Application Note TLE7250

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
About this document . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1
Table of Contents . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2
1
CAN Application . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
2
2.1
2.2
TLE7250 Description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
Features . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
Mode Description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
3
3.1
3.2
In Vehicle Network Applications . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
Clamp 30 and Clamp 15 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
Baud Rate versus Bus Length . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
4
CAN FD . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
5
5.1
5.2
5.3
5.4
5.5
5.6
Pin Description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
VCC Pin . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
NEN and NRM Pins . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
TxD Pin . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
RxD Pin . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
CANH and CANL Pins . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
GND Pin . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
6
6.1
6.2
6.3
6.3.1
6.3.2
6.4
6.5
6.6
6.7
Transceiver Supply . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
Voltage Regulator . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
External Circuitry . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
VCC (5 V) Power Supply Concept . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
Single VCC 5 V power supply . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
Dual VCC 5 V power supply . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
Current Consumption . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
Loss of Battery (Unsupplied Transceiver) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
Loss of Ground . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
Ground Shift . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14
7
7.1
7.2
Transceiver Control . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15
Mode Change by NEN, NRM . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15
Mode Change Delay . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15
8
8.1
8.2
8.3
8.4
Failure Management . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16
TxD Dominant Time-out Detection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16
Minimum Baud Rate and Maximum TxD Dominant Phase . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16
Short Circuit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17
TLE7250 Junction Temperature . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18
Terms and Abbreviations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20
9
Revision History . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21
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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 RT = 120 Ω or
a split termination (RT/2 = 60 Ω and CT = 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.
VBAT
Power
Supply
VIO/VCC
Transceiver
CANH
CANL
Mode-Pin
CANH
TxD
CANL
RxD
μC
GND
ECU
CT
Figure 1
ECU
ECU
ECU
ECU
RT/2
RT/2
RT/2
RT/2
CT
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 VCC/2 (typ. 2.5 V) and the differential output voltage VDiff is below 0.5 V.
A “low” signal applied to TxD pin generates a dominant state on CANH and CANL. The voltage on CANH
changes towards VCC and CANL goes towards GND. The differential voltage VDiff is higher than 0.9 V.
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CAN Application
CANH
CANL
5V
“recessive”
“dominant”
“recessive”
2,5V
t
VDiff
5V
“dominant”
0,9V
0,5V
“recessive”
t
-1V
Figure 2
Voltage Levels according to ISO 11898-2
Table 1
Voltage Levels according to ISO 11898-2
Parameter
Symbol
Values
Unit
Note or Test Condition
Min.
Typ.
Max.
2.0
2.5
3.0
V
No load
Differential Output Bus Voltage VDiff_R_NM
-500
–
50
mV
No load
Differential Input Bus Voltage
VDiff_R_Range
-1.0
–
0.5
V
–
VCANH
2.75
3.5
4.5
V
50 Ω < RL < 65 Ω
VCANL
0.5
1.5
2.25
V
50 Ω < RL < 65 Ω
Differential Output Bus Voltage VDiff_D_NM
1.5
2.0
3.0
V
50 Ω < RL < 65 Ω
Differential Input Voltage
0.9
–
5.0
V
–
Recessive State
Output Bus Voltage
VCANL,H
Dominant State
Output Bus Voltage
VDiff_D_Range
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
8
NEN
GND
2
7
CANH
VCC
3
6
CANL
RxD
4
5
NRM
TxD
1
8
NEN
GND
2
7
CANH
VCC
3
6
CANL
RxD
4
5
NRM
PAD
(Top-side x-ray view)
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.
Clamp 30
Clamp 15
VBAT
ECU with
TLE7251
CT
Figure 4
ECU with
ECU with
ECU with
ECU with
TLE7251
TLE7251
TLE7250/51
TLE7250/51
RT/2
RT/2
RT/2
RT/2
CT
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
VBAT
Power
Supply
VCC
Mode
μC
TLE7250
RxD
TxD
CANH
CANL
Figure 5
Example ECU with TLE7250
3.2
Baud Rate versus Bus Length
Table 2
Recommended Baud Rate versus Bus Length
Baud Rate
(kbit/s)
Bus Length (m)
Maximum Distance between two Nodes
1000
10
500
40
250
120
125
500
50
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 = tCANcontroller + tTransceiver + tCable) until the signal arrives at node B.
