PDF AN96116 Data sheet ( Hoja de datos )

Número de pieza	AN96116
Descripción	CAN Transceiver
Fabricantes	Philips
Logotipo
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No Preview Available ! www.DataSheet4U.com APPLICATION NOTE PCA82C250 / 251 CAN Transceiver AN96116 DataSheet4U.com DataShee DataSheet4U.com DataSheet4 U .com DataSheet4U.com 1 page www.DataSheet4U.com Philips Semiconductors PCA82C250 / 251 CAN Transceiver Application Note AN96116 CONTENTS 1. INTRODUCTION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7 2. APPLICATION OF THE PCA82C250 AND PCA82C251 . . . . . . . . . . . . . . . . . . . . . . . . . . 8 2.1 Application Examples . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9 2.2 Reference Voltage Output . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11 3. OPERATION MODES . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12 3.1 High-Speed Mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12 3.2 Slope Control Mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12 3.3 Stand-by Mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13 4. SLOPE CONTROL FUNCTION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14 4.1 Slew Rate Calculation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14 4.2 Bus Length in Slope Control Mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16 5. MAXIMUM BUS LINE LENGTH . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17 5.1 Impact of the Bus Cable Resistance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17 5.2 Maximum Number of Nodes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19 5.3 Examples . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20 6. et4U.com BUS TERMINATION AND TOPOLOGY ASPECTS . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22 6.1 Split Termination Concept . . . . D. a.ta.S.he. e.t4.U.co. m. . . . . . . . . . . . . . . . . . . . . . . . 22 6.2 Multiple Termination Concept . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22 6.3 Single Termination Concept . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23 6.4 Termination Mismatch . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23 6.5 Unterminated Cable Drop Length . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24 DataShee 7. CONCLUSION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25 8. LIST OF REFERENCES . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25 APPENDIX 1 ABBREVIATIONS AND DEFINITIONS . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26 APPENDIX 2 CALCULATION OF THE VOLTAGE AT THE INPUT OF A NODE . . . . . . . . . . . . . . 27 APPENDIX 3 CALCULATION OF THE MAXIMUM BUS LINE LENGTH . . . . . . . . . . . . . . . . . . 28 DataSheet4U.com DataSheet4 U .com 5 DataSheet4U.com 5 Page www.DataSheet4U.com Philips Semiconductors PCA82C250 / 251 CAN Transceiver Application Note AN96116 The receiver comparator converts the differential bus signal to a logic level signal which is output at RxD. The serial receive data stream is provided to the bus protocol controller for decoding. The receiver comparator is always active i.e. it monitors the bus while the bus node is transmitting a message. This is required e.g. for safety reasons and to support the non-destructive bit by bit contention scheme of CAN. Some controller products pro- vide an analog receive interface (RX0, RX1). In that case RX0 usually needs to be connected to the RxD output and RX1 needs to be biased to an appropriate voltage level. This can be done e.g. by using the VR EF output (see Fig. 3) or by using a resistive voltage divider (see Fig. 4). In Fig. 3 the transceiver is directly connected to the protocol controller and its application circuitry. In cases where galvanic isolation is desired, optocouplers can be placed e.g. between the transceiver and the protocol controller as shown in Fig. 4. When using optocouplers one has to pay attention to choose the right default state when the circuitry at the protocol controller side of the isolation is not powered. In such a case the optocoupler being attached to TxD will be “dark” i.e. LED switched off. When this optocoupler is off/dark, then a logic HIGH-level has to be output to the TxD input of the transceiver for fail-safe purpose. Also if using optocouplers one may con- sider to attach the Rs mode control input to an active-high reset signal, e.g. to disable the transceiver when the local transceiver supply voltage is not OK e.g. during ramp-up and -down. However using optocouplers generally increases the so-called loop delay of a bus node, if placed between the transceiver and the protocol controller. The signal has to pass these devices twice per node, i.e. transmit and receive path, which effectively decreases the maximum achievable bus length at a given bit rate. This fact has to be considered when calculating the maximum achievable bus length due to propagation delays in a CAN net- work. For more details please refer e.g. to [4]. et4U.com 2.2 Reference Voltage Output DataSheet4U.com The PCA82C250/251 provides a reference voltage output VR EF, which may be used e.g. to bias one of the inputs of a CAN protocol controller´s differential input comparator as shown in Fig. 3. In other cases a reference voltage may be generated locally at the protocol controller input as shown e.g. in Fig. 4. Which solution is appro- priate in a system depends on the application and the bus input structure of the protocol controller product. DataShee DataSheet4U.com DataSheet4 U .com 11 DataSheet4U.com 11 Page

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