TJA1040 high speed CAN transceiver

AN10211
TJA1040 high speed CAN transceiver
Rev. 02 — 10 November 2006
Application note
Document information
Info
Content
Keywords
Controller Area Network (CAN), ISO11898, Transceiver, Physical Layer,
TJA1040, TJA1041, TJA1050, PCA82C250/C251
Abstract
The TJA1040 is an advanced high speed CAN transceiver for use in
automotive and general industrial applications. It supports the differential
bus signal representation described in the international standard for
in-vehicle high speed CAN applications (ISO11898). CAN (Controller Area
Network) is the standard protocol for serial in-vehicle bus communication,
particularly for Engine Management and Body Multiplexing.
The TJA1040 provides a Standby mode, as known from its functional
predecessors PCA82C250 and PCA82C251, but with significantly
reduced power consumption. Besides the excellent low-power behavior
the TJA1040 offers several valuable system improvements. Highlights are
the absolute passive bus behavior if the device is unpowered as well as
the excellent EMC performance.
AN10211
NXP Semiconductors
TJA1040 high speed CAN transceiver
Revision history
Rev
Date
Description
02
20061110
Updated version
01
20030221
•
The format of this application note has been redesigned to comply with the new identity
guidelines of NXP Semiconductors.
•
•
•
•
Legal texts have been adapted to the new company name where appropriate.
Update of Section 5.2.1 “Common mode choke”.
Update of Section 5.2.3 “ESD protection”.
Update of Section 6 “Pin FMEA”.
Initial version
Contact information
For additional information, please visit: http://www.nxp.com
For sales office addresses, please send an email to: [email protected]
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TJA1040 high speed CAN transceiver
1. Introduction
The high speed CAN transceiver TJA1040 Ref. 1 from NXP Semiconductors provides the
physical link between the protocol controller and the physical transmission medium
according to ISO11898 (Ref. 2 , Ref. 3 and Ref. 4) and SAE J2284 Ref. 5. This ensures
interoperability with other ISO11898 compliant transceiver products.
Since the TJA1040 is based on the same technology as the high speed CAN transceiver
TJA1050 Ref. 6 it is processed in the advanced Silicon-on-Insulator (SOI) technology.
Compared to its functional predecessors PCA82C250 (C250) Ref. 7 and PCA82C251
(C251) Ref. 8 the TJA1040 shows a reduction of about 20 dB in electromagnetic emission
(EME). Additionally the electromagnetic immunity (EMI) has improved significantly.
Besides electromagnetic compatibility (EMC), another key feature of the TJA1040 is its
Standby mode. This mode provides a very low current consumption (less than 15 μA) and
remote wake-up capability via the CAN bus lines using a differential wake-up receiver.
This makes the TJA1040 the preferred transceiver for applications, which keep the
microcontroller and the applications VCC always active. Moreover the TJA1040 offers
ideal passive behavior when unpowered. It is completely invisible to the bus if the VCC
supply of the transceiver is switched off. This feature is of main interest for ignition key
controlled nodes (clamp-15), which are unpowered completely when the ignition key is
turned off while other ECUs continue communication (partial networking).
The TJA1040 is available without packaging (bare die) as well as in an SO8 package as
shown in Figure 1. It is pin compatible with other high speed CAN transceivers from NXP
Semiconductors like the C250, C251, TJA1050 and the TJA1041 Ref. 9 with the upper
part of its SO14 pinning.
TXD
1
GND
2
8
STB
7
CANH
TJA1040
VCC
3
6
CANL
RXD
4
5
SPLIT
Fig 1. Pinning diagram of the TJA1040
2. General high speed CAN application
Figure 2 illustrates a general high speed CAN application. Several ECUs (Electronic
Control Units) are connected via stubs to a linear bus topology. Each bus end is
terminated with 120 Ω (RT), resulting in the nominal 60 Ω bus load according to
ISO11898. The figure shows the split termination concept, which is helpful when
improving the EMC of high speed CAN bus systems Ref. 10. The former single 120 Ω
termination resistor is split into two resistors of half value (RT/2) with the center tap
connected to ground via the capacitor Cspl.
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TJA1040 high speed CAN transceiver
Voltage
Regulator
BAT
VCC
VCC
I/O
STB
CANH
TJA1040
CANL
RXD
μC
+
CAN
Sensor
Actuator
SPLIT
TXD
GND
ECU
ECU
ECU
RT/2
RT/2
RT/2
RT/2
Cspl
Cspl
Fig 2.
ECU
High speed CAN application
The block diagram in Figure 2 describes the internal structure of an ECU. Typically, an
ECU consists of a stand-alone transceiver (here TJA1040) and a host microcontroller with
integrated CAN-controller, which are supplied by a voltage regulator. While the high speed
CAN transceiver needs a +5 V supply voltage to support the ISO11898 bus levels, new
microcontroller products are increasingly using lower supply voltages like 3.3 V. In this
case a dedicated 3.3 V voltage regulator is necessary for the microcontroller supply. The
protocol controller is connected to the transceiver via a serial data output line (TXD) and a
serial data input line (RXD). The transceiver is attached to the bus lines via its two bus
terminals CANH and CANL, which provide differential receive and transmit capability. In
the case of the TJA1040 the pin STB is connected to an I/O pin of the host microcontroller
for operation mode control. The split termination approach can be further improved using
the pin SPLIT for DC stabilization of the common mode voltage Section 4.4.
The protocol controller outputs a serial transmit data stream to the TXD input of the
transceiver. An internal pull-up function within the TJA1040 sets the TXD input to logic
HIGH, which means that the bus output driver stays recessive in the case of a TXD open
circuit condition. In the recessive state (see Figure 3) the CANH and CANL pins are
biased to a voltage level of VCC/2. If a logic LOW level is applied to TXD, the output stage
is activated, generating a dominant state on the bus line (see Figure 3). The output driver
CANH provides a source output from VCC and the output driver CANL a sink output
towards GND. This is illustrated in Figure 4 showing the block diagram of the TJA1040.
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TJA1040 high speed CAN transceiver
If no bus node transmits a dominant bit, the bus stays in recessive state. If one or multiple
bus nodes transmit a dominant bit, then the bus lines enter the dominant state overriding
the recessive state (wired-AND characteristic).
The receiver converts the differential bus signal into a logic level signal, which is output at
RXD. The serial receive data stream is provided to the bus protocol controller for
decoding. The internal receiver comparator is always active. It monitors the bus while the
bus node is transmitting a message. This is required to support the non-destructive
bit-by-bit arbitration scheme of CAN.
