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Z8F54978220
Application Note
TLE7250
About this document
Scope and purpose
This document provides application information for the transceiver TLE7250 from Infineon Technologies AG as Physical Medium Attachment within a Controller Area Network (CAN).
This document contains information about:
• set-ups for CAN application
• mode control
• fail safe behavior
• power supply concepts
• power consumption aspects
This document refers to the data sheet of the Infineon Technologies AG CAN Transceiver TLE7250.
Note: The following information is given as a hint for the implementation of our devices only and shall not be regarded as a description or warranty of a certain functionality, condition or quality of the device.
Intended audience
This document is intended for engineers who develop applications.
Application Note www.infineon.com
1 Rev. 1.1
2016-05-03
Application Note
Z8F54978220
Table of Contents
V
CC
Pin . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
V
CC
(5 V) Power Supply Concept . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
CC
CC
5 V power supply . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
5 V power supply . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
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CAN Application
1 CAN Application
With the growing number of electronic modules in cars the amount of communication between modules increases. In order to reduce wires between the modules CAN was developed. CAN is a Class-C, multi master serial bus system. All nodes on the bus system are connected via a two wire bus. A termination of R
T a split termination (R
T/2
= 60 Ω and C
T
= 120 Ω or
= 4.7 nF) on two nodes within the bus system is recommended.
Typically an ECU consists of:
• power supply
• microcontroller with integrated CAN protocol controller
• CAN transceiver
The CAN protocol uses a lossless bit-wise arbitration method of conflict resolution. This requires all CAN nodes to be synchronized. The complexity of the network can range from a point-to-point connection up to hundreds
of nodes. A simple network concept using CAN is shown in Figure 1
.
V
BAT
Power
Supply
CANH
CANL
V
IO
/V
CC
Transceiver
Mode-Pin
CANH
CANL
TxD
RxD
μC
GND
ECU ECU ECU ECU ECU
R
T/2
R
T/2
R
T/2
R
T/2
C
T
C
T
Figure 1 CAN Example with Typical ECU Using TLE7250
The CAN bus physical layer has two defined states: dominant and recessive. In recessive state CANH and CANL are biased to V
CC
/2 (typ. 2.5 V) and the differential output voltage V
A “low” signal applied to TxD pin generates a dominant state on CANH and CANL. The voltage on CANH changes towards V
CC
Diff
is below 0.5 V.
and CANL goes towards GND. The differential voltage V
Diff
is higher than 0.9 V.
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CAN Application
CANH
CANL
“recessive” “dominant”
V
Diff
“dominant”
“recessive”
5V
“recessive”
2,5V t
5V
0,9V
0,5V t
-1V
Table 1
Parameter
Voltage Levels according to ISO 11898-2
Symbol Values
Min.
Typ.
Max.
Recessive State
Output Bus Voltage
V
CANL,H
Differential Output Bus Voltage V
Diff_R_NM
Differential Input Bus Voltage
V
Diff_R_Range
Dominant State
Output Bus Voltage
V
CANH
V
CANL
Differential Output Bus Voltage V
Diff_D_NM
Differential Input Voltage
V
Diff_D_Range
2.0
-500
2.75
0.5
1.5
0.9
2.5
–
-1.0 –
3.5
1.5
2.0
–
3.0
50
0.5
4.5
2.25
3.0
5.0
Unit
V mV
V
V
V
V
V
Note or Test Condition
No load
No load
–
50 Ω < R
50 Ω < R
50 Ω < R
–
L
L
L
< 65 Ω
< 65 Ω
< 65 Ω
The CAN physical layer is described in ISO 11898-2. The CAN transceiver TLE7250 fulfills all parameters defined in ISO 11898-2. This document describes CAN applications with the TLE7250. It provides application hints and recommendations for the design of CAN electronic control units (ECUs) using the CAN transceiver TLE7250 from Infineon Technologies AG.
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TLE7250 Description
2 TLE7250 Description
The transceiver TLE7250 represents the physical medium attachment, interfacing the CAN protocol controller to the CAN transmission medium. The transmit data stream of the protocol controller at the TxD input is converted by the CAN transceiver into a bus signal. The receiver of the TLE7250 detects the data stream on the
CAN bus and transmits it via the RxD pin to the protocol controller.
