SN65HVD230: SN65HVD230D: CANH CANL Wave is abnormal.

Cyan,

Thanks for bringing your questions to E2E. While 3.3V CAN transceivers are compatible with transceivers compliant to ISO11898-2, 3.3V CAN transceivers are not compliant with ISO11898-2 themselves. One of the main reasons is for what you've pointed out, the devices can't meet the recessive voltage level while simultaneously meeting the symmetry requirement.

Also, none of the images posted are showing on my side, is it possible to send them directly to my email? You can find it by clicking on my username.

Regards,

Some images were not uploaded successfully.  I will send them again.

"While 3.3V CAN transceivers are compatible with transceivers compliant to ISO11898-2, 3.3V CAN transceivers are not compliant with ISO11898-2 themselves."

-----I still can't understand the meaning of this sentence, could you elaborate on it.

Hi TI expert,

We are using SN65HVD230,  and here is some test results and we have some questions, please help to check.

Block:

Test 1: Vref connect to CANH, CANL via 3.3K resistance

CH1:CAN_H、CH2：CAN_L 、f1：CAN_H-CAN_L

dominant: CAN_H:2.8V CAN_L:1.0V

Recessive: CAN_H:1.8V CAN_L:1.8V

the question is:

1. By connecting the Vref  to CAN BUS via resistance, the Recessive level is pulled down to 1.8v, which is not consistent with the requirement of ISO11898 of 2.0-3.0v. Meanwhile, the datasheet describes typ2.3v and there's no  MIN and MAX value;

2. The MIN of dominant CANH in the manual is 2.45v, which is not matched with the 2.75v of ISO11898. The margin of 2.8v and 2.75v is very small.

3. From dominant to recessive, the waveform will have a slow process

4. However, ISO11898 requires vysm0.9 ~1.1, which is not satisfied here.

Test 2: Remove 3.3K resistance between Vref and CANH, CANL.

CH1:CAN_H、CH2：CAN_L 、f1：CAN_H-CAN_L

dominant: CAN_H:2.8V CAN_L:1.0V

Recessive: CAN_H:2.2V CAN_L:2.2V

Here are the questions:

1. Without connecting CAN BUS  to Vref via resistance, the Recessive level is 2.2v, which is consistent with the demand of ISO11898 from 2.0v to 3.0v

2. The MIN of dominant CANH is 2.45v, which is not matched with the 2.75v of ISO11898. The margin of 2.8v and 2.75v is very small

3. From dominant to recessive, there will be a slowing process in the waveform (different from test 1).

4. However, ISO11898 requires Vysm0.9 ~1.1, which is not satisfied here either.

5. Here, when CAN L changes from recessive to dominant, there is a return sulcus.

This problem has been bothering us for a long time and we hope to get your reply as soon as possible.Thank you very much.

Cyan

Hi Eric,

I have add the images above, could you please help to check it again?

Thanks.

Cyan

Hi Eric,

I have added images above. please help to check it, thanks very much.

Cyan

Thanks very much, Eric.

That's very clear.