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Original question:

SN65HVD256: Application issues

SN65HVD256: SN65HVD256DR can h and can l have noise when the environment temperature decrease 5℃ or less ?what may cause that?

zhuo yuan
Prodigy 30 points

Part Number: SN65HVD256

SN65HVD256DR  can h and can l have noise when the environment temperature decrease 5℃ or less ?

the CAN communication link (waveform captured by a logic analyzer) shows noise roughly every 6–7 seconds. 

what may cause that?

  • 0
    TI__Guru 70607 points

    Hi Zhuo,

    This is typically due to the bus topologies. I.e., termination / biasing should be for an effective impedance of 60 ohms and may have deviated due to temp change. Also ensure no extra or long stubs / star topologies, supply / GND shifts. Ensure the ECU is not waking every few seconds causing current steps by observing the power rails at the iC and MCU side to compare. May ensure sufficient decoupling caps if any dips.

    May also disconnect all nodes / components  connected to the IC one by one to help isolate which is more sensitive ti the temp decrease, thanks.

    Best Regards,

    Michael.

  • 0 in reply to Michael Ikwuyum
    Prodigy 30 points

    termination resistance is 60 ohm. I have tested it ,the noise is still when the temperature is low(5℃ or less).  I have tested the power rails of this IC,the 5V didn't have obvious change when the noise occurs. the MCU seems OK and the can waveform is like this. I have stop other nodes (remove U96 and U97

    SN65HVD256DR from PCBA.) P24 didn't connect any node. but the issue is still. the schematic is shown as the following. can you help analyze?

    )

  • 0 in reply to zhuo yuan
    TI__Guru 70607 points

    Hi Zhuo,

    Could you confirm every thing connected to the device is disconnected / depopulated and the CANH / CANL is observing the noise when only the TXD input is toggling? 

    Best Regards,

    Michael.

  • 0 in reply to Michael Ikwuyum
    Prodigy 30 points

    hi Michael

    yes, has removed all can nodes,CAN h and can l still has noise. I have tested canh and RXD signal,the test result is shown as the following.

    please help analyze ,thanks very much.

    best regards

    Zhuo Yuan

  • 0 in reply to zhuo yuan
    TI__Guru 70607 points

    Hi Zhuo,

    By everything, I am also referring to resistors, capacitors, diodes etc. Could you help confirm? 

    For example, depopulate the 0 ohms resistor on CANH and CANL then probe the IC pin of that particular IC to confirm, thanks.

    Best Regards,

    Michael.

  • 0 in reply to Michael Ikwuyum
    Prodigy 30 points

    OK, I will test it.because it is APQP boards,  for one of the issues boards, I have found the noise source, it come from one unused node, when the temperature become low , the pin 1 of U96 has the noise ,which is shown as the following figure. so I pull up pin 8 to high(voltage) to disable the U96, For this PCBA it seems that the solution is OK. 

     

    but for the other PCBA , the solution it seems not OK. when the U96 is disabled(pull up pin 8 to high(voltage)) , the noise is still. can you help analysis?

    best regards

    zhuo

  • 0 in reply to zhuo yuan
    TI__Guru 70607 points

    Hi Zhuo,

    It would seem the noise is coming from the supply and would recommend ensuring sufficient decoupling capacitors are included as close as possible to the IC pin to double confirm, thanks.

    Best Regards,

    Michael.