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:
tprop = tCANcontroller + tTransceiver + tCable + tCANcontroller + tTransceiver + tCable =
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 118982 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
Payload (Data)
CRC
ACK
EOF
1 Mbit/s
CAN FD:
8 Byte Message
CAN FD:
Increased Payload
SOF
Arbitration
CTR
1 Mbit/s
Payload (Data)
CRC
ACK
EOF
2 Mbit/s
1 Mbit/s
SOF
Arbitration
CTR
1 Mbit/s
Payload (Data)
CRC
2 Mbit/s
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
VCC Pin
The VCC pin supplies the transmitter output stage. The transmitter operates according to data sheet
specifications in the voltage range of 4.5 V < VCC < 5.5 V. Voltage VCC > 6 V can damage the device. If VCC < VCC_UV,
then the transmitter is disabled. The undervoltage threshold VCC_UV is in the range from 3.65 V to 4.3 V. If
VCC_UV < VCC < 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 VCC, then the device enters
Power-save mode, due to the internal pull-up resistor to VCC on NEN and NRM. Table 3 shows mode changes
via the NEN and NRM pins, assuming VIO > VIO_UV. Features and modes of operation are described in Chapter 2.
Table 3
Mode Selection via NEN and NRM
Mode of Operation
NEN
NRM
Comment
Power-Save mode
“high”
“X”
If NEN is set to “high”, then the device enters Power-save
mode, independent of the logical input at NRM.
“high”
Receive-Only mode
“low”
“low”
Transmitter is disabled. The receiver is enabled and
operates as specified in the data sheet.
Normal-Operating mode
“low”
“high”
If VCC > VCC_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 VCC, 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 VIO > VIO_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 VCC. 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 Chapter 8.1). 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 VCC pin. The VCC 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 VCC pin. This
chapter describes aspects of power consumption and voltage supply concepts of TLE7250.
6.1
Voltage Regulator
It is recommended to use one of the following Infineon low drop output (LDO) voltage regulators, depending
on the VIO power supply concept:
•
5 V VCC 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 VCC 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 VCC. Changes in load profile may reduce the stability of VCC. If several CAN transceivers are connected
in parallel, and if these CAN transceivers are supplied by the same VCC power supply (for example LDO), then
the impact on the stability of VCC is even stronger. It is recommended to place a 100 nF capacitor as close as
possible to VCC pin. The output of the VCC 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
VCC (5 V) Power Supply Concept
TLE7250 offers a VCC input pin that supplies the internal logic and the transmitter output stage. VCC 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 VCC 5 V power supply
VBAT
5V LDO
VCC
μC
VCC
TLE7250
Figure 7
Single VCC (5 V) Power Supply
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Transceiver Supply
6.3.2
Dual VCC 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 VCC 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.
VBAT
VCC
5V LDO
VCC
μC
VCC
5V LDO
VCC
TLE7250
Figure 8
Dual VCC (5 V) Power Supply
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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 VCC supply is specified as 60 mA in dominant state and
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:
ICC_AVG = (ICC_REC + ICC_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 IROM = 3mA.
Typically the current consumption is less than 3mA.
•
Power-save mode and Forced-power-save mode:
In Power-save mode most of the functions are turned off. VCC can be switched off. The maximum current
consumption is specified as 12 µA.
6.5
Loss of Battery (Unsupplied Transceiver)
When TLE7250 is unsupplied, CANH and CANL act as high impedance. The leakage current ICANH,lk, ICANL,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.
VBAT
VBAT
Voltage
Regulator
Voltage
Regulator
VCC
Inductive
load
VCC
CAN Transceiver
CAN Transceiver
CANH
CANL
GND
Figure 9
GND
Loss of GND with Inductive Load
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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 (Ri) to GND.
Because the transmitting node has its GND shifted to VShift, the recessive voltage level Vrec from the chassis
ground is no longer 2.5 V but Vrec + Vshift. The same ground shift voltage VShift 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 Vrec during a ground shifted node transmitting is equal to the average recessive
voltage level of all transceivers:
Vrec = [(Vrec_1 + VShift_1) + (Vrec_2 + VShift_2) + (Vrec_3 + VShift_3) + ... + (Vrec_n + VShift_n)]/n
n: number of connected CAN nodes
Vrec_1, Vrec_2, .., Vrec_n: specific recessive voltage level of the transceiver at nodes 1, 2, .. n
VShift_1, VShift_2, ..., VShift_n: specific ground shift voltage level of the transceiver at nodes 1, 2, .. n
The supply current of a ground shifted transceiver increases by ICC_Shift = VShift / (Ri_n / n), assuming all input
resistances at CANH and CANL of the transceivers are identical.
