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  • TI Thinks Resolved

TCAN1042-Q1: CANH and CANL low resistance w.r.t GND

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Replies: 1

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Part Number: TCAN1042-Q1

Hii 

I was using the TCAN1042 IC in one of my application. Recently we found that in 3 PCBA's CANH and CANL are showing low resistance w.r.t ground(in ohm). we have TVS diodes(SZNUP2105LT1G) on CANH and CANL lines(placed near to connector). Also we have common mode choke(ACT45B-220-2P-TL003). when i measure the TVS it is healthy. when I replaced the CAN IC system working fine. I need to understand at what situation this problem will occurs.  

1) Power supply to IC cannot go more than 5.3V. if it goes above uC will shunt down the system.

2)  I have checked the placement of TVS. it is near to connector and differential lines are taken care such that if any surge comes TVS will react.

Can I know at what are all condition this problem can occur

Also can i get the document which i mentioned in the below comments

Hi Mitchell,

Unfortunately I don't, and because of some weather-related issues with our lab at the moment I'm not able to capture these (the other waveforms I had on hand already).  I can tell you that if CANH is shorted to CANL, the differential voltage between them will be 0 V and the receiver will only report a recessive state on the bus.

If you think through the different possible shorting scenarios, you can predict the device behavior based on its performance as documented in the datasheet.  Understanding the behavior of the device in this way is better in my opinion that trusting in the results of a single measurement (with its assumptions related to battery voltages, other nodes on the bus, shorting impedances, etc.).  I've put together a document that describes how a transceiver would behave under different system-level fault conditions.  I will send it to you via e-mail, and hopefully that can be used to give some better confidence in the part.

Regards,
Max

Regards

Bharath Gilla

  • Bharath,

    This failure signature is typically the result of a high-voltage transient occurring at the bus pins, and while the TVS diode should protect the transceiver from damage, there are a couple of things that could be happening to still allow the transient voltage to damage the pins.

    1. The transient could be large enough that the TVS clamping voltage exceeds the transceiver rating.
    2. The common-mode choke could be causing a kick-back transient to the pins as a result of the initial transient spiking the voltage level on the CAN bus pins.

    We had a call and are discussing this through email and it was explained that this damage must have occurred between assembling the CAN transceiver to the module and then testing the module before it goes into the full application. If that's the case, the assembly process should be monitored to verify that there are no transient or ESD events that could be occurring to cause this kind of damage. 

    Please let me know if you have any other questions.

    Regards,

    Eric Hackett

    Texas Instruments | INT-TRX| Applications Engineer

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