Single Ended
Bus Voltage
3.6 V
2.5 V
1.4 V
CANH
CANL
Differential
Bus Voltage
5.0 V
Differential input voltage
range for dominant state
0.9 V
0.5 V
−1.0 V
time
Recessive Dominant
Recessive
Differential input voltage
range for recessive state
Fig 3. Nominal bus levels according to ISO11898
VCC
Time-Out &
Slope
TXD
Temperature
protection
V Split
SPLIT
CANH
VCC
CANL
STB
Wake-Up
Mode Control
RXD
Mux
Driver
Wake-Up
Filter
GND
Low Power
Receiver
Normal
Receiver
Fig 4. Block diagram of the TJA1040
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TJA1040 high speed CAN transceiver
3. Application specific requirements on high speed CAN
In-vehicle high speed CAN networks come with different requirements, depending on the
implemented application. First of all, high speed CAN is the ideal choice for all
applications which require a high data throughput (up to 1 Mbit/s). Though from the ECU
power management point of view, four different application areas (Type A - D) for high
speed CAN can be distinguished, as illustrated in Figure 5.
BAT
Clamp-30
VCC
Clamp-15
on/off
VCC
CTRL
μC
A
TXD
RXD
VCC
VCC
CTRL
μC
TRX
B
TXD
RXD
μC
TRX
TXD
RXD
μC
TRX
C
TXD
RXD
TRX
D
CANH
CANL
Fig 5. Different application areas for high speed CAN
Type A — Applications which have to be available all the time, even when the car is
parked and the ignition-key is off, are permanently supplied from a battery supply line,
called Clamp-30. However, those nodes need the possibility to reduce the current
consumption for saving the battery load by controlling the local ECU supply (VCC). These
type A applications make it possible to switch off the entire supply system of the ECU
including the microcontroller supply while keeping the wake-up capability via CAN.
Type B — Those nodes of applications, which need an always-active microcontroller, are
permanently supplied from the battery supply line Clamp-30 using a continuously active
VCC supply. To reduce the ECU power consumption, the transceiver needs to be set into a
mode with reduced supply current while VCC stays active.
Type C — Dedicated applications that need an always-active microcontroller and
therefore are permanently supplied from the Clamp-30 line. In contrast to type B
applications, further current can be saved, because the transceiver can become
completely unpowered by microcontroller control. These applications require absolute
passive bus behavior of the transceiver, while its voltage supply is inactive. This is needed
in order not to affect the remaining bus system, which might continue communication.
Type D — Applications, which do not need to be available with ignition-key off, are in that
case simply switched off and become totally unpowered. They are supplied from a
switched battery supply line, called Clamp-15. This supply line is only active with
ignition-key on. Depending on system requirements, e.g. partial communication of the still
supplied nodes during ignition-key off, these unpowered nodes need to behave passively
towards the remaining bus, similar to type C applications.
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TJA1040 high speed CAN transceiver
The NXP Semiconductors transceiver products TJA1040, TJA1041 and TJA1050 (see
also Section 10.1) offer different features to completely cover the described power
management requirements.
3.1 Type A applications
The TJA1041 can be put into a Sleep mode (all VCC supplies off), which allows reducing
the total current consumption of the entire ECU to typically 20 μA, while keeping the
capability to receive wake-up events from the bus and to restart the application. The
TJA1041 can take control over the ECU internal power supply and wake-up requests. It is
the first choice transceiver for applications of type A, which need to be remotely available
all the time.
3.2 Type B applications
Type B applications require a dedicated transceiver operation mode with reduced current
consumption, while VCC stays active all the time. The TJA1040 with its Standby mode
offers the best choice for these applications. During Standby mode the device reduces the
VCC supply current to a minimum in order to save current. In spite of the very low current
consumption, the TJA1040 still monitors the CAN bus lines for bus traffic and allows
waking up the host microcontroller.
3.3 Type C and D applications
Within these applications, the supply voltage of the transceiver is directly controlled by the
host microcontroller or the ignition key. The transceiver does not necessarily need to
provide a dedicated mode with reduced power consumption. Most important is a passive
behavior of the transceiver, when unpowered. Parasitic currents within the ECU towards
the microcontroller as well as towards the bus lines have to be avoided. Depending on the
systems CAN bus requirements, the TJA1040 as well as the TJA1050 support this kind of
application.
If there is further bus communication of other CAN ECUs present, while the type C
application transceiver is switched off (partial networking), the TJA1040 is the first choice.
This is because of the perfect floating behavior on the bus lines while VCC is off. The
remaining bus system will not be affected by any unpowered TJA1040.
If there is no ongoing communication (no partial networking), the TJA1050 offers a
comparable alternative. In contrast to the TJA1040, the unpowered TJA1050 affects a
running bus communication due to a small reverse bus current. This slightly increases the
electromagnetic emission during partial networking time. But if there is no ongoing
communication, the TJA1050 achieves the same performance as the TJA1040.
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TJA1040 high speed CAN transceiver
Type A
Type B
Type C/D
ECU
ECU
ECU
ECU
1041
1040
1040
1050
Fig 6. Application areas for the TJA1040, TJA1041 and TJA1050
4. Main features of the TJA1040
4.1 Operation modes
The TJA1040 provides two different operation modes: Normal mode and Standby mode.
Similar to the C250 and C251 transceivers, a dedicated pin selects the actual operation
mode.
4.1.1 Normal mode
During normal CAN communication, the Normal mode is selected by applying a LOW
level to the pin STB. In this mode the transceiver can transmit and receive data via the
bus lines CANH and CANL. The digital bit stream input at TXD is converted into the
corresponding analog bus signals. Simultaneously, the Normal Receiver (see Figure 4)
converts the analog data on the bus lines into a digital bit stream, which is output to RXD
via the internal multiplexer. In Normal mode the bus lines are biased to VCC/2 and the
transmitter is enabled.
4.1.2 Standby mode
The Standby mode with significantly reduced current consumption is activated with a
HIGH level applied to pin STB. In Standby mode the transmitter and receiver of the
TJA1040 are switched off and therefore are not capable of transmitting and receiving
regular CAN messages. However, a Low Power Receiver (see Figure 4) monitors the bus
lines for CAN messages. Only dominant CAN states, which are stable longer than the bus
wake-up time tBUS Ref. 1, and therefore indicate bus traffic, are reflected to the pin RXD
by a logic LOW level (wake-up detected). This offers a maximum electromagnetic
immunity against unwanted wake-up events. To enter the Normal mode after the wake-up
detection a LOW level has to be applied to the pin STB. Entering Normal mode activates
the Normal Receiver of the TJA1040 again.
Table 1.