2.1
Features
The main features of the TLE7250 are:
• Baud rate up to 2 Mbit/s
• Very low Electromagnetic Emission (EME) and high Electromagnetic Immunity (EMI)
• Excellent ESD performance according to HBM (+/-9 kV) and IEC (+/-8 kV)
• Very low current consumption in Power-save mode
• Transmit data (TxD) dominant time-out function
• Supply voltage range 4.5 V to 5.5 V
• Thermal shutdown protection
2.2
Mode Description
The TLE7250 supports three different modes of operation. The mode of operation depends on the status of the mode selection pin NEN, NRM,:
• Normal-operating mode: Used for communication on the HS CAN bus. Transmit and receive data on the bus.
• Receive-only mode: Allows diagnostics (to avoid the acknowledge bit (ACK) implemented by software), to check modules connections or to avoid communication errors on the bus due to microcontroller failure.
Blocking babbling idiots from disturbing communication. Used for Pretended Networking to set ECU and microcontroller to low-power mode, waiting for a specific message to switch to Normal-operating mode.
Pretended Networking is used to reduce current consumption of ECUs.
• Power-save mode: Reduces current consumption in afterrun when there is no communication on the HS
CAN bus with ECU still active. Emergency undervoltage state, when the microcontroller detects undervoltage and starts saving internal information. In order to reduce current consumption the transceiver is set to Power-save mode.
TxD 1
GND
2
V
CC
3
RxD 4
PAD
8
NEN
7
CANH
6
CANL
5
NRM
(Top-side x-ray view)
TxD
GND
V
CC
RxD
1
2
3
4
8
7
6
5
NEN
CANH
CANL
NRM
Figure 3 Pin Configuration of the TLE7250
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In Vehicle Network Applications
3 In Vehicle Network Applications
The TLE7250/51-Family offers a perfect match for various ECU requirements. For partially supplied ECUs
(Clamp 15) the TLE7250 is suitable. According to the requirements of automobile manufacturers, the modules can either be permanently supplied or unsupplied during the car is parked. The main reason for unsupplied modules is saving battery energy. Permanently supplied modules can wake up quickly via CAN message.
3.1
Clamp 30 and Clamp 15
Clamp 30:
Permanently supplied modules, even when the car is parked are required by body applications such as door modules, RF keyless entry receivers, etc. Modules are directly connected to the battery. This supply line is called clamp 30. As battery voltage is present permanently, the voltage regulator, transceiver and microcontroller are always supplied. Therefore voltage regulator, transceiver and microcontroller need to be set to low-power mode in order to reduce current consumption to a minimum.
Clamp 15:
Partially supplied modules are typically used in under hood applications such as ECUs. When the car is parked a main switch or ignition key switches off the battery supply. This supply line is called clamp 15. When the battery voltage is not present, the voltage regulator and transceiver are switched off.
V
BAT
Clamp 30 Clamp 15
ECU with
TLE7251
ECU with
TLE7251
ECU with
TLE7251
ECU with
TLE7250/51
ECU with
TLE7250/51
R
T/2
R
T/2
C
T
R
T/2
R
T/2 C
T
Figure 4 CAN with ECUs Using TLE7250
In Clamp 15 applications there is no need to use transceivers with bus wake-up feature. Therefore TLE7250
offers three different modes, that make applications more flexible (see Chapter 2.2
). For applications that do not use the bus wake-up feature, the TLE7250 offers the Power-save mode with very low current consumption.
There is also the possibility to reduce the current consumption of the ECU more by disconnecting the TLE7250 from the power supply. If communication is still on the HS CAN bus, then the TLE7250 has a perfect passive bus behavior in order not to affect CAN bus communication, while the TLE7250 is switched off.
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In Vehicle Network Applications
V
BAT
Power
Supply
V
CC
μC
Mode
RxD
TxD
TLE7250
CANH
CANL
Figure 5 Example ECU with TLE7250
3.2
Baud Rate versus Bus Length
500
250
125
50
Table 2
Baud Rate
(kbit/s)
1000
Recommended Baud Rate versus Bus Length
Bus Length (m)
Maximum Distance between two Nodes
10
40
120
500
1000
Baud rate is limited by:
• bus length
• ringing
• propagation delay of cables
• propagation delay of the CAN controller of the transceiver
The two most distant nodes (A and B) in a CAN network are the limiting factor in transmission speed. The propagation delays must be considered because a round trip has to be made from the two most distant CAN controllers on the bus.
