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LTC6804-2 PEC error next to a high voltage motor inverter

Hello,

I am developing BMS slave devices based on the LTC6804-2 IC. I put the BMS salves into an electic vehicle and when the 3 phase motor inverter starts to work it causes a lots of PEC errors on the isoSPI bus. When the motor inverter is not working i got no CRC errors. I think the inverter operation make some noise on the isoSPI bus. I put to the same environment the DC1942CFA eval board and then i got no PEC errors. My suggestion is that there is some board design difference between the two boards because the components of the two boards basically are the same. Could you please give me some advice about the design to make it more EMI protected or some ideas what things should i change to get rid of the issue? I attached the BMS salve board 3d picture.

Thank you very much,

Richard

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  • Presumably the LTC6820 circuit has the same termination and the live bus is resistively terminated at each endpoint, so aside from layout differences Its hard to say why the demos work better. It may be that the ground plane should remain away from the cell contacts and area beyond the IC side of the CMC to maximize RF decoupling.

    Even though the -2 demos may seem to work ok, I would suggest you consider tweaking the design to use the -1 part instead, as the noise performance will be far better and you wont need the dip switches. The transformer and CMC can be replaced by an HM2113ZNL for proper HV isolation (while the hipot of 68386 is 1.5kV, the long-term rating on these is <60V according to the insulation grade, now these better parts have come along with the proper Teflon insulation). If the secondary port is not exposed to personnel (for safety) then only a CMC is needed on that one, as the HV separation would occur on the next board. While the daisy-chain would seem less reliable, the data integrity is much better due to the limited extent of the inter-IC wiring plus the better pulse fidelity of point-point regenerated links.

  • I have solved the issue. The problem was that the isolation transformer (PE-68386) collected noises which causes CRC errors on the bus. I replaced with H1102FNL and then everything is fine.

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