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TCAN3403-Q1: Achievable Data Rate and Ringing Assessment for a 3.3V CAN-FD Transceiver

Seung Hyun Oh
Prodigy 70 points

Part Number: TCAN3403-Q1
Other Parts Discussed in Thread: TCAN3404-Q1, ESD2CANXL24-Q1, ESD2CAN24-Q1

Dear TI Team,

We are reviewing a CAN-FD interface design at Sehwa using 3.3V-powered transceivers and would appreciate your guidance on the achievable data rate and potential ringing issues.

Our planned configuration is as follows:

  • Number of nodes: 14
  • CAN bus trace length on the backplane: approximately 50 cm
  • Maximum stub length per node: approximately 4 cm
  • Termination at both ends of the bus
  • Arbitration and data-phase bit rates configured separately

Here, 3.3V refers to the transceiver supply voltage (VCC), rather than the logic interface supply voltage (VIO).

Could you please advise on the following?

  1. What data-phase bit-rate range and practical upper limit would you recommend for this configuration using 3.3V-powered transceivers, assuming bus ringing is negligible?
  2. How would the loading of 14 nodes and reflections from the stubs affect ringing and the achievable data rate, particularly the signal settling time relative to the sampling point?
  3. Could you recommend suitable TI 3.3V-powered transceivers and provide guidance on termination, protection components, PCB routing, and bit timing?

Please let us know if additional schematic or PCB information is needed for your assessment.

Best regards,
[Oh seung hyun]
Sehwa

  • 0
    TI__Guru* 81612 points

    Hi Sehwa, 

    In short: This is well within the data sheet's design considerations (9.2.2) per the CAN's standard (should be applicable to all devices) and should not be a concern for up to the data rates mentioned in the data sheet. For additional guidance, see 9.5.1 / figure 9-8 of the data sheet. Please see this app note to help clarify your specific use-case. Hence:

    1. Recommendation: target 1–5 Mbps for the data phase, with 5 Mbps as the design upper limit. Treat 8 Mbps as validation-dependent on the overall system environment. Arbitration phase at 500 kbps–1 Mbps as usual.

    2. DC loading is not your constraint. The TCAN340x-Q1 family has ≥22 kΩ differential input resistance, and the data sheet states that > 50 transceivers theoretically fit on one bus segment — though practical node count is lower due to signal loss, parasitics, timing, imbalance, and ground offsets 3. Your 4 cm stubs are well below the 0.3 m typical maximum stub length mentioned by the data sheet 3, and a cited CAN-FD network specification permits up to 30 nodes and 0.5 m branches 4.

    Ringing could the real limiter. Fourteen stub nodes each present an impedance discontinuity, producing reflections and ringing 5. The critical mechanism:

    • Ringing typically appears predominantly on the dominant-to-recessive edge, because a standard CAN-FD driver's output impedance rises to roughly 60 kΩ in recessive state — a severe mismatch against the ~60 Ω bus, so reflections are not absorbed 5.
    • At 2 Mbps (500 ns bit) there is ample time for reflections to decay before the sample point. At 5–8 Mbps (200 / 125 ns bits), settling time becomes comparable to the bit time, and recessive bits may still be ringing when sampled.
    • With 14 discontinuities on a 50 cm trace, reflections overlap rather than decay individually — this is why the guidance for high-node-count or long networks is typically to reduce the data-phase rate 4.

    3. Transceiver (3.3 V VCC): both TCAN3403-Q1 and TCAN3404-Q1 should suffice. I.e. at 3.3 V, the transceiver still meets the CAN requirement for ≥ 1.5 V differential output, and 3.3 V and 5 V CAN transceivers interoperate on the same bus 8.

    Termination: one 120 Ω resistor at each physical bus end (60 Ω total differential load) 9. Split termination — two 60 Ω resistors with a center capacitor to ground — improves high-frequency common-mode noise behavior 10. Keep the stub to each terminating node as short as possible 11.

    Protection: two-channel bidirectional TVS between transceiver and connector. ESD2CAN24-Q1 provides ±24 V working voltage, ±30 kV IEC 61000-4-2 ESD, 3 pF capacitance; ESD2CANXL24-Q1 offers 1.7 pF 12. Choose the lower-capacitance part — with 14 nodes, per-node parasitic capacitance accumulates directly against your edge rates.

    Routing:
    - Linear trunk, termination at both ends, minimal stubs; avoid star topologies 13
    - Place TVS and filtering close to the bus connector, keeping protection components in the signal-current path 14
    - Decoupling close to VCC / VIO; use at least two vias for bypass and protection connections to minimize inductance 14

    Bit timing: Confirm with the controller's team but typically calculated from the controller clock and may apply identically at every node:

    • bit rate = f_CAN / (BRP × (1 + TSEG1 + TSEG2))
    • sample point = (1 + TSEG1) / (1 + TSEG1 + TSEG2)

    Verify against your MCU's reference manual 15. Match the sample point across all 14 nodes; a late sample point gives more settling time for reflections but reduces propagation-delay tolerance, thanks.

    1. TCAN3403-Q1 Datasheet (p.10)
    2. TCAN3403-Q1 Datasheet (p.1)
    3. TCAN3403-Q1 Datasheet (p.26)
    4. E2E: TCAN1145-Q1 GB7220 standard
    5. SIC Transceiver Datasheet (p.29)
    6. TCAN3403-Q1 Product Parameters
    7. SLLA636A: 3.3 V CAN Transceivers (p.5)
    8. SLLA337A: 3.3 V CAN Interoperability (p.2)
    9. E2E: TCAN3403-Q1 circuit review
    10. Datasheet SLLSFS8A (p.24)
    11. E2E: TCAN3403-Q1 schematic review
    12. E2E FAQ: ESD2CAN24-Q1 CAN ESD protection
    13. E2E: TCAN1044-Q1 CAN bus use case check
    14. Datasheet SLLSFX3B (p.24)
    15. E2E FAQ: MCAN external transceiver bit timing

    Best Regards,

    Michael.