Worst case scenario: When node A starts transmitting a dominant signal, it takes a certain period of time
(t = t
CANcontroller
+ t
Transceiver
+ t
Cable
) until the signal arrives at node B.
t
The propagation delay is estimated by: CAN controller delay, transceiver delay, bus length delay. Assumption:
70 ns for CAN controller, 255 ns for transceiver, 5 ns per meter of cable. Example with 50 m cable length: prop
= t
CANcontroller
+ t
Transceiver
+ t
Cable
+ t
CANcontroller
+ t
Transceiver
+ t
Cable
=
70 ns + 255 ns + 50 m × 5 ns/m + 70 ns + 255 ns + 50 m × 5 ns/m = 1150 ns
Some other factors of great influence on the maximum baud rate are cable capacitance, oscillator tolerance, ringing and reflection effects depending on the network topology. In addition to theoretical maximum propagation delay all other effects must be taken into account and an additional margin of safety must be added. Wire resistance increases with bus length and therefore the bus signal amplitude may be degraded.
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CAN FD
4 CAN FD
CAN FD (Flexible Data Rate) is the advanced version of classical CAN. Classical CAN is specified by ISO 11898-2 for data transmission rate up to 1 Mbit/s. For CAN FD with higher data transmission rate (2 Mbit/s) ISO 11898-
2 specifies additional timing parameters. CAN FD uses the same physical layer as classical CAN does, but allows higher data transmission rate and increased payload per message. During the arbitration phase and checksum the data transmission rate is the same as for classical CAN (1 Mbit/s). As soon as one node in the CAN
FD network starts transmitting the payload, the data rate increases (2 Mbit/s). The increase in baud rate is possible as only one node transmits during the data transmission phase. All other nodes listen to the data on the CAN bus. Instead of 8 bytes per message (classical CAN) payload is increased up to maximum 64 byte per message. Using CAN FD saves transmission time and allows increased data payload. In order to ensure reliable data transmission, CAN FD requires a CAN transceiver with full ISO 11898-2 specification for Flexible Data rate up to 2 Mbit/s.
The TLE7250 from Infineon Technologies AG is the perfect match for CAN FD networks. TLE7250 fulfills or exceeds all classical CAN and CAN FD parameters of ISO 11898-2 in order to enable smooth and safe usage within applications.
Classical CAN:
8 Byte Message
SOF
Arbitration
CTR
CAN FD:
8 Byte Message
SOF
Arbitration
CTR
1 Mbit/s
Payload (Data)
CRC
1 Mbit/s
Payload (Data)
CRC
2 Mbit/s
ACK
EOF
1 Mbit/s
CAN FD:
Increased Payload
SOF
Arbitration
CTR
1 Mbit/s
Payload (Data)
CRC
2 Mbit/s
ACK
EOF
ACK
EOF
1 Mbit/s
t
Figure 6 Classical CAN Data Rate and CAN FD Data Rate
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Pin Description
5 Pin Description
5.1
V
CC
Pin
The V
CC
pin supplies the transmitter output stage. The transmitter operates according to data sheet specifications in the voltage range of 4.5 V < V
CC
< 5.5 V. Voltage V then the transmitter is disabled. The undervoltage threshold V
CC
> 6 V can damage the device. If V
CC_UV
CC
< V
CC_UV
is in the range from 3.65 V to 4.3 V. If
V
CC_UV
< V
CC
< 4.5 V, then the transmitter is enabled and can then send data to the bus, but parameters may be outside the specified range.
,
5.2
NEN and NRM Pins
The NEN pin and the NRM set the mode of TLE7250 and are usually directly connected to output ports of a microcontroller. If the mode pins are unconnected and TLE7250 is supplied by V
CC
, then the device enters
Power-save mode, due to the internal pull-up resistor to V
CC via the NEN and NRM pins, assuming V
IO
> V
IO_UV
on NEN and NRM. Table 3 shows mode changes
. Features and modes of operation are described in
Table 3 Mode Selection via NEN and NRM
Mode of Operation
Power-Save mode
NEN
“high”
NRM
“high” “X”
Receive-Only mode
Normal-Operating mode
Comment
If NEN is set to “high”, then the device enters Power-save mode, independent of the logical input at NRM.