Operation modes of the TJA1040
Operation mode
STB
Bus Bias
RXD = LOW
RXD = HIGH
Bus recessive
Normal
LOW
VCC/2
Bus dominant
Standby
HIGH
Ground
Wake-up detected No wake-up
detected
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4.2 Excellent EMC behavior
Electromagnetic compatibility has been one main design target of the TJA1040. During
Normal mode a precondition for a low electromagnetic emission in the critical AM-band is
a very good symmetry of the signals CANH and CANL, when switching between the
dominant and recessive levels and vice versa. In the TJA1040 design, this symmetry is
optimised by using a fixed slope function instead of a variable one, known from the
C250/C251. Based on the fixed and optimised slope time, the emission could be
decreased by more than 20 dB compared to the C250/C251, especially if the split
termination approach is used. If a specific system implementation needs further reduction
of the emission and enhancement of immunity in the FM-band, it is possible to add a
common mode choke externally to the bus pins CANH and CANL.
4.3 Passive behavior
In up to date in-vehicle networks partial networking is widely implemented. In Section 3
partial networking is introduced with different applications. In these typical example
applications, some transceivers can become unpowered (e.g. Clamp-15 nodes) while
other transceivers are continuously supplied (e.g. Clamp-30 nodes). In such networks the
TJA1040 is favoured for those applications, which are partly unpowered, because of its
excellent passive behavior to the bus when the VCC supply is switched off. In addition, the
TJA1040 is protected against reverse currents via the pins TXD, RXD and STB. There will
be no backward current via those pins if the accompanying microcontroller is still supplied.
4.4 Common mode stabilization, SPLIT pin
The high impedance characteristic of the bus during recessive state leaves the bus
vulnerable to even small leakage currents, which may occur with unpowered transceivers
or ECUs within the bus system. As a result the common mode voltage can show a
significant voltage drop from the nominal VCC/2 value. After transmitting the first dominant
bit of a CAN frame (Start-of-Frame Bit) the common mode voltage would restore to its
nominal value. This would lead to a large common mode step and an increased emission.
The TJA1040 provides a common mode stabilization by offering a voltage source of
nominal VCC/2 at the pin SPLIT (Figure 7). The common mode stabilization improves the
EMC performance of the TJA1040 significantly. Its use is recommended if there are
unpowered nodes while other nodes keep communicating.
CANH
RT/2
TJA1040
SPLIT
CG
RT/2
CANL
Fig 7. Common mode stabilization with SPLIT pin
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TJA1040 high speed CAN transceiver
4.5 Interfacing to microcontroller with non 5V supply
As the TJA1040 supports the physical layer of the ISO11898 standard, it requires a +5 V
supply voltage as reference voltage. On the other hand, new microcontroller generations
often require supply voltages lower than 5 V, mostly +3.3 V and less.
In order to support a microcontroller with low supply voltages, the TJA1040 provides a
reduced input threshold voltage at its input pins TXD and STB. An input voltage of 2 V at
these pins is safely interpreted as a HIGH level and allows a direct drive out of a 3 V
microcontroller. It should be noticed that the output level of the TJA1040's pins towards
the microcontroller is still based on the 5 V transceiver supply. TXD and STB provide an
internal weak pull-up current source towards VCC (fail-safe open circuit behavior) while
RXD offers a push-pull driver stage, which drives the pin to VCC in a recessive bus state.
Common 3 V microcontrollers tolerate voltages above their own supply voltage if the
current is limited. Due to the weak and current limited pull-up source within TXD and STB,
a direct connection between the 3 V microcontroller and the 5 V supplied TJA1040 is
typically possible without further protection measures (please check the data sheet of the
chosen microcontroller). Since RXD offers a strong driver towards VCC, the RXD input of
the microcontroller needs to be 5 V-tolerant. Alternatively a level shifter or a simple series
resistor between RXD of the TJA1040 and the microcontroller could be used.
Take into account that any hardware between the transceiver's TXD/RXD interface and
the microcontroller might lengthen the loop delay of the system, which has an impact on
the overall bit timing parameters. Especially at very high bit rates ≥ 500 kBit/s, this
parameter has to be checked carefully.
4.6 TXD dominant time-out function
The TJA1040 provides a TXD dominant time-out function, which prevents the bus lines
from being clamped to a permanent dominant level and from blocking all network
communication.
The function of the TXD dominant time-out is illustrated in Figure 8. After a maximum
allowable TXD dominant time (tDOM) the transmitter of the transceiver is disabled and
releases the bus lines recessive again. The next dominant output drive is possible only
after setting TXD to HIGH again. According to the CAN protocol a maximum of eleven
successive dominant bits is allowed on TXD only (worst case of five successive dominant
bits followed immediately by an error frame). Along with the minimum specified TXD
dominant time-out (tDOM_ min), this limits the minimum suitable bit rate to 40 kbit/s.
tDOM
TXD
transmitter
enabled
recessive
dominant
transmitter
disabled
CANH
BUS
VDiff
CANL
time
Fig 8. TXD dominant time-out feature
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TJA1040 high speed CAN transceiver
5. Hardware application
Besides the excellent behavior of the TJA1040 itself, a careful system implementation
dealing with termination, topology and external circuitry is very important to make
optimum use of the transceiver’s advantages. This chapter presents a typical application
example for the TJA1040 and application hints dealing with the split termination concept
and required external circuitry.
Figure 9 shows how to integrate the TJA1040 within a typical application. In the example,
a 5 V supplied host microcontroller is assumed. A dedicated 5 V regulator supplies the
TJA1040 transceiver and the microcontroller. Two capacitors are placed at the output of
the voltage regulator for VCC supply buffering purposes. The CAN-controller of the
microcontroller is connected to the transceiver via TXD and RXD. Pin STB is connected to
an I/O pin of the host microcontroller for operation mode control. The CAN bus lines are
attached via the two bus terminals CANH and CANL. In-between matching capacitors are
placed and a typical split termination is shown to improve EMC performance.
BAT
5V
*
100 nF
CANH
VCC
<100pF
60 (1k3)**
optional ***
CAN
bus
SPLIT
VCC
TXD
TXD
RXD
RXD
μC
+
CAN
TJA1040
e.g. 47nF
STB
60 (1k3)**
I/O
CANL
GND
GND
<100pF
Size of capacitor depends on regulator.
*
** For stub nodes an optional "weak" termination improves the EMC behaviour of the system in terms of emission.
*** Optional common mode stabilization by a voltage source of VCC/2 at the pin SPLIT.
Fig 9. Typical application for the TJA1040 with a 5V microcontroller
5.1 Split termination concept
Practice has shown that effective reduction of electromagnetic emission can be achieved
by a modified bus termination concept called split termination. In addition this concept
contributes to higher immunity of the bus system. The split termination concept is
illustrated in Figure 10. Basically each of the two termination resistors of the bus line end
nodes is split into two resistors of equal value, i.e. two 60 Ω resistors instead of one 120 Ω
resistor. It is common practice to include the termination within the ECU. Stub nodes,
which are connected to the bus via stubs, can optionally be equipped with a similar split
termination configuration. The resistor value for the stub nodes has to be chosen such
that the busload of all the termination resistors stays within the range of 45 Ω to 65 Ω. As
an example for up to 10 nodes (8 stub nodes and 2 bus line end nodes) a typical resistor
value is 1.3 kΩ.
