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SN65HVD234: Please tell us about CAN Termination Resister

Munekazu Sugimoto
Prodigy 100 points
Part Number: SN65HVD234

Hi

Our system using  SN65HVD234D for CAN communication .

But we have some isseus  CAN communication.

This is our TEST result

1)   System  Side  SN65HVD234D ( Termination Resister 120ohm )   ==== >   CAN  Device  (  Termination Resister 120ohm  )

  =>  This is CAN Communication is OK

2)  System  Side  SN65HVD234D ( Termination Resister 120ohm )   ==>   CAN  Device 1 (  Termination Resister 120ohm  )   =>> CAN  Device 2 (  Termination Resister 120ohm  ) 

    => Yes  ,  Our System Connect  two CAN device with  2 each Termiantion Resister  ( 120ohm x 2)

【Question】

   Sorry...I did not  know detail for CAN  interface spec.

   Is it correct  for our this CAN Connect  system  (   MCU: 120ohm , CAN Deivice 1 :120ohm , CAN Device 2 :120ohm) ??

Regard

 March Jasper  ( In Japan )

 

                                                             

  • 0
    TI__Guru 67242 points

    March,

    Thanks for bringing this question to E2E. On a CAN bus, only two end nodes need the 120 ohm termination presentation. Adding a third 120 ohm termination resistor will drive down the overall bus impedance to 40 ohms, when the CAN bus driver is specified to drive at least 1.5V over a 60 ohm load.

    Regards,

    Eric Hackett

  • 0 in reply to Eric Hackett
    Prodigy 100 points

    Hi  Erick 

     Thank you very much this quick replay.

    I have one question for aboit this CAN Terimiantion questuon . 

    If we have 3 termination with same Bus Line,   what happen ?? 

    For Instance 

       Many error appear ??

      Signal  Level change to low ??

     

    Yes, we have many CAN data error when 3 termination connected. 

    Regard

    Jasper  

  • +1 in reply to Munekazu Sugimoto
    TI__Guru 67242 points

    Jasper,

    With three 120 ohm termination resistors, that brings the bus impedance down to 40 ohms. CAN bus drivers are designed to drive a 60 ohm bus, and with a 40 ohm bus, the CANH and CANL waveforms will be attenuated and much more susceptible to external noise. With the attenuation, the differential will also be attenuated, and thus the received signal may not meet the dominant thresholds, which is likely why you're seeing errors.

    Regards,

    Eric Hackett