“low” “low” Transmitter is disabled. The receiver is enabled and operates as specified in the data sheet.
“low” “high” If V
CC
> V
CC_UV
, then the transmitter is enabled.
Power-save mode is the low-power mode of TLE7250. In Power-save mode both the transmitter and the receiver are disabled and current consumption is reduced to a minimum. The user can deactivate the transmitter of TLE7250 either by setting the NEN pin to “high” or setting the NRM pin to “low”. This can be used to implement two different fail safe paths.
For disconnected mode pins or microcontroller ports in “tristate” the TLE7250 has an integrated pull-up resistor to V
CC
, by default the device is in Power-save mode in order to enable low current consumption.
5.3
TxD Pin
TxD is an input pin. TxD pin is used to receive the data stream from the microcontroller. If V
IO
> V
IO_UV
, then the data stream is transmitted to the HS CAN bus. A “low” signal causes a dominant state on the bus and a “high” signal causes a recessive state on the bus. The TxD input pin has an integrated pull-up resistor to V
CC
. If TxD is permanently “low”, for example due to a short circuit to GND, then the TxD time-out feature will block the signal on the TxD input pin (see
). It is not recommended to use a series resistor within the TxD line between transceiver and microcontroller. A series resistor may add delay, which degrades the performance of the transceiver, especially in high data rate applications. The data stream sent from the microcontroller to the
TxD pin of the transceiver is only transmitted to the HS CAN bus in Normal-operating mode. In all other modes the TxD input pin is blocked.
5.4
RxD Pin
RxD is an output pin. The data stream received from the HS CAN bus is displayed on the RxD output pin in
Normal-operating mode, Receive-only mode. It is not recommended to use a series resistor within the RxD
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Pin Description line between transceiver and microcontroller. A series resistor may add delay, which degrades the performance of the transceiver, especially in high data rate applications.
5.5
CANH and CANL Pins
CANH and CANL are the CAN bus input and output pins. The TLE7250 is connected to the bus via pin CANH and
CANL. Transmitter output stage and receiver are connected to CANH and CANL. Data on the TxD pin is transmitted to CANH and CANL and is simultaneously received by the receiver input and signalled on the RxD output pin. For achieving optimum EME (Electromagnetic Emission) performance, transitions from dominant to recessive and from recessive to dominant are done as smooth as possible also at high data rate. Output
levels of CANH and CANL in recessive and dominant state are described in Table 1
. Due to the excellent ESD performance on CANH and CANL no external ESD components are necessary to fulfill OEM requirements.
5.6
GND Pin
The GND pin must be connected as close as possible to module ground in order to reduce ground shift. It is not recommended to place filter elements or an additional resistor between GND pin and module ground. GND must be the same for transceiver, microcontroller and HS CAN bus system.
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Transceiver Supply
6 Transceiver Supply
The internal logic of TLE7250 is supplied by the V
CC
pin. The V
CC
pin 5 V supply is used to create the CANH and
CANL signal. The transmitter output stage as well as the main CAN bus receiver are supplied by the V chapter describes aspects of power consumption and voltage supply concepts of TLE7250.
CC
pin. This
6.1
Voltage Regulator
It is recommended to use one of the following Infineon low drop output (LDO) voltage regulators, depending on the V
IO
power supply concept:
• 5 V V
CC
power supply: TLS850D0TAV50 (500mA), TLS850F0TA V50 (500mA), TLS810D1EJV50 (100mA),
TLS810B1LDV50 (100mA), TLE4266-2 (150mA)
• Dual 5V voltage power supply: TLE4473GV55
Please refer to Infineon Linear Voltage Regulators for the Infineon voltage regulator portfolio, data sheets and application notes.
