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SN65HVDA1040A-Q1: CAN Driver TVS diode maximum Clamping voltage and Junction Capacitance

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Part Number: SN65HVDA1040A-Q1

We are using SN65HVDA1040A-Q1 with maximum data rate of 1Mbps. At bus terminals(CANH, CANL) we are using SMAJ24CA-E3 TVS diodes for protection. This diode have maximum clamping voltage of 39.8 V and Junction Capacitance above 2000pF to 3000pF.

1. The CAN Driver support maximum -27 V to 40 V Voltage on bus terminals(CANH, CANL).  So is there any problem in negative transient as maximum voltage is -27 V and clamping voltage is -39.8V.

2. The CAN driver is operating at 1Mbps, Is there any problem due to diode Junction Capacitance (2000pF to 3000pF).

3.  Also let me know typical Capacitor value in Split Termination

  • Arvind,

    1. Yes, this may present issues with the delta in the absolute maximum rating and the clamping of the diode. The device pin will likely be damaged in the event of a negative transient greater than -27V, so the diode clamping at -40V won't help.
    2. This much capacitance added will distort the waveform but at 1Mbps the communication should still be okay. The problem is you're going to be severely limited on added capacitance on the rest of the CAN bus. I looked up this diode's datasheet and it looks like the junction capacitance is around 200-250pF, not 2000pF. Where was the 2000-3000pF value found?
    3. Typical capacitor value for SPLIT capacitance is 4.7nF, but it range from 4.7nF to 100nF. 

    Is there a particular reason the SN65HVDA1040A-Q1 was chosen? The TCAN1042-Q1 has the same pinout (minus the SPLIT pin, which isn't necessary for the TCAN1042), higher absolute maximum ratings on the CAN bus pins, higher ESD protection, and several other benefits. 

    Also, if you wanted to look into a TVS diode that had the same clamping voltage but lower capacitance, PESD1CAN is typically recommended.

    Regards,

    Eric Hackett

    Texas Instruments | INT-TRX| Applications Engineer

  • In reply to Eric Hackett:

    Thank you Eric for replay.

    Yes it is 250pF to 300pF. I will check possibility TCAN1042-Q1 and PESD1CAN.

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