eiver 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. Philips Semiconductors
Application note
AN2005
AU5790 Single wire CAN transceiver
i
2001 Apr 16
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 in CAN Node Architecture
4
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
3.
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 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
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Philips Semiconductors
Application note
AN2005
AU5790 Single wire CAN transceiver
2
2001 Apr 16
1.
INTRODUCTION
The 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 functions and benefits, and to guide the user in applying the 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.
1
11
3
4
0 .. 8 BYTES
15
1 1
7
1
11
2
18
3
4
15
1
1
1
7
0 .. 8 BYTES
STANDARD DATA FORMAT
EXTENDED DATA FORMAT
IDENTIFIER
IDENTIFIER
IDENTIFIER
DLC
DLC
DATA
DATA
CRC
ACK
EOF
CRC
ACK
EOF
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 t
bit,
consists of three non-overlapping segments: SYNC_SEG,
TSEG1, and TSEG2, with time duration t
SYNC_SEG,
t
seg1,
and

t
seg2,
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, t
Q,
is derived from the oscillator. The sample point
usually is located at the end of TSEG1.
SYNCH_SEG
TSEG1
TSEG2
SAMPLE POINT
t
SYNCH_SEG
t
SEG1
t
SEG2
NBT, t
BIT
SL01258
Figure 2.
CAN bit time definition Philips Semiconductors
Application note
AN2005
AU5790 Single wire CAN transceiver
2001 Apr 16
3
Within CAN each node must synchronize to each others 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 others 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:
t
prop
(max) < t
bit
t
seg2
( 25t
bit
t
seg2
)* f (1)
t
prop
(max) < t
bit
t
seg2
( 25t
bit
t
seg2
)* f + t
prop
(min)/2 t
Q
(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* t
Q
.
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, 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. Node 3 finally wins bus access and continues message transmi