6.2
External Circuitry
In order to reduce EME and to improve the stability of input voltage level on V
CC
of the transceiver, it is recommended to place capacitors on the PCB. During sending a dominant bit to the HS CAN bus, current consumption of TLE7250 is higher than during sending a recessive bit. Data transmission can change the load profile on V
CC
. Changes in load profile may reduce the stability of V the impact on the stability of V
CC possible to V
CC
pin. The output of the V
CC
CC
. If several CAN transceivers are connected in parallel, and if these CAN transceivers are supplied by the same V
CC
power supply (for example LDO), then
is even stronger. It is recommended to place a 100 nF capacitor as close as
power supply (for example LDO) must be stabilized by a capacitor in the range of 1 to 50 µF, depending on the load profile. Ceramic capacitors are recommended for low ESR.
6.3
V
CC
(5 V) Power Supply Concept
TLE7250 offers a V
CC
input pin that supplies the internal logic and the transmitter output stage. V
CC
must be connected to a 5 V voltage regulator. Also the microcontroller must be supplied with 5 V in order to adapt the digital and output levels of the microcontroller to the transceiver. A single voltage regulator can supply both the transceiver and the microcontroller.
6.3.1
Single V
CC
5 V power supply
V
BAT
5V LDO
V
CC
μC
V
CC
TLE7250
Figure 7 Single (5 V) Power Supply
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Transceiver Supply
6.3.2
Dual V
CC
5 V power supply
It is possible to use two separate 5 V voltage regulators. If other components are connected to the 5 V voltage regulator that cause noise and transients on the V
CC
voltage output of the voltage regulator, then two separate
5 V voltage regulators are useful. Transients disturb the HS CAN Signal and may also increase EME. In order to avoid this coupling the user can separate the power supplies of microcontroller and transceiver by placing two
5 V voltage regulators like TLS810D1EJV50 or a dual 5 V voltage regulator like TLE4473GV55 .
V
BAT
5V LDO
V
CC
V
CC
μC
Figure 8 Dual (5 V) Power Supply
5V LDO
V
CC
V
CC
TLE7250
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Transceiver Supply
6.4
Current Consumption
Current consumption depends on the mode of operation:
• Normal-operating mode:
Maximum current consumption of TLE7250 on the V
CC
supply is specified as 60 mA in dominant state and
I
5 mA in recessive state. To estimate theoretical current consumption in Normal-operating mode, a duty cycle of 50% can be assumed, with fully loaded bus communication of 50% dominant and 50% recessive.
In Normal-operating mode the TLE7250 consumes in worst case maximum:
CC_AVG
= (I
CC_REC
+ I
CC_DOM
) / 2 = 32.5 mA
Typically the current consumption is less than 15 mA.
• Receive-only mode :
In Receive-only mode the TLE7250 has a worst case maximum current consumption of I
Typically the current consumption is less than 3mA.
ROM
= 3mA.
• Power-save mode and Forced-power-save mode:
In Power-save mode most of the functions are turned off. V consumption is specified as 12 µA.
CC
can be switched off. The maximum current
6.5
Loss of Battery (Unsupplied Transceiver)
When TLE7250 is unsupplied, CANH and CANL act as high impedance. The leakage current I
CANH,lk
, I
CANL,lk
at
CANH pin or CANL pin is limited to +/- 5 µA in worst case. When unsupplied, TLE7250 behaves like a 1 MΩ resistor towards the bus. Therefore the device perfectly fits applications that use both Clamp 15 and Clamp 30.
6.6
Loss of Ground
If loss of ground occurs, then the transceiver is unsupplied and behaves like in unpowered state.
In applications with inductive load connected to the same GND, for example a motor, the transceiver can be damaged due to loss of ground. Excessive current can flow through the CAN transceiver when the inductor demagnetizes after loss of ground. The ESD structure of the transceiver cannot withstand that kind of
Electrical Overstress (EOS). In order to protect the transceiver and other components of the module, an inductive load must be equipped with a free wheeling diode.
V
BAT
Voltage
Regulator
V
CC
CAN Transceiver
V
BAT
Voltage
Regulator
V
CC
CAN Transceiver
Inductive load
CANH
CANL
GND
Figure 9 Loss of GND with Inductive Load
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GND
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Transceiver Supply
6.7
Ground Shift
Due to ground shift the GND levels of CAN transceivers within a network may vary. Ground shift occurs in high current applications or in modules with long GND wires. The receiver input stage acts like a resistor (R i
) to GND.
