TCAN4551-Q1: ringing and overshooting on the CANH and CANL

Hello Omar,

Looking at the plot it appears that CANL is the Top Waveform (White) labeled A0 and CANH is the Bottom Waveform (Orange) labeled A1.  Is that correct?  If so, then the ringing is on Dominant-to-Recessive transition. 

The transceiver actively drives the Dominant voltage levels and becomes passive during the Recessive bits allowing the termination resistors to pull down the lines to the recessive voltage levels.  Different wiring harness architectures, termination placement, number of total CAN nodes and their placement on the bus will all impact the signal integrity of the CAN bus.  I assume these signals were not captured while the device was connected to a full bus, but if so, any number of factors could cause them.  However, these little overshoots would not impact the CAN data sampling in any way.

These overshoots could also be from inductance in the scope probe connection and the GND connection and I have seen similar or worse overshoots from probes in the past.  You may want to ensure that the probes are well grounded near the location where the CANH and CANL signals are being probed.  

Adding capacitance to the bus should help reduce these overshoots by adding additional filtering and slow down the transition edge.

Regards,

Jonathan

Hi Jonathan,
Yes. White is CANL and Orange is CANH.
This was done to query the VIN on an OZEN simulator. so it wasn't full on communication.

Regards,
Omar

Hi Omar,

Thank you for confirming the CANH and CANL signals.

Regards,

Jonathan