CAN Bus Protection circuit

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#1
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Hi there,

We are on the design state of CAN bus product using the PCA82C251 transceiver from Philips. We have used an external circuit for the transceiver protection, but we finally realised that it is not protects the ic.
We found another ic from ST (L9615) that is pin to pin compadible with the one from Philips and also supports short circuit protection.

Our problem here is what to do with the products that have the PCA82C251 soldered on board. We have SMB pads (for protection diodes) at the ic's CanH and CanL pins and after them we have MicroSMD-1206 pads in series (for low current polyswitches) from both CanH and CanL pins to the external connectors.

We analised the protection circuit and we found that the 50mA/4Ohm polyswitches that we use are too slow (0.35 - 1.5sec) to protect the ic.

Is there any idea for what to do to protect the current production?

Thank you.

Michael.

User of:
IAR Embedded Workbench C/C++ Compiler
Altium Designer

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What exactly are you trying to protect the IC from? The datasheet mentions that it is protected against shorts to ground and +24V. Seems like it's already pretty well protected.

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If you limit your CAN baud to 125 kbps maximum there are transceiver chips that do +-60 volts, short circuit, over temperature, etc. protection. There are others that are not PCA82C251 pin compatible that will do 1 mbps with +-80 volt protection. Take a look at MC AN228:
http://www.microchip.com/stellen...

I understand you are in a bad spot. If its not too many units, maybe you can rework them with new chips and just take the loss? If the old ones are really in danger of failing in the field, warranty repair is allot more expensive and your reputation takes a big hit as well.

There are other protection technologies, but you are limited by bus propagation delay times, it must be bidirectional and I doubt you will find anything that is also existing PC board pin compatible. Maybe you could make something that connects at your PCB CAN bus connector, then to the CAN bus and adds external protection?

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Guys thanks for your time and I really appreciate your suggestions. I am sorry, because I might do some tests before posting.

So please, don't waste your time reading this post anymore. I will finish my research and I will probably post again.

Thank you all.

Michael.

User of:
IAR Embedded Workbench C/C++ Compiler
Altium Designer