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Split termination for
stub node (optional)
1.3k
Split termination for
stub node (optional)
1.3k
1.3k
CG
CG
Split termination for
bus line end node
60
1.3k
Split termination for
bus line end node
CANH
60
Bus Line
CANL
CG
60
60
CG
Fig 10. Typical split termination concept
5.2 Optional circuitry at CANH and CANL
The EMC performance of the TJA1040 has been optimized for use of the split termination
without a choke. Hence, it is highly recommended to implement the split termination. The
excellent output stage symmetry allows going without chokes as shown by different
emission measurements. If, however, the system performance is still not sufficient, there
is the option to use additional measures like common mode chokes, capacitors and ESD
clamping diodes.
5.2.1 Common mode choke
A common mode choke provides high impedance for common mode signals and low
impedance for differential signals. Due to this, common mode signals produced by RF
noise and/or by non-perfect transceiver driver symmetry get effectively reduced while
passing the choke. In fact, a common mode choke helps to reduce emission and to
improve immunity against common mode disturbances.
Former transceiver devices usually needed a common mode choke to fulfil the stringent
emission and immunity requirements of the automotive industry when using unshielded
twisted-pair cable. The TJA1040 has the potential to build in-vehicle bus systems without
chokes. Whether a choke is needed or not finally depends on the specific system
implementation like the wiring harness and the symmetry of the two bus lines (matching
tolerances of resistors and capacitors).
Besides the RF noise reduction the stray inductance (non-coupled portion of inductance)
may establish a resonant circuit together with pin capacitance. This can result in
unwanted oscillations between the bus pins and the choke, both for differential and
common mode signals, and in extra emission around the resonant frequency. To avoid
such oscillations, it is highly recommended to use only chokes with a stray inductance
lower than 500 nH. Bifilar wound chokes typically show an even lower stray inductance.
Figure 11 shows an application, using a common mode choke. As shown the choke shall
be placed nearest to the transceiver bus pins.
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SPLIT
0Ω
CANH
RT/2
CAN
bus
TJA1040
RT/2
CSPLIT
CANL
CH
Split
Common
Capacitors
Mode Choke Termination (Optional)
(i.e. B82789-C104)
CL
ESD protection diodes
(e.g. NXP PESD1CAN)
Fig 11. Optional circuitry at CANH and CANL
5.2.2 Capacitors
Matching capacitors (in pairs) at CANH and CANL to GND (CH and CL) are frequently
used to enhance immunity against electromagnetic interferences. Along with the
impedance of corresponding noise sources (RF), capacitors at CANH and CANL to GND
form an RC low-pass filter. Regarding immunity, the capacitor value should be as large as
possible to achieve a low corner frequency. The overall capacitive load and impedance of
the output stage establish an RC low-pass filter for the data signals. The associated
corner frequency must be well above the data transmission frequency. This results in a
limit for the capacitor value depending on the number of nodes and the data transmission
frequency. Notice that capacitors increase the signal loop delay due to reducing rise and
fall times. Due to that, bit timing requirements, especially at 500 kbit/s, call for a value of
lower than 100 pF (see also SAE J2284 and ISO11898). At a bit rate of 125 kbit/s the
capacitor value should not exceed 470 pF. Typically, the capacitors are placed between
the common mode choke (if applied at all) and the ESD clamping diodes as shown in
Figure 11.
5.2.3 ESD protection
The TJA1040 is designed to withstand ESD pulses of up to 6 kV according to the human
body model at the bus pins CANH, CANL and pin SPLIT and thus typically does not need
further external protection methods. Nevertheless, if much higher protection is required,
external clamping devices can be applied to the CANH and CANL lines.
NXP offers a dedicated protection device for the CAN bus, providing high robustness
against ESD and automotive transients. The PESD1CAN ESD protection diode Ref. 13,
featuring a very fast diode structure with very low capacitance (typ. 11 pF), is compliant to
IEC61000-4-2 (level 4), thus allowing air and contact discharge of more than 15 kV and
8 kV, respectively. Tests at an independent test house have confirmed typically more than
20 kV ESD robustness for ECUs equipped with the PESD1CAN diode and a common
mode choke. To be most effective the PESD1CAN diode shall be placed close to the ECU
connector as shown in Figure 11.
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5.3 Buffering at VCC
The voltage supply via the pin VCC provides the current needed for the transmitter and
receiver of the TJA1040. The voltage regulator for the supply must be able to deliver a
current of 71 mA on average. Using a linear voltage regulator, it is recommended to
stabilize the output voltage with a bypass capacitor of about 22 μF. As illustrated in
Figure 9 this capacitor should be connected at the output of the voltage regulator.
An additional capacitor in the range 47 nF to 100 nF should be connected between VCC
and GND close to the transceiver. Its function is to buffer the VCC supply voltage. For
reliability reasons it might be useful to apply two capacitors in series connection between
VCC and GND. Thus, a single shorted capacitor cannot short-circuit the VCC supply.
5.4 Optional circuitry at TXD and RXD
Depending on the used microcontroller and PCB layout, the digital signals at TXD and
RXD during bit transitions might degrade the system EMC performance. Here a series
resistor of about 1 kΩ within the TXD and/or RXD line could be an option to reduce the
electromagnetic emission of the system. Along with the pin capacitance this would help to
smooth the edges to some degree. For high bus speeds (≥ 500 kbit/s) the additional delay
within TXD and RXD has to be taken into account.
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6. Pin FMEA
This chapter provides an FMEA (Failure mode and Effects Analysis) for typical failure
situations, when dedicated pins of the TJA1040 are short-circuited to supply voltages like
VBAT, VCC, GND or to neighbored pins or are simply left open. The individual failures are
classified, due to their corresponding effects on the transceiver and bus communication in
Table 2.
Table 2.
Classification of failure effects
Class
Effects
A
Damage to transceiver
Bus may be affected
B
No damage to transceiver
No bus communication possible
C
No damage to transceiver
Bus communication possible
Corrupted node not able to communicate
D
No damage to transceiver
Bus communication possible
Reduced functionality of transceiver
Table 3, Table 4 and Table 5 show the FMEA matrix with the failure classifications and
additional remarks on failure effects:
Table 3.