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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 VCC.
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 tMode. The
transition time period tMode 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 tMode 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 tMode, 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
Figure 10
Mode change
tMode
Normal-operating mode / Receive-only mode
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 tTXD_release = 200 ns to reset the TxD dominant timer.
TxD
t
t > tTxD_release
t > tTxD
t < tTxD_release
CANH
CANL
t
RxD
t
TxD time-out
Figure 11
TxD time–out released
Resetting TxD Dominant Time-out Detection
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 tTxD = 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.
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Failure Management
8.3
Short Circuit
Figure 12 shows short circuit types on the HS CAN bus. The CANH and CANL pins are short circuit proof to GND
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 VBAT, 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
VBAT Case 3
VCC
CANH
Case 5
Case 2
VBAT Case 4
Case 7
VCC
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 VBAT (Case 2) or VCC (Case 4)
If a short circuit occurs, then the VCC supply current for the transceiver can increase significantly. It is
recommended to dimension the voltage regulator for the worst case, especially when VCC also supplies the
microcontroller. VCC supply current only increases in dominant state. The recessive current remains almost
unchanged.
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.
The average fault current with worst case parameters and assuming a realistic duty cycle of 10% is:
ICC,Fault = ICC,rec x 0.9 + I CANH,SC x 0.1 = 13.6mA.
CANL shorted to VBAT
If CANL is shorted to VBAT, 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, VBAT 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 VBAT x 100mA = 0.1 x 18V x 100mA = 0.18W.
CANH shorted to VBAT
Short circuit of CANH to VBAT 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
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Failure Management
circuit of CANH to VBAT occurs, then the power loss in the termination resistor must be taken into account.
Figure 13 shows the current in case CANH is shorted to VBAT. 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:
PLoss_Termination = 0.1 x (RTermination x ICANL,SC)x ICANL,SC= (60Ω x 100mA) x 100mA = 0.6W
PLoss_CANL = 0.1 x (VBAT - (RTermination x ICANL,SC)) x ICANL,SC)= 0.1 x (18V-6V) x 100mA = 0.1 x 12V x 100mA = 0.12W
CANH shorted to VBAT
CANH
CANH
ICANL_SC
CAN
Transceiver
CAN
Transceiver
60Ω
CANL
CANL
Figure 13
Current Flowing in Case of a Short Circuit CANH to VBAT
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:
PNM,MAX = D × (ICC_R × VCC,max) + D × (ICC_D x VCC,max) + (IO × VIO,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 VCC and VIO have their typical values instead of maximum values.
Power dissipation is much lower for such typical conditions:
PNM,AVG = D × (ICC_R,Typ × VCC,AVG) + D × (ICC_D,Typ x VCC,AVG) + (IO,Typ × VIO,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 ∆Tj
Package
Rthja
∆Tj
Conditions
PG-DSO-8
120 K/W
22.1 K
PG-TSON-8
65 K/W
12 K
PNM,MAX = 184.25 mW;
Tamb = 150 °C;
50% duty cycle;
VCC = VCC,max; VIO = VIO,max
PG-DSO-8
120 K/W
2.8 K
PG-TSON-8
65 K/W
1.5 K
PG-DSO-8
120 K/W
6K
PG-TSON-8
65 K/W
3.25K
PG-DSO-8
120 K/W
21.62K
PG-TSON-8
65 K/W
11.72K
Application Note
18
PNM,AVG = 23.3 mW;
Tamb = 80 °C;
10% duty cycle;
VCC = VCC,typ; VIO = VIO,typ
Short Circuit CANH to GND
10% duty cycle;
Short Circuit CANL to VBAT
10% duty cycle;
Rev. 1.1
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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
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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
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Revision History
9
Revision History
Revision
Date
Changes
1.1
2016-05-03
TxD Dominant time-out detection updated Figure 11;
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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Edition 2016-05-03
Published by
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81726 Munich, Germany
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Z8F54978220
IMPORTANT NOTICE
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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
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and all information given in this application note.
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