TLIN2021A-Q1: TLIN2021A-Q1 Termination of INH pin for floating INH pin.

• Placement: Place a ferrite bead and capacitors close to the LIN pin of the TLIN2021.
• Component arrangement:
  • Add a ferrite bead in series with the LIN trace.
  • Connect a small capacitor (e.g., a 100 pF ceramic capacitor) from the LIN trace to ground on the device side of the ferrite bead. This will help with high-frequency filtering and ESD protection.

Hi Manoj,

Please see my feedback below:

• Remove one of the pullup resistors on the LIN bus. The LIN standard says the commander node should only have 1k Ohm pullup resistance.
• I would recommend replacing SZNUP1105 with a 36 V TVS diode like TSD36C-Q1 if you plan on using this for 24 V applications.
• I would NOT reccomend adding 100 nF capacitors to the bus as Sunilbhai suggested earlier. The max allowable capacitance on a LIN bus is 10 nF, so 100 nF will cause issues. 

Outside of that everything else looks good. 

Regards,

Matt 

Corrected Recommendation:

• Ferrite Bead: Place a ferrite bead (e.g., BLM21PG221SN1, 220 Ω at 100 MHz) in series with the TLIN2021A-Q1 LIN pin, close to the pin (<1 cm), to suppress EMI.
• Capacitor: Use a 100 pF (not 100 nF) ceramic capacitor from the LIN pin to ground on the device side of the ferrite bead for high-frequency filtering and ESD protection.
• LIN Pull-Up: Ensure a single 1 kΩ pull-up to VSUP at the commander node, removing extras.
• TVS Diode: Use a 36 V TVS diode (e.g., TSD36C-Q1) for 24 V applications.
• Test: Verify LIN bus signal integrity (rise/fall times <5 µs) with an oscilloscope.                                                                                                                         

  LIN Bus Context

  • LIN Bus Characteristics:
    • Data rate: Up to 20 kbps (50 µs bit time).
    • Maximum bus capacitance: 10 nF (per ISO 17987) to maintain signal rise/fall times (<5 µs).
    • Typical bus impedance: Includes a 1 kΩ pull-up resistor at the commander node and the bus’s parasitic capacitance (from wiring, nodes, etc.).
    • The TLIN2021A-Q1 LIN pin interfaces with a single-wire bus, and external filtering must suppress EMI (e.g., >100 kHz from automotive noise sources) while preserving signal timing.
  • Purpose of 100 pF Capacitor: Placed from the LIN pin to ground (after a ferrite bead), it filters high-frequency noise (e.g., EMI from switching components) and enhances ESD protection, as recommended in my corrected advice.

  Calculation

  1. Impact on Bus Capacitance:
     • The LIN specification allows a total bus capacitance of 10 nF (10,000 pF). This includes contributions from all nodes, wiring, and added components.
     • A 100 pF capacitor per node (e.g., at the TLIN2021A-Q1) is a small fraction of this limit: 100 pF10,000 pF=0.01 (1% of max capacitance)\frac{100 \, \text{pF}}{10,000 \, \text{pF}} = 0.01 \, (1\% \text{ of max capacitance})10,000pF100pF​=0.01(1% of max capacitance)
     • Even with multiple nodes (e.g., 4–8 sensors for reverse parking), the total added capacitance (e.g., 8 × 100 pF = 800 pF) remains well below 10 nF, leaving room for wiring parasitics (~1–2 nF typical).
  2. RC Time Constant with Pull-Up:
     • The LIN bus has a 1 kΩ pull-up resistor at the commander node. The time constant ($\tau$) for a 100 pF capacitor is: $$\tau =R\times C=1\text{k}\Omega \times 100\text{pF}=100\text{ns}$$
     • LIN signal rise/fall times must be <5 µs (10% of bit time at 20 kbps). The 100 ns time constant is negligible compared to 5 µs: 100 ns5 µs=0.02 (2% of max rise time)\frac{100 \, \text{ns}}{5 \, \text{µs}} = 0.02 \, (2\% \text{ of max rise time})5µs100ns​=0.02(2% of max rise time)
     • This ensures the 100 pF capacitor does not slow down signal edges enough to violate timing requirements.
  3. Filtering Effectiveness:
     • The 100 pF capacitor, paired with a ferrite bead (e.g., BLM21PG221SN1, 220 Ω at 100 MHz), forms a low-pass filter to suppress high-frequency EMI (e.g., >100 kHz from switching regulators or motors in your EV charger system).
     • Approximate cutoff frequency (fcf_cfc​) for the RC filter (using the ferrite bead’s resistance at high frequency, ~220 Ω at 100 MHz): fc=12πRC=12π×220 Ω×100×10−12 F≈7.23 MHzf_c = \frac{1}{2 \pi R C} = \frac{1}{2 \pi \times 220 \, \Omega \times 100 \times 10^{-12} \, \text{F}} \approx 7.23 \, \text{MHz}fc​=2πRC1​=2π×220Ω×100×10−12F1​≈7.23MHz
     • This cutoff effectively attenuates EMI above 7 MHz, well above the LIN bus’s 20 kHz signal bandwidth, while passing LIN signals cleanly. For lower-frequency EMI (e.g., 100 kHz), the ferrite bead’s impedance increases, enhancing suppression.
  4. Comparison to 100 nF (Incorrect Choice):
     • A 100 nF capacitor would yield: $$\tau =1\text{k}\Omega \times 100\text{nF}=100\text{µs}$$ This exceeds the 5 µs rise time limit, causing signal distortion and potential communication errors, confirming the other guide’s concern about violating the 10 nF limit (100 nF = 10× the max).

  Conclusion

  The 100 pF capacitor is appropriate because: (Iam very sorry for in previous post it was my mistake instead 100pf I had write 100nf.)

  • It contributes minimally to the 10 nF bus capacitance limit (1% per node).
  • Its 100 ns time constant preserves LIN signal timing (<5 µs rise/fall).
  • It effectively filters high-frequency EMI (>7 MHz) when paired with a ferrite bead, protecting the TLIN2021A-Q1 in your noisy automotive environment.

  Recommendation:

  • Place a 100 pF ceramic capacitor from the LIN pin to ground, after a ferrite bead (e.g., BLM21PG221SN1), close to the TLIN2021A-Q1 (<1 cm traces).
  • Verify total bus capacitance (nodes + wiring) remains <10 nF.
  • Test LIN bus signals with an oscilloscope to confirm clean edges and no errors during reverse parking sensor operation. I hope "aap ka Problem Solved HO Gaya Ho-Sunil from USA)