Dear team,
our customer is facing a temperature issue with the SN65HVD234 at could temp. Attached please find an explanation as a starting point. I also received measurements that I can send offline. Here is the description of the behavior:
We are doing final thermal qualification of a new product before it's release for sale and we are experiencing a CAN bus issue that we don't understand. Our product is using CAN bus on the backplane with termination at the ends. The backplane is short (less then 1 meter) and running transmission lines on multi-layer PCBs.
The CAN network under test has one manager and 12 devices so it's a small network.
The problem seems to occur at cold temperatures around -40C although it's not an absolute trip point. The system has run as cold as -60C and appears to be stable.
The system under test has one particular card plugged into the backplane that appears to cause CAN bus failures with its immediate neighbor although there are multiple cards plugged into the network that are not directly affected.
The symptom causing a problem on the CAN network is a bad acknowledge bit. The neighbor of the suspected card sends out a response to a message from the backplane manager, but the acknowledge signal does not drop correctly and remains high too long. As a result, the bad acknowledge results in the CAN controller's auto-retry mechanism kicking in and flooding the networks with repeated messages. The CAN controller is part of the STM32F105 MCU.
We suspect there is one specific card that is causing the issue because when we remove the suspected card the bad ACK no longer occurs on the neighboring device. However, if it is true that one device is causing problems with a direct neighbor, it is strange that there is no bad ACK on any other module on the network.
We have to release this product ASAP so any assistance you can provide to help us resolve this is greatly appreciated. Let us know if it would help to do a conference call or webex to provide further explanation.
Pleas advice how to proceed!
Lutz