Pin
(1) TXD
FMEA matrix for pin short-circuits between neighbored pins
Short to VBAT (12V … 40V)
Short to VCC (5V)
Class Remark
Class
Remark
A
Limiting value exceeded
C
TXD clamped recessive; node
eventually goes Bus-Off
(2) GND
C
Node is left unpowered
C
Transceiver is left unpowered
(3) VCC
A
Limiting value exceeded
---
---
(4) RXD
A
Limiting value exceeded
C
RXD is clamped recessive and
CAN controller expects an idle
bus; node produces Error
Frames on bus until Bus-Off is
entered; communication
continuously disturbed due to
random communication trials of
shorted node
(5) SPLIT
D
Bus charged to VBAT - level; bit
timing problem possible
D
Bus charged to VCC - level; bit
timing problem possible
(6) CANL
B
No bus communication
B
No bus communication
(7) CANH
D
Degradation of EMC; bit timing
problem possible
D
Degradation of EMC; bit timing
problem possible
(8) STB
A
Limiting value exceeded
C
Transceiver permanent in
Standby mode (transmitter
disabled)
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Table 4.
FMEA matrix for pin short-circuits to GND and open pins
Pin
Short to ground
Open
Class Remark
Class
Remark
(1) TXD
C
TXD dominant clamping;
transmitter disabled; node
eventually goes Bus-Off
C
TXD clamped recessive; node
eventually goes Bus-Off
(2) GND
---
---
C
Transceiver is left unpowered
and behaves passive to the bus
lines
(3) VCC
C
Transceiver is left unpowered
C
and behaves passive to the bus
lines
Transceiver is left unpowered; no
VCC reverse supply from mC to
transceiver
(4) RXD
C
RXD clamped dominant
C
Node may produce Error Frames
on bus until Bus-Off is entered
(5) SPLIT
D
Bus discharged to GND - level;
bit timing problem possible
D
No DC common mode
stabilization
(6) CANL
D
Degradation of EMC; bit timing
problem possible
C
Receiving from bus possible only,
if there is no termination resistor
within this interrupted bus
segment present; transmitting
across the interruption is not
possible
(7) CANH
B
No bus communication
C
Receiving from bus possible only,
if there is no termination resistor
within this interrupted bus
segment present; transmitting
across the interruption is not
possible
(8) STB
D
Transceiver permanent in
Normal mode
C
Transceiver permanent in
Standby mode (transmitter
disabled)
Table 5.
FMEA matrix for pin short-circuits between neighbored pins
Pin short
Short to neighboured pin
Class Remark
TXD-GND
C
Transmitter disabled after TXD Dominant Timeout
GND-VCC
C
TRX unpowered, bus not affected
VCC-RXD
C
RXD is clamped recessive, bus communication disturbed
SPLIT-CANL
D
Degradation of EMC
CANL-CANH
B
No bus communication, bus clamped recessive
CANH-STB
D
Transceiver is not able to enter Standby mode if the bus is driven
dominant
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7. Bus network aspects
This chapter deals with items like the maximum number of nodes, the maximum bus line
length and topology aspects. In particular the topology appears to have a significant
influence on the system performance.
7.1 Maximum number of nodes
The number of nodes which can be connected to a bus depends on the minimum load
resistance a transceiver can drive. The TJA1040 transceiver provides an output drive
capability down to a minimum load of RL,min = 45 Ω for VCC > 4.75 V. The overall busload
is defined by the termination resistance RT, the bus line resistance RW and the
transceiver's differential input resistance Rdiff. The DC circuit model of a bus system is
shown in Figure 12. For worst case consideration the bus line resistance RW is considered
to be zero. This leads to the following relations for calculating the maximum number of
nodes:
R T.min × R diff.min
----------------------------------------------------------- > R L.min
n max × R T.min + 2R diff.min
(1)
Rearranged to nmax :
2
1
n max < R diff.min × ⎛ -------------- – --------------⎞
⎝R
⎠
L.min R T.min
output of
transmitting node
(2)
bus wiring
RW
node inputs
input of
receiving node
CANH
termination
RT
termination
Rdiff
DC
+
-
Rdiff
Vdiff out
RW
n-2
Rdiff
Vdiff in
RT
CANL
Node 1
Node 2...n-1
Node n
Fig 12. DC circuit model for a bus system according to ISO11898
Table 6 gives the maximum number of nodes for two different termination resistances.
Notice that connecting a large number of nodes requires relatively large termination
resistances.
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Table 6.
Maximum number of nodes (see datasheets for Rdiff, min and RL,min)
Transceiver
Rdiff,min(kΩ)
RL,min(Ω)
Nodes
(maximum)
Nodes
(maximum)
(RT,min=118 Ω)
(RT,min=130 Ω)
TJA1040
TJA1041
TJA1050
25
45 @ VCC=4.75 V 131
170
C250
C251
20
45 @ VCC=4.9 V
136
105
7.2 Maximum bus line length
The maximum achievable bus line length in a CAN network is determined essentially by
the following physical effects:
1. Loop delays of the connected bus nodes (CAN controller, transceiver etc.) and the
delay of the bus line.
2. Relative oscillator tolerance between nodes.
3. Signal amplitude drop due to the series resistance of the bus cable and the input
resistance of bus nodes (for a detailed description refer to Ref. 11).
Effects 1 and 2 result in a value for the maximum bus line length with respect to the CAN
bit timing Ref. 11. Effect 3, on the other hand, results in a value with respect to the output
signal drop along the bus line. The minimum of the two values has to be taken as the
actual maximum allowable bus line length. As the signal drop is only significant for very
long lengths, effect 3 can often be neglected for high data rates.
Table 7.
Maximum bus line length for some standards and the TJA1040 (BT tol. = Bit Time
Tolerance)
Specification
Data rate
125 kbit/s
(BT tol. = +/- 1.25%)
250 kbit/s
(BT tol. = +/- 0.75%)
500 kbit/s
(BT tol. = +/- 0.5%)
SAE J2284
50 m
50 m
30 m
TJA1040
80 m
80 m
40 m
Table 7 gives the maximum bus line length for the bit rates 125 kbit/s, 250 kbit/s and
500 kbit/s, along with values specified in the SAE J2284 Ref. 5 standard associated to
CAN. The calculation is based on effects 1 and 2 assuming a minimum propagation delay
between any two nodes of 200 ns and a maximum bus signal delay of 8 ns/m. Notice that
the stated values apply only for a well-terminated linear topology. Bad signal quality
because of inadequate termination can lower the maximum allowable bus line length.
7.3 Topology aspects
The topology describes the wiring harness structure. Typical structures are linear, star- or
multistar-like. In automotive, shielded or unshielded twisted pair cable usually functions as
a transmission line. Transmission lines are generally characterized by the length-related
resistance RLength, the specific line delay tdelay and the characteristic line impedance Z.
Table 8 shows the physical media parameters specified in the ISO11898 and SAE J2284
standard. Notice that SAE J2284 specifies the twist rate rtwist in addition.
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Table 8.
Physical media parameters of a pair of wires (shielded or unshielded)
Parameter
Notation
Unit
ISO 11898
SAE J2284
Min.
Nom.
Max.
Min.
Nom.
Max.