Because the transmitting node has its GND shifted to V ground is no longer 2.5 V but V rec
+ V shift
Shift
, the recessive voltage level V
. The same ground shift voltage V
Shift rec
from the chassis
must be taken into account for the dominant signal. Because CAN uses a differential signal and because of the wide common mode range of +/-
12 V for Infineon transceivers, any CANH and CANL DC value within absolute maximum ratings works.
The recessive CAN bus level V rec voltage level of all transceivers:
during a ground shifted node transmitting is equal to the average recessive
V
rec
= [(V rec_1
+ V
Shift_1
) + (V rec_2
+ V
Shift_2 n: number of connected CAN nodes
) + (V rec_3
+ V
Shift_3
) + ... + (V rec_n
+ V
Shift_n
)]/n
V
rec_1
, V rec_2
, .., V rec_n
: specific recessive voltage level of the transceiver at nodes 1, 2, .. n
V
Shift_1
, V
Shift_2
, ..., V
Shift_n
: specific ground shift voltage level of the transceiver at nodes 1, 2, .. n
The supply current of a ground shifted transceiver increases by I
CC_Shift resistances at CANH and CANL of the transceivers are identical.
= V
Shift
/ (R i_n
/ n), assuming all input
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Transceiver Control
7 Transceiver Control
The modes of the TLE7250 are controlled by the pins NEN, NRM.
7.1
Mode Change by NEN, NRM
The mode of operation is set by the mode selection pins NEN, NRM. By default the NRM input pin and the NEN input pin are “high” due to the internal pull-up resistor to V
CC
.
The TLE7250 is in Power-save mode independent of the status of NRM. In order to change the mode to Receiveonly mode, NEN and NRM must be switched to “low”. In order to change the mode to Normal-operating mode,
NEN must be switched to “low” and NRM must be “high”.
7.2
Mode Change Delay
The HS CAN transceiver TLE7250 changes the mode of operation within the transition time period t transition time period t
Mode
Mode
the RxD output pin is permanently set to “high” and does not reflect the status on the CANH and CANL input pins. In addition, during t
Mode
Mode
. The
must be considered in developing software for the application. During the mode change from Power-save mode to a non-low power mode the receiver and/or transmitter is enabled. During the period t
, the TxD path is blocked as well. When the mode change is
completed, the TLE7250 releases the RxD output pin. Figure 10
shows this scenario.
CANH
CANL t
RxD blocked RxD released
RxD t
NEN t
Power-save mode
Mode change t
Mode
Normal-operating mode / Receive-only mode
Figure 10 RxD Behavior during Mode Change
The RxD output pin is not blocked nor be set to “high” during the following mode changes:
• Normal-operating mode → Receive-only mode
• Receive-only mode → Normal-operating mode
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Failure Management
8 Failure Management
This chapter describes typical bus communication failures.
8.1
TxD Dominant Time-out Detection
The TxD dominant time-out detection of TLE7250 protects the CAN bus from being permanently driven to dominant level. When detecting a TxD dominant time-out, the TLE7250 disables the transmitter in order to release the CAN bus. Without the TxD dominant time-out detection, a CAN bus would be clamped to the dominant level and therefore would block any data transmission on the CAN bus. This failure may occur for example due to TxD pin shorted to ground.
The TxD dominant time-out detection can be reset after a dominant to recessive transition at the TxD pin. A
“high” signal must be applied to the TxD input for at least t
TXD_release
= 200 ns to reset the TxD dominant timer.
TxD t t > t
TxD_release t > t
TxD
CANH
CANL t < t
TxD_release t
RxD t
TxD time-out
Figure 11 Resetting TxD Dominant Time-out Detection
TxD time–out released
If a TxD Dominant Time-out is present, then a mode change to Power-save mode clears the TxD dominant timer state.
8.2
Minimum Baud Rate and Maximum TxD Dominant Phase
Due to the TxD dominant time-out detection of the TLE7250 the maximum TxD dominant phase is limited by the minimum TxD dominant time-out time t
TxD
= 4.5ms. The CAN protocol allows a maximum of 11 subsequent dominant bits at TxD pin (worst case dominant bits followed immediately by an error frame). With a minimum value of 4.5 ms given in the datasheet and maximum possible 11 dominant bits, the minimum baud rate of the application must be higher than 2.44 kbit/s.
