Philips AN96116 Technical data
APPLI C ATION NOT E
PCA82C250 / 251
CAN Transceiver
AN96116
Philips Semiconduct or s
PCA82C250 / 251 CAN Transceiver
Appl ica tio n Note
AN96116
Abstract
The PCA82C250 and PCA82C251 are advanced transceiver products for use in automotive and general industrial applications with transf er rates up to 1 Mbit/s. They support the differential bus signal repre sentat ion being
described in the international standard for in-vehicle CAN high-speed app licat ions (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 inform at ion how to use the above-men tion ed transceiver product s 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 prohi bited 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 patent - or other industrial or intellectual property rights.
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Philips Semiconduct or s
PCA82C250 / 251 CAN Transceiver Application Note
AN96116
APPLI C ATION NOT E
PCA82C250 / 251
CAN Transceiver
AN96116
Author(s):
Harald Eisele, Egon Jöhnk
Product Conce pt & Application Laboratory Hamburg,
Germany
Keywords
Transceiver, ISO 11898, Physical Layer,
Slope-Control, Bus Length, PCA82C250, PCA82C251,
Controller Area Network (CAN)
Supersedes Data of 1996 Apri l 17 (AN96001)
Date: 1996 October 23
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Philips Semiconduct or s
PCA82C250 / 251 CAN Transceiver
Appl ica tio n Note
AN96116
Summary
This report is intended to provide basic technical information for the implement ation of the Physical Medium
Attachment in a CAN network according to the ISO 11898 standard, using the transceiver products PCA82C250
and PCA82C251 from Ph ilip s Sem iconductors. These products support bit rate s 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 Semiconduct or s
PCA82C250 / 251 CAN Transceiver
Appl ica tio n Note
AN96116
CONTENTS
1. INTRODUCTION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
2. APPLICATION OF THE PCA8 2C250 AND PC A82C251 . . . . . . . . . . . . . . . . . . . . . . . . . . 8
2.1 Application Examples. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
2.2 Reference Voltage Out put . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
3. OPERA TION MO DE S . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
3.1 High-Speed Mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 2
3.2 Slope Control Mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
3.3 Stand-by Mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
4. SLOPE CONTRO L FUNCTION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14
4.1 Slew Rate Calculation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14
4.2 Bus Length in Slope Control Mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16
5. MAX I MUM BUS L INE LENGT H . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17
5.1 Impact of the Bus Cable Resistance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 7
5.2 Maximum Number of Nodes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19
5.3 E x a mp l e s. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20
6. BUS TERMIN ATION AND TOP OL OG Y ASPEC TS . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22
6.1 Split Termination Conce pt . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2 2
6.2 Multiple Termination Concept . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22
6.3 Single Termination Concept . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23
6.4 Termination Mismatch . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23
6.5 Unterminat ed Cable Drop Lengt h . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2 4
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 L INE LENGT H . . . . . . . . . . . . . . . . . . 28
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Philips Semiconduct or s
PCA82C250 / 251 CAN Transceiver
(page has been left blank intentionally)
Appl ica tio n Note
AN96116
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Philips Semiconduct or s
PCA82C250 / 251 CAN Transceiver
Appl ica tio n Note
AN96116
1. INTRODUCTION
ISO 118 98 [3] is the internati onal stan dard for in-vehicle high-speed comm uni ca tion using the Controller A rea
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 I nterface 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 controlle r products, like the
PCx82C200 from Ph ilip s Semiconduct or s. Connection to the transm ission medium is provided via the Medium
Dependent Interface i.e. a connector used to attach bus nodes to the bus line.
SPECIFICATION IMPLEMENTATIONOSI-LAYER
TO BE SPECIFIED BY
THE SYSTEM DESIGNER
DATA LINK
CAN-PROTOCOL
SPECIFICATION
SCOPE OF ISO 11898
Note: OSI = Open Systems Interconnection (see ISO 7498)
LAYER
PHYSICAL
LAYER
Fig. 1 Layered architecture of CAN
APPLICATION LAYER
MEDIUM ACCESS CONTROL
PHYSICAL MEDIUM ATTACHMENT
MEDIUM DEPENDENT INTERFACE
TRANSMISSION MEDIUM
LOGICAL LINK CONTROL
CAN-CONTROLLER
e.g.
PCx82C200
PHYSICAL SIGNALLING
CAN-TRANSCEIVER
PCA82C250/251
JK512191.GWM
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Philips Semiconduct or s
EI203030
CAN_H
CAN_L
5V
3.5V
1.5V
0V
2.5V
Recessive Dominant Recessive
Time
Voltage
PCA82C250 / 251 CAN Transceiver
Appl ica tio n 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 nomin al supply volta ge of 12 V (PCA82C250)
and 24 V (P CA82C251) respecti ve ly. The y are function ally ident ical and can be used in automot ive and general
industrial applications accordi ng to the relevant standards e.g. the ISO 11898 stand ard [3] and the DeviceNet
Specification [5]. Both the PCA82 C250 and the PCA82C251 can commun icate to one another in one network.
Moreover they are pin- & function-compat ible i.e. they can be used with identical printed circuit boards.
Some main differences between both products are listed in Tabl e 1.
Table 1 M ain differen ces between PCA82C250 and PCA82C251
PCA82C250 PCA82C251
Nominal system supply volta ge 12 V 12V and/or 24 V
Maximum bus term inal D C volt a ge
(0 V < V
< 5.5 V)
CC
−−8V < V
CANL,H
< +18 V −−40 V < V
CANL,H
TM
< +40 V
Maximum transient bus terminal voltage
(ISO 7637)
Minimum transceiver supply voltage f or extended fan
out applications (R
= 45 Ω)
L
−−150 V < V
V
< +100 V −200 V < Vtr < +200 V
tr
> 4.9 V VCC > 4.5 V
CC
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 vo lta ge range. A lso the
PCA82C251 draw s less supply current in the recessive state and provides an enhanced bus output beh aviour in
power-fail situati ons.
Fig. 2 Nominal bus levels according to ISO 1 1898
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Philips Semiconduct or s
PCA82C250 / 251 CAN Transceiver
e.g. PCx82C200
CAN - Contoller
CTX0
CTX1
/ TX1
CRX0
/ TX0
/ RX0
TxD RxD VREF Rs
PCA 82C250/251
CAN Transceiver
CANH CANL
uC
CRX1
/ RX1
Px,y
either connection to an output port pin,
if standby mode shall be possible
or
connection to ground
0V
R
ext
V
CC
GND
+5V
100n
0V
Appl ica tio n Note
AN96116
JK512151.GWM
ISO 11898 Standard
CAN_H
124
Programming of the Output Control Register (example)
Output Control TX0 push-pull, dominant = low e.g. 1A
Fig. 3 Application example of the PCA82C250/251 transceivers
CAN Bus Line
CAN_L
hex
124
2.1 Application 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 V
0.5 × V
nominal. Both transcei ve r products are powe red wi th a nom inal suppl y voltage of +5 V.
CC
The protocol controller outp uts a serial transm it data stream to the TxD input of the trans ceiver. A n internal pullup function sets the TxD input to logic HIGH i.e. the bus out put 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. Otherwi se if a logic LOW-le ve l is applied to
TxD, this activates the bus output stage, t hus generat ing a so-called dom inant signal level on the bus lin e (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 nom inal volt age in the domin ant sta te is 3.5 V for the CAN_H line and
1.5 V for the CAN_L lin e.
provides an output voltage of
REF
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