Impedance
Z
Ω
95
120
140
108
120
132
Length-related
resistance
RLength
mΩ/m
-
70
-
-
70
-
Specific line delay tdelay
ns/m
-
5
-
-
5.5
-
Twist rate
twist/m
-
-
-
33
-
50
rtwist
7.3.1 Ringing due to signal reflections
Transmission lines must be terminated with the characteristic line impedance, otherwise
signal reflections will occur on the bus causing significant ringing. The topology has to be
chosen such that reflections will be minimized. Often the topology is a trade-off between
reflections and wiring constraints.
CAN is well prepared to deal with reflection ringing due to some useful protocol features:
• Only recessive to dominant transitions are used for resynchronization.
• Resynchronization is allowed only once between the sample points of two bits and
only, if the previous bit was sampled and processed with recessive value.
• The sample point is programmable to be close to the end of the bit time.
7.3.2 Linear topology
The high speed CAN standard ISO11898 defines a single line structure as network
topology. The bus line is terminated at both ends with a single termination resistor. The
nodes are connected via unterminated drop cables or stubs to the bus. To keep the
ringing duration short compared to the bit time, the stub length should be as short as
possible. For example the ISO11898 standard limits the stub length to 0.3 m at 1 Mbit/s.
The corresponding SAE standard, J2284-500, recommends keeping the stub length
below 1 m. To minimize standing waves, ECUs should not be placed equally spaced on
the network and cable tail lengths should not all be the same Ref. 5. Table 9 along with
Figure 13 illustrate the topology requirements of the SAE J2284-500 standard. At lower bit
rates the maximum distance between any two ECUs as well as the ECU cable stub
lengths may become longer.
Off Board to
ECU n-2
ECU 2
ECU 3
L3
ECU n-1
DLC
L1
termination
ECU 1
d
L2
trunk cable
termination
ECU n
Fig 13. Topology requirements of SAE J2284
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In practice some deviation from that stringent topology proposals might be necessary,
because longer stub lengths are needed. Essentially the maximum allowable stub length
depends on the bit timing parameters, the trunk cable length and the accumulated drop
cable length. For a rule of thumb calculation of the maximum allowable stub length refer to
Ref. 12.
The star topology is neither covered by ISO11898 nor by SAE J2284. However, it is
sometimes used in automotive applications to overcome wiring constraints within the car.
Generally, the signal integrity suffers from a star topology compared to a linear topology. It
is recommended to prove the feasibility of a specific topology in each case by simulations
or measurements on a system setup.
Table 9.
ECU topology requirements of SAE J2284-500
Parameter
Symbol
Unit
Min.
Nom.
Max.
ECU cable stub length
L1
m
0
-
1
In-vehicle DLC cable stub length
L2
m
0
-
1
Off board DLC cable stub length
L3
m
0
-
5
Distance between any two ECUs
d
m
0.1
-
30
8. Interoperability
Interoperability of the high speed CAN transceivers C250, C251, TJA1040, TJA1041 and
TJA1050 (see also Section 10.1) is guaranteed due to their compatibility with the
ISO11898 standard. They can work together in the same bus network.
There are some issues related to different bus biasing behavior during low-power
operation, which are considered in this chapter. Table 10 shows the bus biasing in the
different operation modes as well as in unpowered condition. Whenever there is a
difference in the bus biasing, a steady DC compensation current will flow within the
system. The common mode input resistance mainly defines the amount of this
compensation current. This is shown in Figure 14 for a bus in recessive state including
TJA1040 and TJA1041 nodes.
Table 10.
Bus biasing of NXP transceivers depending on operation mode
Transceiver
Operation mode
Bus bias
TJA1040
Normal
VCC/2
TJA1041
TJA1050
C250/C251
Standby
weak GND
Unpowered
floating
Normal, Pwon/Listen-Only
VCC/2
Standby, Sleep, Go-to-Sleep,
Unpowered
weak GND
Normal, Silent
VCC/2
Unpowered
weak GND
Normal, Standby
VCC/2
Unpowered
GND
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Powered TJA1040 nodes
TJA1041 nodes in Sleep or Standby
RCM(TJA1040)/nTJA1040
RCM(TJA1041)/nTJA1041
CANH
Icomp
CANL
VCC/2
RCM(TJA1040)/nTJA1040
RCM(TJA1041)/nTJA1041
VCC/2
Fig 14. Equivalent bus circuit for a mixed system of TJA1040 nodes in Normal mode and
TJA1041 nodes in Standby/Sleep mode
Due to the large common mode input resistance, CAN communication is not affected
when parts of the network are still within low-power mode, while other nodes have already
started communication. However, degradation of the emission performance is expected.
The following formula allows calculation of the whole biasing compensation current in a
mixed system of TJA1040 and TJA1041 nodes.
V CC ⁄ 2
I comp,max = ----------------------------------------------------------------------------------------------------------------------------R CM ( TJA1040 ) ⁄ 2n TJA1040 + R CM ( TJA1041 ) ⁄ 2n TJA1041
(3)
Where:
nTJA1040 : number of nodes of powered TJA1040
nTJA1041 : number of nodes of TJA1041 in Standby/Sleep mode
RCM(TJA1040) =15k: min. common mode input resistance of TJA1040 at pin CANH/L
RCM(TJA1041) =15k: min. common mode input resistance of TJA1041 at pin CANH/L
Table 11.
Conditions leading to DC compensation current
Transceiver
TJA1041
TJA1050
C250/C251
TJA1040
Normal
Standby
Unpowered
Normal
---
X
---
Pwon/Listen-Only
---
X
---
Standby
X
---
---
Sleep
X
---
---
Goto-Sleep
X
---
---
Unpowered
X
---
---
Normal
---
X
---
Silent
---
X
---
Unpowered
X
---
---
Normal
---
X
---
Standby
---
X
---
Unpowered
X
---
---
X = DC compensation current --- = No DC compensation current
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Table 11 identifies the conditions leading to different bus biasing and DC compensation
current when different high speed CAN transceivers work together in the same bus
network. The perfect passive behavior of the TJA1040 when unpowered is clear
recognisable in Table 11 since an unpowered TJA1040 node never leads to a DC
compensation current.
8.1 TJA1040 mixed with TJA1041 nodes
In a mixed system of TJA1040 and TJA1041 nodes, it is not expected to have situations of
different bus biasing. In the low-power modes both the TJA1040 and TJA1041 show a
weak termination to GND. When the bus is in power-down with all nodes either in Standby
or Sleep mode, there is no DC compensation current. During normal CAN operation,
when all nodes are in Normal (high speed) or Pwon/Listen-Only mode for diagnosis
features, the bus is collectively biased to VCC/2. There is no DC compensation current.
