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TCAN1043A-Q1: oscillations of CANH and CANL after Common mode choke.

Colt Zhang
Expert 5490 points

Part Number: TCAN1043A-Q1

hi  team,

The customer detects the CANH and CANL waveforms inconsistently before and after the common mode choke, there is a noticeable oscillation after the common mode choke, the customer attempts to remove the common mode choke, directly shorting the pad, Waveforms have improved but oscillations still occur .

scope2: after the common mode choke 

scope 3: Remove the common mode choke 

the PCB and schematic is  as follow:

TCAN1043A SCH_PCB Review.rarSCH_CAN_8316_5155.pdf

  • 0
    TI__Mastermind 26836 points

    Colt,

    We have an application note (LINK) that can help explain the impacts of common-mode chokes in CAN networks. These chokes are not needed for networks to operate, though they can be used if desired. The application note highlights some of the risks that can arise from implementing common-mode chokes as shown in your schematic.

    Generally, ringing is an artifact of capacitance, but this does not appear to be caused by the transceiver. It looks like some common-mode noise is being injected onto the CANH/CANL lines from elsewhere on the PCB. I would measure other switching/digital signals nearby to see if any of those signals are switching at the moments where transient voltage changes are seen on the waveform. This could help narrow down the cause of these spikes.

    Best,

    Danny