Philips AN96116 Technical data

APPLICATION NOTE

PCA82C250 / 251

CAN Transceiver

AN96116

Philips Semiconductors

PCA82C250 / 251 CAN Transceiver	Application Note
	AN96116

Abstract

The PCA82C250 and PCA82C251 are advanced transceiver products for use in automotive and general industrial applications with transfer rates up to 1 Mbit/s. They support the differential bus signal representation being described in the international standard for in-vehicle CAN high-speed applications (ISO 11898). Controller Area Network (CAN) is a serial bus protocol being primarily intended for transmission of control related data between a number of bus nodes.

This application note provides information how to use the above-mentioned transceiver products and discusses several topics of interest like slope control mode, stand-by mode, bus length and maximum number of bus nodes per network.

© Philips Electronics N.V. 1996

All rights are reserved. Reproduction in whole or in part is prohibited without the prior written consent of the copyright owner.

The information presented in this document does not form part of any quotation or contract, is believed to be accurate and reliable and may be changed without notice. No liability will be accepted by the publisher for any consequence of its use. Publication thereof does not convey nor imply any license under patentor other industrial or intellectual property rights.

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Philips Semiconductors

PCA82C250 / 251 CAN Transceiver	Application Note
	AN96116

APPLICATION NOTE

PCA82C250 / 251

CAN Transceiver

AN96116

Author(s):

Harald Eisele, Egon Jöhnk

Product Concept & Application Laboratory Hamburg,

Germany

Keywords

Transceiver, ISO 11898, Physical Layer,

Slope-Control, Bus Length, PCA82C250, PCA82C251,

Controller Area Network (CAN)

Supersedes Data of 1996 April 17 (AN96001)

Date: 1996 October 23

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Philips Semiconductors

PCA82C250 / 251 CAN Transceiver	Application Note
	AN96116

Summary

This report is intended to provide basic technical information for the implementation of the Physical Medium Attachment in a CAN network according to the ISO 11898 standard, using the transceiver products PCA82C250 and PCA82C251 from Philips Semiconductors. These products support bit rates up to 1 Mbit/s over a two-wire differential bus line, which is the transmission medium being specified by the ISO 11898 standard.

The report provides typical application circuit diagrams with and without electrical isolation and discusses several topics in more detail like slope control mode, stand-by mode, maximum bus length and maximum number of bus nodes per network.

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Philips Semiconductors

PCA82C250 / 251 CAN Transceiver	Application Note
	AN96116

CONTENTS

1.INTRODUCTION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7

2.APPLICATION OF THE PCA82C250 AND PCA82C251 . . . . . . . . . . . . . . . . . . . . . . . . . . 8

2.1Application Examples . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9

2.2Reference 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

4.2Bus Length in Slope Control Mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16

5.MAXIMUM BUS LINE LENGTH . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17

5.1Impact of the Bus Cable Resistance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17

5.2Maximum Number of Nodes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19

5.3Examples . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20

6.BUS TERMINATION AND TOPOLOGY ASPECTS . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22

6.1Split Termination Concept . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22

6.2	Multiple Termination Concept	. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .	22
6.3	Single Termination Concept	. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .	23

6.4Termination Mismatch . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23

6.5	Unterminated Cable Drop Length . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24

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

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Philips Semiconductors

PCA82C250 / 251 CAN Transceiver	Application Note
	AN96116
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Philips Semiconductors

PCA82C250 / 251 CAN Transceiver	Application Note
	AN96116

1.INTRODUCTION

ISO 11898 [3] is the international standard for in-vehicle high-speed communication using the Controller Area Network (CAN) bus protocol. The scope of this standard essentially is to specify the so-called data link layer and physical layer of the communication link. The physical layer is subdivided into three sublayers as shown in Fig. 1. These are

∙	Physical Signalling	bit coding, timing and synchronization
∙	Physical Medium Attachment	driver and receiver characteristics
∙	Medium Dependent Interface	bus connector

This report focuses on the implementation of the Physical Medium Attachment sublayer using the transceivers PCA82C250 [1] and PCA82C251 [2] from Philips Semiconductors. The implementation of the Physical Signalling sublayer and the Data Link Layer is typically performed by integrated protocol controller products, like the PCx82C200 from Philips Semiconductors. Connection to the transmission medium is provided via the Medium Dependent Interface i.e. a connector used to attach bus nodes to the bus line.