8.2 TJA1040 mixed with TJA1050 or C250/C251 nodes
Table 11 reveals also that some compensation current is flowing if TJA1040 nodes are in
Normal mode, while other TJA1050 or C250/C251 nodes are left unpowered. Moreover,
compensation current occurs when TJA1040 nodes are in Standby mode, while other
TJA1050 or C250/C251 nodes are kept powered in any operation mode. However, the
compensation current is negligible compared to the current saving due to the very low
standby supply current of the TJA1040. So, upgrading existing C250/C251 ECUs with the
TJA1040 always improves the overall current budget of the system, even if there are
some C250/C251 nodes left in the vehicle.
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9. Upgrading hints
This chapter describes all items to be taken into account, when an existing application
using the C250/C251 transceivers should be upgraded towards the TJA1040. In Figure 15
and Figure 16 typical application circuits for the C250/C251 and TJA1040, respectively,
are shown.
VCC
Supply
VCC
VCC
CANH
<100pF
60 (1k3) *
CAN
bus
Vref
TxD
TxD
RxD
RxD
μC
+
CAN
C250/C251
RS
e.g. 47nF
Rs
60 (1k3) *
I/O
CANL
GND
GND
<100pF
*
For stub nodes an optional "weak" termination improves the EMC behaviour of the system in terms of emission.
Fig 15. Typical application circuit for the C250/C251
VCC
supply
CANH
VCC
<100pF
60 (1k3) *
optional **
CAN
bus
SPLIT
VCC
TXD
TXD
RXD
RXD
μC
+
CAN
TJA1040
e.g. 47nF
STB
60 (1k3) *
I/O
CANL
GND
GND
<100pF
*
**
For stub nodes an optional "weak" termination improves the EMC behaviour of the system in terms of emission.
Optional common mode stabilization by a voltage source of VCC/2 at the pin SPLIT.
Fig 16. Typical application circuit for the TJA1040
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9.1 Hardware check list C250/C251 → TJA1040
Comparing the application circuits in Figure 15 and Figure 16, the following items have to
be checked when replacing the C250/C251 by the TJA1040:
• If the pin SPLIT should be used for DC stabilization of the common mode voltage, the
pin SPLIT (corresponds to pin Vref of C250/C251) is connected optionally to the
center tap of the split termination. The pin SPLIT can simply be left open, if not used.
• If the mode control pin 8 of the C250/C251 was applied with a slope control resistor
RS for slope control, this resistor has to be removed. The corresponding pin of the
TJA1040 (pin STB) should be directly connected to an output port of the
microcontroller. There is the same polarity vs. function of this signal and, no need for a
software modification.
• The TJA1040 does not necessarily need a common mode choke. The split
termination is highly recommended as it ensures lowest emission, especially in the
AM-band.
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10. Appendix
10.1 Comparison of C250/C251, TJA1040, TJA1041 and TJA1050
Table 12 lists the main differences between the C250/C251, TJA1040, TJA1041 and
TJA1050 from an application point of view.
Table 12.
Main differences between C250/C251, TJA1040, TJA1041 and TJA1050
Feature
C250
C251
TJA1040
TJA1041
TJA1050
VCC voltage range
4.5 - 5.5 V
4.5 - 5.5 V
4.75 - 5.25 V
4.75 - 5.25 V
4.75 - 5.25 V
Max. DC voltage at bus
pins
−8V…+18 V
−36 V…+36 V
−27V…+40 V
−27V…+40 V
−27V…+40 V
Loop Delay
(RS=0) 190 ns
(RS=24k) 320 ns
(RS=0) 190 ns
255 ns
255 ns
250 ns
Standby mode current
consumption (remote
wake-up)
< 170 μA
< 275 μA
< 15 μA
< 10 μA at VCC
< 30 μA at BAT
Not
supported
Sleep mode current
consumption (remote
wake-up)
Not
supported
Not
supported
Not
supported
< 30 μA at BAT
Not
supported
Slope Control
Variable
Variable
Fixed, EMC
optimized
Fixed, EMC
optimized
Fixed, EMC
optimized
Passive behavior
(Leakage current of bus
pins; VCC=0 V)
< 1000 μA
(VCANH/L=7 V)
< 2000 μA
(VCANH/L=7 V)
0 μA
(VCANH/L=5 V)
< 250 μA
(VCANH/L=5 V)
< 250 μA
(VCANH/L=5 V)
Common mode
stabilization (SPLIT Pin)
No
No
Yes
Yes
No
Bus failure diagnosis
No
No
No
Yes
No
System Fail-Safe Features No
No
TXD time-out;
no reverse
currents
TXD time-out;
RXD clamping;
VCC clamping; no
reverse currents
TXD time-out;
no reverse
currents
3V Microcontroller support No
No
Yes, 5 V tolerant
RXD input at μC
needed
Yes
Yes, 5 V tolerant
RXD input at μC
needed
Power-on detection
(first battery connection)
No
No
Yes
No
No
Figure 17 shows the pinning of the C250/C251, TJA1040, TJA1041 and TJA1050. Apart
from renaming two pins the pinning of the SO8 package transceivers is identical.
Accordingly the upper part of the SO14 pinning of the TJA1041 is compatible to the SO8
pinning of the other transceiver products.
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TXD
1
GND
2
8
Rs
TXD
1
7
CANH
GND
2
C250/251
8
STB
7
CANH
TJA1040
VCC
3
6
CANL
VCC
3
6
CANL
RXD
4
5
Vref
RXD
4
5
SPLIT
TXD
1
8
S
TXD
1
14
NSTB
GND
2
7
CANH
GND
2
13
CANH
VCC
3
12
CANL
RXD
4
11
SPLIT
VI/O
5
10
VBAT
EN
6
9
WAKE
INH
7
8
ERR
TJA1050
VCC
3
6
CANL
RXD
4
5
VREF
SO8-type
CAN-Xeiver
TJA1041
Fig 17. Pinning of the C250/C251, TJA1040, TJA1050 and TJA1041
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11. Abbreviations
Table 13.