Application Note 16 Rev. 1.1
2016-05-03
Application Note
Z8F54978220
Failure Management
8.3
Short Circuit
and to supply voltage. A current limiting circuit protects the transceiver from damage. If the device heats up due to a permanent short at CANH or CANL, then the overtemperature protection switches off the transmitter.
Depending on the type of short circuit on CANH and CANL, communication might be still possible. If only CANL is shorted to GND or only CANH is shorted to V
BAT
, then dominant and recessive states may be recognized by the receiver. Timings and/or differential output voltages might be not valid according to ISO11898 but still in the range for the receiver working properly.
Case 1
V
BAT Case 3
V
CC
CANH
Case 5
V
BAT
Case 4
V
CC
Case 7
Case 2
CANL
Case 6
Figure 12 HS CAN Bus Short Circuit Types
Communication on the HS CAN bus is blocked in the following cases:
• CANH and CANL shorted (Case7)
• CANH shorted to GND (Case 5)
• CANL shorted to V
BAT
(Case 2) or V
CC
(Case 4)
If a short circuit occurs, then the V microcontroller. V unchanged.
CC
CC
supply current for the transceiver can increase significantly. It is recommended to dimension the voltage regulator for the worst case, especially when V
CC
also supplies the
supply current only increases in dominant state. The recessive current remains almost
CANH shorted to GND
The datasheet specifies a maximum short circuit current of 100mA. When transmitting a dominant state to the bus, 5V is shorted to GND through the transmitter output stage. Power dissipation with 10% duty cycle (DCD) is:
P = DCD x U x I = 0.1 x 5V x 100mA = 0.05W.
I
The average fault current with worst case parameters and assuming a realistic duty cycle of 10% is:
CC,Fault
= I
CC,rec x 0.9 + I
CANH,SC x 0.1 = 13.6mA.
CANL shorted to V
BAT
If CANL is shorted to V
BAT
, then the current through the CANL output stage is even higher and the device heats up faster. The datasheet specifies a maximum short circuit current of 100mA. When transmitting a dominant state to the bus, V
BAT
is shorted to GND through the transmitter output stage. Assuming a realistic duty cycle of 10% for this case and the power dissipation is:
P = DCD x U x I = 0.1 x V
BAT x 100mA = 0.1 x 18V x 100mA = 0.18W.
CANH shorted to V
BAT
Short circuit of CANH to V
BAT
can result in a permanent dominant state on the HS CAN bus, due to the voltage drop at the termination resistor. Therefore the termination resistor has to be chosen accordingly. If a short
Application Note 17 Rev. 1.1
2016-05-03
Application Note
Z8F54978220
Failure Management circuit of CANH to V
Loss_Termination
BAT
= 0.1 x (R
occurs, then the power loss in the termination resistor must be taken into account.
shows the current in case CANH is shorted to V
Termination x I
CANL,SC
)x I
CANL,SC
BAT
. When transmitting a dominant state to the bus, the current flows through the termination resistor an CANL to GND. Power loss in the termination resistor and
CANL assuming a battery voltage of 18 V and a duty cycle of 10% is:
P = (60Ω x 100mA) x 100mA = 0.6W
P
Loss_CANL
= 0.1 x (V
BAT
- (R
Termination x I
CANL,SC
)) x I
CANL,SC
)= 0.1 x (18V-6V) x 100mA = 0.1 x 12V x 100mA = 0.12W
CANH
CANH shorted to V
BAT
CANH
I
CANL_SC
CAN
Transceiver
60Ω
CAN
Transceiver
CANL
CANL
Figure 13 Current Flowing in Case of a Short Circuit CANH to V
BAT
8.4
TLE7250 Junction Temperature
In Normal-operating mode highest power dissipation occurs with 50% duty cycle (D) at an ambient temperature of 150 °C:
P
NM,MAX
= D × (I
CC_R
× V
CC,max
) + D × (I
CC_D
x V
CC,max
) + (I
O
× V
IO,max
) =
= 0.5 × (4 mA × 5.5 V) + 0.5 x (60 mA × 5.5 V) + (1.5 mA × 5.5 V) = 184.25 mW.