SPECIFICATION

OSI-LAYER

IMPLEMENTATION

TO BE SPECIFIED BY

APPLICATION LAYER

THE SYSTEM DESIGNER

		LOGICAL LINK CONTROL
	DATA LINK		CAN-CONTROLLER
CAN-PROTOCOL	LAYER	MEDIUM ACCESS CONTROL	e.g.
SPECIFICATION			PCx82C200
		PHYSICAL SIGNALLING
	PHYSICAL	PHYSICAL MEDIUM ATTACHMENT	CAN-TRANSCEIVER
SCOPE OF ISO 11898	LAYER		PCA82C250/251
		MEDIUM DEPENDENT INTERFACE
		TRANSMISSION MEDIUM	JK512191.GWM

Note: OSI = Open Systems Interconnection (see ISO 7498)

Fig. 1 Layered architecture of CAN

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Philips Semiconductors

PCA82C250 / 251 CAN Transceiver	Application Note
	AN96116

2.APPLICATION OF THE PCA82C250 AND PCA82C251

The PCA82C250/251 transceiver products basically provide interfacing between a protocol controller and a physical transmission line. They are designed to transmit data with a bit rate of up to 1 Mbit/s over a two-wire differential voltage bus line as described in the ISO 11898 standard. Their general features are listed in the data sheets (see [1] and [2]).

Both devices are designed for the use in CAN bus systems with a nominal supply voltage of 12 V (PCA82C250) and 24 V (PCA82C251) respectively. They are functionally identical and can be used in automotive and general industrial applications according to the relevant standards e.g. the ISO 11898 standard [3] and the DeviceNetTM Specification [5]. Both the PCA82C250 and the PCA82C251 can communicate to one another in one network.

Moreover they are pin- & function-compatible i.e. they can be used with identical printed circuit boards.

Some main differences between both products are listed in Table 1.

Table 1 Main differences between PCA82C250 and PCA82C251

		PCA82C250	PCA82C251
	Nominal system supply voltage	12 V	12V and/or 24 V
	Maximum bus terminal DC voltage	−8 V < VCA NL , H < +18 V	−40 V < VC AN L, H < +40 V
	(0 V < VC C < 5.5 V)
	Maximum transient bus terminal voltage	−150 V < Vt r < +100 V	−200 V < Vtr < +200 V
	(ISO 7637)
	Minimum transceiver supply voltage for extended fan	VCC > 4.9 V	VC C > 4.5 V
	out applications (RL = 45 Ω)

For general industrial applications the PCA82C251 is recommended to be employed as to e.g. its higher breakdown voltage and its capability to drive loads down to 45 Ω over the whole supply voltage range. Also the PCA82C251 draws less supply current in the recessive state and provides an enhanced bus output behaviour in power-fail situations.

Voltage
5V
3.5V	CAN_H
2.5V
1.5V	CAN_L
0V		EI203030
		Time
Recessive	Dominant	Recessive

Fig. 2 Nominal bus levels according to ISO 11898

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Philips Semiconductors

PCA82C250 / 251 CAN Transceiver	Application Note
	AN96116

uC

e.g. PCx82C200

CAN - Contoller

CTX1CTX0 CRX0 CRX1

Px,y

/ TX1 / TX0 / RX0

/ RX1

either connection to an output port pin,

if standby mode shall be possible

or

connection to ground

0V

Rext

TxD RxD

VREF

Rs

+5V

PCA 82C250/251 VCC

CAN Transceiver

100n

CANH CANL

GND

0V

JK512151.GWM

ISO 11898 Standard

CAN_H

124

CAN Bus Line

CAN_L

124

Programming of the Output Control Register (example)

Output Control

TX0 push-pull, dominant = low

e.g. 1Ah e x

Fig. 3 Application example of the PCA82C250/251 transceivers

2.1Application Examples

A typical application of the PCA82C250/251 transceiver is shown in Fig. 3. A protocol controller is connected to the transceiver via a serial data output line (TX) and a serial data input line (RX). The transceiver is attached to the bus line via its two bus terminals CANH and CANL, which provide differential receive and transmit capability. The input Rs is used for mode control purpose. The reference voltage output VR EF provides an output voltage of 0.5 × VC C nominal. Both transceiver products are powered with a nominal supply voltage of +5 V.

The protocol controller outputs a serial transmit data stream to the TxD input of the transceiver. An internal pullup function sets the TxD input to logic HIGH i.e. the bus output driver is passive by default. In this so-called recessive state (see Fig. 2) the CANH and CANL inputs are biased to a voltage level of 2.5 V nominal via receiver input networks with an internal impedance of 17 kΩ typical. Otherwise if a logic LOW-level is applied to TxD, this activates the bus output stage, thus generating a so-called dominant signal level on the bus line (see Fig. 2). The output driver consists of a source and a sink output stage. CANH is attached to the source output and CANL to the sink output stage. The nominal voltage in the dominant state is 3.5 V for the CAN_H line and 1.5 V for the CAN_L line.

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