SN6501-Q1
TPS76350-Q 1
Digital
Isolator
Termination
and Protection
CANH
CANL
GND
GNDi
CAN Tx
CAN Rx
GND
GNDi
GND i
Isolated Power
Isolated CAN Interface
TIDA-01255
3.3 V
3.3 V
3.3 V
5 V
5 V
T
T
T
T
Copyright © 2017, Texas Instruments Incorporated
TCAN1042-Q1
1
ZHCU217–May 2017
TIDUCN0 — http://www-s.ti.com/sc/techlit/TIDUCN0
版权 © 2017, Texas Instruments Incorporated
车用增强型隔离
CAN
参考设计
TI
参参考考设设计计：：
TIDA-01255
车车用用增增强强型型隔隔离离
CAN
参参考考设设计计
说说明明
TIDA-01255 设计专为汽车环境中广泛使用的隔离式
CAN 通信而打造。在混合动力车辆和电动车辆
(HEV/EV) 中，完整的高电压网络会相对于机箱接地浮
动。对于连接在高电压到低电压浮动系统之间的电源和
通信通道，则需要使用隔离。TIDA-01255 设计支持 通
过 简单隔离式变压器驱动器来传输功率的应用。该 TI
参考设计具有低传输延迟，可降低环路延迟并支持较高
的 CAN 波特率。
资资源源
TIDA-01255 设计文件夹
TCAN1042-Q1 产品文件夹
SN6501-Q1 产品文件夹
ISO7731-Q1 产品文件夹
TPS76350-Q1 产品文件夹
TMS570 产品文件夹
特特性性
• 灵活的高速 CAN 通信
• 低环路延迟（通常为 136ns），支持高仲裁速率
• 750mW 功率传输，具有 3kV 隔离功能
• 增强型数字隔离
• ±70V 总线故障保护
• 成本敏感型终端，具有内部 ESD 保护功能
• 符合 ISO 11898-2 CAN 标准
应应用用
• 电池监控系统
• 电池控制单元
• 混合动力电动车辆 (HEV/EV)
咨询我们的 E2E 专家
System Description
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版权 © 2017, Texas Instruments Incorporated
车用增强型隔离
CAN
参考设计
该 TI 参考设计末尾的重要声明表述了授权使用、知识产权问题和其他重要的免责声明和信息。
1 System Description
A Controller Area Network (CAN) is widely used in automotive industry to replace the complex wiring
harness with a two-wire bus. It is highly immune to electrical interference and it has ability to self-diagnose
and repair data errors. These features have led to CAN’s popularity and extended its application in
building automation, medical, and manufacturing. The TIDA-01255 design is targeted to improve the
system and CAN performance for automotive isolated ground applications such as cell supervision units,
battery control units, inverters, chargers, and so on.
CAN manages message collision and provides a unique proving ground for protocol compliance in any
application. Any CAN node may begin to transmit when the bus is free, and two or more nodes may begin
to transmit simultaneously. Arbitration is the process by which these nodes battle for control of the bus.
Proper arbitration is critical to CAN performance because this is the mechanism that guarantees that
message collisions do not reduce bandwidth or cause messages to be lost. Each data or remote frame
begins with an identifier, which assigns the priority and content of the message. As the identifier is
broadcast, each transmitting node compares the value received on the bus to the value being broadcast.
The higher priority message during a collision has a dominant bit earlier in the identifier. Therefore, if a
transmitting node senses a dominant bit on the bus in place of the recessive bit it transmitted, it interprets
this as another message with higher priority transmitting simultaneously. This node suspends transmission
before the next bit and automatically retransmits when the bus is idle.
The evolution of automotive architectures and need for efficient power train and vehicle control
mechanisms increased the demand for the number of nodes in vehicles (both passenger and commercial).
Improvement in safety architectures increases demand for internal diagnosis and data sharing between
multiple nodes with faster response times. The number of nodes to transmit and data loads push the limits
of the CAN baud rates while staying within its advantages of reliable robust communication. CAN FD
(flexible data rate) is one such flavor of CAN communications, which gained popularity for its flexibility of
retaining the features of basic CAN (no change to physical layer) and supports high data rates with little
rise in system cost.
Loop delays and round-trip delays are limiting factors in determining arbitration and data speeds (b/s) in
classical CAN. In CAN FD, loop delay and network propagation delay are the major limiting factors during
the arbitration phase. During the data phase, a secondary sampling point plays an important role for
synchronizing data in transmitters. Transceiver delay compensation, which is nothing but a loop delay and
offset, is used to check the previously transmitted data with secondary sample registers and check for bit
errors.
