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TCAN1042V-Q1: TCAN1042V-Q1 Failure case root cause analysis

Part Number: TCAN1042V-Q1

Hello,

One of our battery management systems which uses TCAN1042V-Q1, had a failure case in which we saw that VIO-GND has a resistance of 1 ohm, CANH-GND has a resistance of 22kohm. All other pins are coming as open when disconnected from the circuit and no power is given to the IC. Rest all parts which are connected in parallel to VIO-GND are working OK, only part affected is the CAN IC. Schematic used is attached (Please ignore the minor mistakes in pin naming), CANH, CANL, GND goes onto the connector.

Can you please tell us what could have caused such failure? Please let us know if you have any other question. The failure occurred on a running vehicle.

  • Shyama,

    First, your schematic looks correct except that VIO should have a decoupling capacitor of 100nF just like the VCC pin.

    Typically when we see a low impedance path created on one of the CANH or CANL pins, this would point to a high-voltage transient occurring on the CAN bus and damaging the CAN bus stack which is referenced to VCC. With the damage on VIO, this is not something that is typically seen from a voltage transient on the CAN bus. What else is the 3.3V supply connected to in this system? And is the device still function when power is applied, or is the VIO not able to be supplied because of the low-impedance path to GND on the pin?

    Regards,

    Eric Hackett 

  • It is connected to Microcontroller. The VIO and the supply for uC goes to 0V as soon as 3.3V is connected to from an onboard generated power supply (It is current limited to 1A). How can we protect the CANH, CANL from high voltage transient?

  • Shyama,

    The D7 diode should be protecting the CAN bus from transients if it is specified correctly. What is the part number for this diode?

    Understood about the VIO pulling the supply to GND, that's what I suspected, so this device is not able to be used anymore. Are there any high voltages that the CAN bus pins are being exposed to, like a battery supply or anything else?

    Regards,

    Eric Hackett 

  • D7: CDSOT23-T24CAN. It is bundled into a harness which might have some high voltage wires, I'll check for that.

  • We have another case where both VCC-GND and VIO-GND goes to below 10 ohms resistance along with CANL-GND being 33kohm. Can you recommend the right harness design for a system with 4 CAN nodes?

    We don't have R18, R19 populated since there are other 2 nodes have CAN terminating resistor and our BMS along with another device have NO CAN terminating resistor. We don't have a specific reason to not populate C6, C7 neither are we using Csplit generally connected between R18, R19 and GND. 

    Can such transient affect VIO, VCC pin reliability too? I'll verify the harness. Please let us know regarding relevant uses of capacitors in any places to suppress any transient and what is the typical source of such transients to rightly size these capacitors?

  • Shyama,

    Yes, please let me know. And the diode should work for protecting the CAN bus, transients can still sometimes get through and damage the pins though. Is there any reason the capacitors on both CANH and CANL have been depopulated? These are typically just used for high-frequency noise filtering, but could help with transients by slowing down the rising edge.

    Also, how many devices have shown this same type of failure signature?

    Regards,

    Eric Hackett 

  • Shyama,

    Yes, I would expect the VCC structure to be affected by a CAN bus transient more often than the VIO structure. So in both cases, this along with the damage on the CAN bus pins seems to point to some kind of transient on the bus causing EOS damage. The path from CAN bus to VCC is very clear since the CAN bus receiver and transmitter are both referenced to VCC, however the VIO path is not totally clear. That being said, damage to VIO as a result of a CAN bus transient is not unheard of, just much less likely than VCC.

    In terms of a harness recommendation, can you give more details about the system? I know there are 4 nodes, but is there a size/shape constraint? The best and most straightforward is the standard bus topology used in any communication bus, but if there are more constraints in the customer system please let me know.

    Regards,

    Eric Hackett