JAJSV18 July 2024 TCAN1473A-Q1
ADVANCE INFORMATION
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A typical CAN application may have a maximum bus length of 40 meters and maximum stub length of 0.3m. 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 TCAN1473A-Q1.
Many CAN organizations and standards have scaled the use of CAN for applications outside the original ISO11898-2:2016 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 ARINC825, CANopen, DeviceNet, SAEJ2284, SAEJ1939, and NMEA200.
A CAN network system design is a series of tradeoffs. In the ISO 11898-2:2016 specification the differential output driver is specified with a bus load that can range from 50Ω to 65Ω where the differential output must be greater than 1.5V. The TCAN1473A-Q1 is specified to meet the 1.5V requirement down to 50 Ω and is specified to meet 1.4V differential output at 45Ω bus load. The differential input resistance, RID, of the TCAN1473A-Q1 is a minimum of 50kΩ. If 100 TCAN1473A-Q1 transceivers are in parallel on a bus, this is equivalent to a 500Ω differential load in parallel with the nominal 60Ω bus termination which gives a total bus load of approximately 54Ω. Therefore, the TCAN1473A-Q1 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 1km 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 allowing for these system level network extensions and additional standards to build on the original ISO11898-2 CAN standard. However, when using this flexibility, the CAN network system designer must take the responsibility of good network design for a robust network operation.