120 Ÿ 120 Ÿ
Loop Delay
MCU
Isolator
CAN
Transceiver
MCU
Isolator
CAN
Transceiver
MCU
CAN
Transceiver
MCU
CAN
Transceiver
MCU
CAN
Transceiver
Isolator
System Description
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4
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TIDUCN0 — http://www-s.ti.com/sc/techlit/TIDUCN0
版权 © 2017, Texas Instruments Incorporated
车用增强型隔离
CAN
参考设计
In typical ICE vehicles, loop delay and round-trip delay are straight forward to configure the transceiver
delay compensation.
• Transceiver delay compensation = Loop delay + Offset
Factors to influence loop delay in a typical CAN (non-isolated):
• Impedance of controller to transceiver interface
• Transceiver Tx-Rx delay time (dominant or recessive)
• CAN bus impedance
HEV/EV or 48-V systems are isolated from chassis ground based on system architecture. Power and
communication interfaces are isolated in high-voltage systems; ground loops are just insulated for 48-V
applications. Based on the design of control units, CAN transceivers are isolated from micro controllers as
shown in 图 2. In this case, transceiver delay compensation is increased based on the delay in the digital
isolator.
图图 2. Isolated HEV/EV or 48-V Systems
Factors to influence loop delay in an isolated CAN:
• Impedance of controller to digital isolator
• Propagation delay of digital isolator
• Impedance of digital isolator to CAN interface
• Transceiver Tx-Rx delay time (dominant or recessive)
• CAN bus impedance
Digital isolators play an important role in calculating loop delay. The propagation delay of digital isolators
has to account twice for the loop delay calculations in isolated CAN communication bus. Neglecting the
bus and controller impedance loop delay of isolated CAN is shown in 图 3.
Transceiver loop delay compensation = 2 × Propagation delay of isolator + Loop delay of Tx to Rx of CAN
transceiver
MCU
Isolator
CAN
Transceiver
Isolator
CAN
Transceiver
MCU
MCU
Isolator
CAN
Transceiver
Isolator
CAN
Transceiver
MCU
Length of the wire
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System Description
5
ZHCU217–May 2017
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版权 © 2017, Texas Instruments Incorporated
车用增强型隔离
CAN
参考设计
In a multi-master system such as CAN, it is also important to consider the round-trip delay, which supports
in gaining the arbitration of communication bus when two nodes starts transmission at the same time. The
maximum round-trip delay or propagation delay in HEV/EV depends on the topology or mounting location
of various electronic control units in the vehicle.
图图 3. Round-Trip Delay in HEV/EV
Factors to influence round-trip or propagation delay in isolated CAN:
• Impedance of controller to digital isolator
• Propagation delay of digital isolator
• Impedance of digital isolator to CAN interface
• Transceiver Tx-Rx delay time (dominant or recessive)
• CAN bus impedance
• Length of the wire
Based on the CAN physical layer, round-trip delay can be less significant. Neglecting the impedance
delays and internal software delays, the approximate round-trip delay of two isolated CAN ECUs can be
calculated as per the following equation:
Round-trip delay = 2 × (Propagation delay of digital isolator 1 + Propagation of CAN1 Tx to bus +
Propagation delay of wire + Propagation delay of CAN2 bus to Rx + Propagation delay of digital isolator 2)
1.1 Key System Specifications
表表 1. Key System Specifications
PARAMETER CONDITIONS MIN TYP MAX
TIDA-01255 loop delay CAN1 Tx to CAN1 Rx — 136 ns —
Dominant Tx to CAN bus R
L
= 60 Ω, C
L
= 4.7 ηF — 67 ns —
Recessive Tx to CAN bus 1-m wire with R
L
= 60 Ω, C
L
= 4.7 ηF — 69 ns —
Dominant CAN1 Tx to CAN2 Rx R
L
= 60 Ω, C
L
= 4.7 ηF — 115 ns —
Recessive CAN1 Tx to CAN2 Rx R
L
= 60 Ω, C
L
= 4.7ηF — 151 ns —
Rise time of CANH 1-m wire with R
L
= 60 Ω, C
L
= 4.7 ηF 30 ns 33 ns 34.31 ns
Fall time of CANH 1-m wire with R
L
= 60 Ω, C
L
= 4.7 ηF 60.4 ns 64 ns 66 ns
Operating current of TIDA-01255
CAN baud rate: 500 kbps
Isolated supply: 3.3 V
— 12 mA —
Current flowing while SCB at CAN lines
Battery voltage = 14 V
Tx = Low, CAN dominant state
— 0.862 mA —
Current flowing while SCG at CAN lines Tx = Low, CAN dominant state — 0.189 mA —
Current flowing while SCG at CAN lines
during communication at 2 Mbps
Communication is working fine — 1.29 mA —
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