Abbreviations
Acronym
Description
CAN
Controller Area Network
Clamp-15
ECU architecture, Battery supply line after the ignition key, module is
temporarily supplied by the battery only (ignition key on)
Clamp-30
ECU architecture, direct battery supply line before the ignition key, module is
permanently supplied by the battery
ECU
Electronic Control Unit
EMC
Electromagnetic Compatibility
EME
Electromagnetic Emission
EMI
Electromagnetic Immunity
FMEA
Failure Mode and Effects Analysis
SOI
Silicon On Insulator
12. References
[1]
Data Sheet TJA1040, High-Speed CAN transceiver — Philips Semiconductors,
2003 Oct 14
[2]
Road Vehicles - Interchange of Digital Information - Controller Area Network
(CAN) for high-speed communication — ISO11898, 1993
[3]
Road Vehicles - Controller Area Network (CAN) - Part 2: High-speed medium
access unit — ISO11898-2, DIS 2002
[4]
Road Vehicles - Controller Area Network (CAN) - Part 5: High-speed medium
access unit with low power mode — ISO11898-5, DIS 2006
[5]
High Speed CAN (HSC) for Vehicle Applications at 500kbps — SAE J2284,
1999
[6]
Data Sheet TJA1050, High Speed CAN transceiver — Philips Semiconductors,
2003 Oct 22
[7]
Data Sheet PCA82C250, CAN controller interface — Philips Semiconductors,
2000 Jan 13
[8]
Data Sheet PCA82C251, CAN controller interface — Philips Semiconductors,
2000 Jan 13
[9]
Data Sheet TJA1041, High-Speed CAN transceiver — Philips Semiconductors,
2003 Oct 14
[10] SAE Conference Paper 950298, EMC Measures for Class C Communication
Systems using Unshielded Cable — Lütjens/Eisele 1995
[11] Application Note AN97046, Determination of Bit Timing Parameters for the
CAN Controller SJA1000 — Philips Semiconductors, 1997
[12] Application Note AN96116, PCA82C250/251 CAN Transceiver — Philips
Semiconductors, 1996
[13] Data Sheet PESD1CAN, CAN bus ESD protection diode — Philips
Semiconductors, 2005 Oct 17
AN10211_2
Application note
© NXP B.V. 2006. All rights reserved.
Rev. 02 — 10 November 2006
27 of 29
AN10211
NXP Semiconductors
TJA1040 high speed CAN transceiver
13. Legal information
13.1 Definitions
Draft — The document is a draft version only. The content is still under
internal review and subject to formal approval, which may result in
modifications or additions. NXP Semiconductors does not give any
representations or warranties as to the accuracy or completeness of
information included herein and shall have no liability for the consequences of
use of such information.
Suitability for use — NXP Semiconductors products are not designed,
authorized or warranted to be suitable for use in medical, military, aircraft,
space or life support equipment, nor in applications where failure or
malfunction of a NXP Semiconductors product can reasonably be expected to
result in personal injury, death or severe property or environmental damage.
NXP Semiconductors accepts no liability for inclusion and/or use of NXP
Semiconductors products in such equipment or applications and therefore
such inclusion and/or use is at the customer’s own risk.
Applications — Applications that are described herein for any of these
products are for illustrative purposes only. NXP Semiconductors makes no
representation or warranty that such applications will be suitable for the
specified use without further testing or modification.
13.2 Disclaimers
General — Information in this document is believed to be accurate and
reliable. However, NXP Semiconductors does not give any representations or
warranties, expressed or implied, as to the accuracy or completeness of such
information and shall have no liability for the consequences of use of such
information.
13.3 Trademarks
Notice: All referenced brands, product names, service names and trademarks
are the property of their respective owners.
Right to make changes — NXP Semiconductors reserves the right to make
changes to information published in this document, including without
limitation specifications and product descriptions, at any time and without
notice. This document supersedes and replaces all information supplied prior
to the publication hereof.
AN10211_2
Application note
© NXP B.V. 2006. All rights reserved.
Rev. 02 — 10 November 2006
28 of 29
AN10211
NXP Semiconductors
TJA1040 high speed CAN transceiver
14. Contents
1
2
3
3.1
3.2
3.3
4
4.1
4.1.1
4.1.2
4.2
4.3
4.4
4.5
4.6
5
5.1
5.2
5.2.1
5.2.2
5.2.3
5.3
5.4
6
7
7.1
7.2
7.3
7.3.1
7.3.2
8
8.1
8.2
9
9.1
10
10.1
11
12
13
13.1
Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
General high speed CAN application. . . . . . . . 3
Application specific requirements on high speed
CAN . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
Type A applications . . . . . . . . . . . . . . . . . . . . . 7
Type B applications . . . . . . . . . . . . . . . . . . . . . 7
Type C and D applications . . . . . . . . . . . . . . . . 7
Main features of the TJA1040 . . . . . . . . . . . . . . 8
Operation modes . . . . . . . . . . . . . . . . . . . . . . . 8
Normal mode . . . . . . . . . . . . . . . . . . . . . . . . . . 8
Standby mode. . . . . . . . . . . . . . . . . . . . . . . . . . 8
Excellent EMC behavior . . . . . . . . . . . . . . . . . . 9
Passive behavior . . . . . . . . . . . . . . . . . . . . . . . 9
Common mode stabilization, SPLIT pin . . . . . . 9
Interfacing to microcontroller with non 5V
supply . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
TXD dominant time-out function . . . . . . . . . . . 10
Hardware application . . . . . . . . . . . . . . . . . . . 11
Split termination concept . . . . . . . . . . . . . . . . 11
Optional circuitry at CANH and CANL . . . . . . 12
Common mode choke . . . . . . . . . . . . . . . . . . 12
Capacitors. . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
ESD protection . . . . . . . . . . . . . . . . . . . . . . . . 13
Buffering at VCC . . . . . . . . . . . . . . . . . . . . . . . 14
Optional circuitry at TXD and RXD . . . . . . . . . 14
Pin FMEA . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15
Bus network aspects . . . . . . . . . . . . . . . . . . . . 17
Maximum number of nodes . . . . . . . . . . . . . . 17
Maximum bus line length . . . . . . . . . . . . . . . . 18
Topology aspects . . . . . . . . . . . . . . . . . . . . . . 18
Ringing due to signal reflections. . . . . . . . . . . 19
Linear topology . . . . . . . . . . . . . . . . . . . . . . . . 19
Interoperability . . . . . . . . . . . . . . . . . . . . . . . . . 20
TJA1040 mixed with TJA1041 nodes . . . . . . . 22
TJA1040 mixed with TJA1050 or C250/C251
nodes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22
Upgrading hints . . . . . . . . . . . . . . . . . . . . . . . . 23
Hardware check list C250/C251 → TJA1040 . 24
Appendix . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25
Comparison of C250/C251, TJA1040, TJA1041
and TJA1050 . . . . . . . . . . . . . . . . . . . . . . . . . 25
Abbreviations . . . . . . . . . . . . . . . . . . . . . . . . . . 26
References . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26
Legal information. . . . . . . . . . . . . . . . . . . . . . . 28
Definitions . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28
13.2
13.3
14
Disclaimers . . . . . . . . . . . . . . . . . . . . . . . . . . 28
Trademarks . . . . . . . . . . . . . . . . . . . . . . . . . . 28
Contents. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29
Please be aware that important notices concerning this document and the product(s)
described herein, have been included in section ‘Legal information’.
© NXP B.V. 2006.
All rights reserved.
For more information, please visit: http://www.nxp.com
For sales office addresses, please send an email to: [email protected]
Date of release: 10 November 2006
Document identifier: AN10211_2