCE PROTECTION L TxD CAN CONTROLLER AND µC NSTB OUTPUT BUFFER 7 BUS CANH CUL 3 (Mode 0) MODE BUS RECEIVER CONTROL 6 EN (Mode 1) RT RxD 5 4 LOSS OF GROUND PROTECTION RTH (LOAD) AU5790 AU5790 8 GND SL01306 SL01306 Figure 6. AU5790 AU5790 block diagram The protocol controller feeds the transmit data stream to the transceiver's TxD input. The AU5790 AU5790 transceiver converts the TxD data input to a bus signal with controlled slew rate and wave-shaping to minimize electromagnetic emissions. The bus output signal is transmitted via the CANH in/output pin, which is connected to the physical bus medium. If TxD is low, then a typical voltage of 4 V is output at the CANH pin. If TxD is high then the CANH output is pulled passive low via the local bus load resistance RT. The physical bus lines for all transceivers on the bus are connected in a wired-OR configuration, therefore the bus will be at a dominant level unless all nodes in network are passive. To provide protection against a disconnection of the module ground wire the resistor RT is connected to the RTH pin of the AU5790 AU5790. The RTH pin is connected to ground via the loss of ground protection circuit in the AU5790 AU5790. By providing this switched ground pin, no current can flow from the floating module ground to the bus via load resistor RT. The bus receiver detects the data stream at the bus line. The data signal is output at the RxD pin, which should be connected to a CAN controller. If the bus level is recessive, i.e. all transmitters are passive, then RxD is floating or High with external pull-up resistance. If the bus 2001 Apr 16 6 Philips Semiconductors Application note AU5790 AU5790 Single wire CAN transceiver AN2005 AN2005 level is dominant, i.e. at least one transmitter is active, then RxD is Low. The RxD is an open drain output, and needs an external pull-up resistance. To insure the RxD has the same voltage swing as other digital signal, the RxD pin should be pulled-up to the digital power supply Vcc. The AU5790 AU5790 provides appropriate high frequency filtering to ensure minimum susceptibility against electromagnetic interference. Further enhancement is possible by applying an external inductor L and a capacitor CUL at the CANH pin as shown in Figure 6. The AU5790 AU5790 features special robustness at its BAT and CANH pins. Hence the device is well suited for applications in the automotive environment. The BAT input is protected against 40V load dump, jump start conditions and all the conventional Automotive transients as defined in SAE J1113/ISO7637 J1113/ISO7637. In addition the CANH output pin is protected against ESD transients of at least 8KV without any external device protection. Protection against wiring fault conditions e.g. short circuit to ground or battery voltage is also included in the design. A thermal protection shutdown function with hysteresis is incorporated aimed at protecting the device against system fault conditions leading to excessive operating junction temperature. In case the chip junction temperature reaches the trip point (>155 _C), the temperature protection circuit will turn-off the transmit function. The transmit function is available again after a small decrease of the junction temperature. The thermal shutdown hysteresis is about 5 _C. NSTB and EN are mode control input pins. They are typically provided by a controller device. The AU5790 AU5790 has four operation modes: sleep mode, wake-up mode, high-speed transmission mode, and normal transmission mode. 3.3 Operating Mode and Control The microcontroller controls the transceiver's operating mode via the EN and NSTB pins. It is the microcontroller's responsibility to insure that the mode changes take place between the message frames. The following is the mode control summary table. Table 1. Mode Control Summary NSTB 0 0 1 1 EN 0 1 0 1 TXD don't care TXD-data TXD-data TXD-data Description sleep mode wake-up mode high-speed mode normal mode CANH 0V 0 V, 12 V 0 V, 4 V 0 V, 4 V RX D float(high) bus state bus state bus state Times that the transceiver needs to change its operation mode are shown in following table. Table 2. Mode Switching Time From Mode Normal Normal Normal High speed Wake-up Sleep To Mode High speed Wake-up Sleep Normal Normal Normal Mode Switching Time (µs)