Standard Termination

Split Termination

CAN

Transceiver

CAN

Transceiver

CANL

CANH

CANL

CANH

24

TCAN1044-Q1, TCAN1044V-Q1

SLLSF17A – AUGUST 2019 – REVISED DECEMBER 2019

www.ti.com

Product Folder Links: TCAN1044-Q1 TCAN1044V-Q1

Submit Documentation Feedback

Copyright © 2019, Texas Instruments Incorporated

Typical Application (continued)

Figure 18. CAN Bus Termination Concepts

9.2.2 Detailed Design Procedures

9.2.2.1 Bus Loading, Length and Number of Nodes

A typical CAN application may have a maximum bus length of 40 meters and maximum stub length of 0.3 m.

However, with careful design, users can have longer cables, longer stub lengths, and many more nodes to a bus.

A high number of nodes requires a transceiver with high input impedance such as the TCAN1044-Q1.

Many CAN organizations and standards have scaled the use of CAN for applications outside the original ISO

11898-2 standard. They made system level trade off decisions for data rate, cable length, and parasitic loading of

the bus. Examples of these CAN systems level specifications are ARINC 825, CANopen, DeviceNet, SAE J2284,

SAE J1939, and NMEA 2000.

A CAN network system design is a series of tradeoffs. In the ISO 11898-2:2016 specification the driver

differential output is specified with a bus load that can range from 50 Ω to 65 Ω where the differential output must

be greater than 1.5 V. The TCAN1044-Q1 family is specified to meet the 1.5-V requirement down to 50 Ω and is

specified to meet 1.4-V differential output at 45Ω bus load. The differential input resistance of the TCAN1044-Q1

is a minimum of 40 kΩ. If 100 TCAN1044-Q1 transceivers are in parallel on a bus, this is equivalent to a 400-Ω

differential load in parallel with the nominal 60 Ω bus termination which gives a total bus load of approximately 52

Ω. Therefore, the TCAN1044-Q1 family theoretically supports over 100 transceivers on a single bus segment.

However, for CAN network design margin must be given for signal loss across the system and cabling, parasitic

loadings, timing, network imbalances, ground offsets and signal integrity thus a practical maximum number of

nodes is often lower. Bus length may also be extended beyond 40 meters by careful system design and data rate

tradeoffs. For example, CANopen network design guidelines allow the network to be up to 1 km with changes in

the termination resistance, cabling, less than 64 nodes and significantly lowered data rate.

This flexibility in CAN network design is one of the key strengths of the various extensions and additional

standards that have been built on the original ISO 11898-2 CAN standard. However, when using this flexibility

the CAN network system designer must take the responsibility of good network design to ensure robust network

operation.