SN65HVD233-HT: CAN signal has high spikes at 500Kbps

Jian Chen94

Part Number: SN65HVD233-HT
Other Parts Discussed in Thread: SN65HVD233

Hi,

I am connecting my PCB board to a USB-CAN adaptor on my PC. My PCB uses SM470R1B1M as mciro and SN65HVD233 as CAN transceiver.

When I set CAN transfer speed at 500Kbps, I see the hugh spike at the end of transfer at CANL line. This causes my firmware stop functioning.

If I set to 1Mbps, then the signal is fine.

I have 120 ohm resistor connected between pin 6 and 7 of SN65HVD233.

What is the problem?

Thanks, Jian

over 8 years ago

0 Christian Yots over 8 years ago

TI__Genius 14540 points

Hi,

I have assigned your inquiry to the engineer most knowledgeable with this device. He should be contacting you in the near future to assist.

Thank you,
Christian

0 Wade Vonbergen over 8 years ago in reply to Christian Yots

TI__Guru 62930 points

Jian,
This is very unusual. The spike you are showing is about 9V.
There is nothing on the SM470R1B1M that can generate this voltage.
Can you provide schematic? Is it simply a connection from the R1B1M to the HVD233?
Do you have 120ohm termination on each end of the bus?
Have you captured a more precise scope shot of the spike?

Regards,
Wade

0 Jian Chen94 over 8 years ago in reply to Wade Vonbergen

Intellectual 505 points

Wade,

Please see the attached for schematic. The micro is SM470, not TMS470 as shown.

I put a 120 ohm resistor between Pin 6 and pin7 of SN65HVD233. I don't have termination resistor on the USB-CAN adaptor side where I send and receive message from PC.

If I use 1Mbps, everything is fine. Only has spikes at 500Kbps.

Thanks, Jian

0 Jian Chen94 over 8 years ago in reply to Jian Chen94

Intellectual 505 points

I attach schematic here. For some reason, it does not allow me to paste Snipping Tool image. Let me know if you can see the image.

0 Wade Vonbergen over 8 years ago in reply to Jian Chen94

TI__Guru 62930 points

Jian, it did not come through.

To include an image, you select the "Use rich formatting" option on bottom left.

Then select the paperclip "insert file"

Regards,

Wade

0 Jian Chen94 over 8 years ago in reply to Wade Vonbergen

Intellectual 505 points

can.docx

0 Wade Vonbergen over 8 years ago in reply to Jian Chen94

TI__Guru 62930 points

Jian,
This document does not show any termination. If there are only 2 nodes on the bus, then there should be a 120 ohm resistor on each end of the bus.
Please also include a scope shot of the spike zoomed in closer.
It would also be worthwhile to probe power at the same time. Possibly there is event on the power supply?
Regards,
Wade

0 Wade Vonbergen over 8 years ago in reply to Wade Vonbergen

TI__Guru 62930 points

Jian,
Were you able to get improved results? If so, please indicate solution.
If this resolved your issue, please click "This Resolved My Issue" on the forum.
Thank you.
Wade

0 Jian Chen94 over 8 years ago in reply to Wade Vonbergen

Intellectual 505 points

Not yet. We are waiting for the communication between 2 boards to be tested.

0 Wade Vonbergen over 8 years ago in reply to Jian Chen94

TI__Guru 62930 points

Jian,
Have you resolved the issue?
If so, please let us know and click "This Resolved My Issue"
Thanks,
Wade

0 Jian Chen94 over 8 years ago in reply to Wade Vonbergen

Intellectual 505 points

Wade,

Unfortunately, we are not testing the boards until the early next year.

After we finish, we will let you know.

Thanks, Jian

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SN65HVD233-HT: CAN signal has high spikes at 500Kbps