TCAN1463-Q1: BUS fault detection failure on CANL short to GND

Hi Lenny,

The bus fault detection works by measuring the differential current between CANH and CANL. When the current passes a certain threshold based on the fault type, the nFAULT pin will go low. In this case, since CANL to GND isn't a particularly abnormal condition, while still being considered a fault, the current may not be passing the threshold expected. The bus fault detection feature only works reliably for data rates of 400kbps or slower, can you try different data rates to see if nFAULT toggles low on TCAN1463-Q1?

Regards,

Sean

Hi Sean,

Thanks for your support.

BTW, any other suggestion to detect CANL S2G more than 400kbps?

Because TCAN1463-Q1 is used for CAN FD level up to 3Mbps as I guess.

Please let me have your feedback for it and other device to support it?

BR

Lenny Lee

Hi Lenny,

Lenny Lee said:

Customer found TCAN1463-Q1 can' t detect fault on CANL short to GND case as below, TCAN1043A-Q1 detect well but no fault on it with TCAN1463-Q1.

What is data rate of this testing above?

Their schematic looks good, if there any difference on PCB layout for TCAN1043A-Q1 & TCAN1463-Q1?

Regards,

Sean

Hi Sean,

Happy new year.

1. Customer said they've checked it under 500k, but customer is asking why TCA1043A-Q1 is working correctly and other 5 cases Bus fault detection is good for both devices.

2. I found both datasheet is saying Bus fault detection has to be greater Tcbf 2.5us, so we can say that it has to be under 400kbps?

3. Please let me know any other device can support bus fault detection over 500kbps condition?

BR

Lenny Lee

Hi Lenny,

Sorry I don't have a good explanation of why TCAN1043A-Q1 works but TCAN1463-Q1 not. Because CAN SIC have a different bus pin architecture, the current measurement are also different. We do not have any other device as a pin to pin alternation as their nFAULT works all the same, TCAN1145-Q1 has a more advanced bus fault detection feature but it's a device using SPI, there is no nFAULT pin on that device.

I'm trying to understand how their CAN bus circuits can affect the nFAULT toggle, do they have the same CAN bus layout of TCAN1043A-Q1 and TCAN1463-Q1 on the board? Right now the only difference we can notice on schematic is that bus filter capacitors. If they depopulate C601 and C603, will the test result change?

Regards,

Sean

Hi Sean,

Thanks for your feedback.

There're 2xTCAN1463-Q1 and 3xTCAN1043A-Q1 on same board and almost same layout(additionally 4xTCAN1044AV-Q1).

And they might not test without Cbus 7pF CAP, can we recommend to reduce it as TCAN1043A-Q1 circuit has as 3pF ?

Even if TCAN1043A-Q1 is working correctly over 400Kbps condition, I can say that we don't recommend to use the test result over 400kbps condition , just recommend to take the result under 400kbps condition?

BR

Lenny Lee

Hi Lenny,

Both devices should have the ability to work up to 1Mbps, but you are correct, to "reliably" reflect the bus fault on nFAULT, it is 400kbps.

Can you suggest them try to reduce those two capacitors to 3 pF or just depopulate them? 

Regards,

Sean

Hi Sean,

Thanks for your reply.

If TCAN1043A-Q1 is working well after changing CAP value to 3pF at each BUS lines, we can say that " Even if it would be good to work but we can't say that's not 100% Reliable" ?

It's little bit confuse, how can I say that to customer.

BR

Lenny Lee