TCAN4550-Q1: How many nodes can be supported?

Praveen,

There are two parts to this question: the amount of nodes allowed and the allowable physical length of the bus.

You are correct, because the TCAN4550 adheres to the ISO11898 spec for the physical layer, it is capable of handling 30 nodes up on the bus. That's the bare minimum requirement, and it is based on the amount of input impedance that each transceiver introduces to the bus. Each CAN transceiver will have some leakage current from the bus associated with it because of this introduction of impedance, and the drivers for the CAN bus must be able to drive the correct voltage levels so that the data can be interpreted correctly by each transceiver.

Another limitation is the amount of capacitance that each CAN transceiver will introduce to the bu If there is too much capacitance, the CAN signals will get distorted by the edges "slowing down". This also plays into the limitation of bus length. The main factor limiting the bus length is the propagation delay from a CAN bit propagating down to the end of the bus and back to the originating transceiver. This needs to happen within 75% of the bit width time so that the bit can be properly sampled real-time for arbitration and determine priority

All of that being said, TI CAN transceivers are designed to allow for more than the bare minimum of 30 transceivers on the bus, and the propagation delay values are listed in the datasheet so the customer can calculate the amount of delay that the transceiver will add for the bit to get down and back the full bus length. There is a very good application note located here: www.ti.com/.../slla270.pdf. This explains what I just said but with more detail.

The input impedance of the TCAN4550 is at a minimum 30kΩ, which means theoretically 100 TCAN4550 CAN devices can be supported on one bus.

Please let me know if you have any other questions or concerns.

Regards,