Junction temperature increases due to power dissipation and depending on the package.
However, typical conditions are more like this: ambient temperature is below 150 °C, overall duty cycle is less than 50%, and supply voltages V
CC
and V
IO
have their typical values instead of maximum values.
Power dissipation is much lower for such typical conditions:
P
NM,AVG
= D × (I
CC_R,Typ
× V
CC,AVG
) + D × (I
CC_D,Typ
x V
CC,AVG
) + (I
O,Typ
× V
IO,AVG
= 0.9 × (2 mA × 5 V) + 0.1 x (38 mA × 5 V) + (1 mA × 3.3 V) = 23.3 mW.
) =
Table 4 Increase of Junction Temperature ∆T j
Package
PG-DSO-8
R
thja
120 K/W
∆T
j
22.1 K
PG-TSON-8
PG-DSO-8
PG-TSON-8
PG-DSO-8
PG-TSON-8
PG-DSO-8
PG-TSON-8
65 K/W
120 K/W
65 K/W
120 K/W
65 K/W
120 K/W
65 K/W
12 K
2.8 K
1.5 K
6K
3.25K
21.62K
11.72K
Conditions
P
NM,MAX
T
amb
= 184.25 mW;
= 150 °C;
50% duty cycle;
V
CC
= V
CC,max
; V
IO
= V
IO,max
P
NM,AVG
T
amb
= 23.3 mW;
= 80 °C;
10% duty cycle;
V
CC
= V
CC,typ
; V
IO
= V
IO,typ
Short Circuit CANH to GND
10% duty cycle;
Short Circuit CANL to V
BAT
10% duty cycle;
Application Note 18 Rev. 1.1
2016-05-03
Application Note
Z8F54978220
Failure Management
If a short circuit occurs, then the TLE7250 heats up. The higher the duty cycle, the higher the power dissipation and thermal shutdown can occur due to high temperature. The receiver is still enabled with only the transmitter disabled. The behavior is identical to Receive-only mode.
Application Note 19 Rev. 1.1
2016-05-03
Application Note
Z8F54978220
Terms and Abbreviations
Table 5 Terms and Abbreviations
CMC Common mode choke
EMC Electromagnetic compatibility
EME Electromagnetic emission
EMI Electromagnetic interference
EOS Electrical overstress
ESD Electrostatic discharge
ESR Equivalent Series Resistance
“high” logical high
“low” logical low
Application Note 20 Rev. 1.1
2016-05-03
Application Note
Z8F54978220
Revision History
9 Revision History
Revision Date
1.1
2016-05-03
Changes
TxD Dominant time-out detection updated
1.0
2016-01-25 Application Note created
Application Note 21 Rev. 1.1
2016-05-03
Please read the Important Notice and Warnings at the end of this document
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Trademarks updated November 2015
Other Trademarks
All referenced product or service names and trademarks are the property of their respective owners.
Edition 2016-05-03
Published by
Infineon Technologies AG
81726 Munich, Germany
© 2006 Infineon Technologies AG.
All Rights Reserved.
Do you have a question about any aspect of this document?
Email: [email protected]
Document reference
Z8F54978220
IMPORTANT NOTICE
The information contained in this application note is given as a hint for the implementation of the product only and shall in no event be regarded as a description or warranty of a certain functionality, condition or quality of the product. Before implementation of the product, the recipient of this application note must verify any function and other technical information given herein in the real application. Infineon
Technologies hereby disclaims any and all warranties and liabilities of any kind (including without limitation warranties of non-infringement of intellectual property rights of any third party) with respect to any and all information given in this application note.
The data contained in this document is exclusively intended for technically trained staff. It is the responsibility of customer’s technical departments to evaluate the suitability of the product for the intended application and the completeness of the product information given in this document with respect to such application.
For further information on technology, delivery terms and conditions and prices, please contact the nearest
Infineon Technologies Office ( www.infineon.com
).
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Technologies office.
Except as otherwise explicitly approved by Infineon
Technologies in a written document signed by authorized representatives of Infineon Technologies,
Infineon Technologies’ products may not be used in any applications where a failure of the product or any consequences of the use thereof can reasonably be expected to result in personal injury.
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