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SN65HVD234-Q1: Can not get Transceiver to function.

David Cochlin
Prodigy 10 points
Part Number: SN65HVD234-Q1

Thanks in advance for any help. 

I just created a new design using the 3.3v transceiver coupled with an MCP2515.

Everything works fine with the MCP2551 (at 5 volts) with the MCP2515 at 3.3v on the bench. 

My new design doesn't have 5v which is why I ordered this chip. I swap them out changing the rail voltage to 3.3v which what the is MCP 2515 is using (yet it doesn't function). 

My current wiring for Both chips (On bread board before I waste my circuit boards) is:

Pin 1 - TXD
Pin 2 - GND
Pin 3 - 3.3v  (5 volt when using MCP2551)
Pin 4-  RXD
Pin 5 - 3.3v
Pin 6 - CAN L
Pin 7 - CAN H
Pin 8 - GND

I have checked voltages while running and getting 3.2 volts. When I swap back MCP and change rail to 5v it works fine. So I don't think there is any issue with the other connections. 

There are no other resistors hooked up at the moment other then 120 ohm between CANH and CANL

I'm verifying output with a Kvaser Leaf CAN sniffer. 

Am I missing something? I thought this chip would be a direct swap for the MCP with the exception of voltage. 

I've also tried 2 different new transceivers with same results. 

Please help... 

David

  • 0
    TI__Guru 62920 points
    Hi David,

    Your understanding of the HVD234 functionality is correct, and the connections that you described should be OK. To debug this, would you be able to probe some of the signals with an oscilloscope? It would be interesting to take a look at the TXD inputs to make sure it is valid, then make sure the CANH and CANL signals are behaving as expected (i.e., outputting dominant and recessive levels corresponding to the logic state on TXD). Then, you could verify that the RXD output is properly reflecting the CANH/CANL inputs of the transceiver. That may help narrow things down a little more.

    One other suggestion would be to check into the termination used. You mentioned 120 Ohms between CANH and CANL, but is there termination in the CAN sniffer as well? Ideally the equivalent resistance between CANH and CANL would be 60 Ohms (since CAN buses are designed to be terminated with a 120-Ohm resistor on either end, and these resistances act in parallel). The termination resistance value can influence both the signal levels and the transition timing, and so if you are using a single resistance only you may want to switch it to 60 Ohms at the moment (or connect another 120-Ohm resistance across CANH/CANL).

    Regards,
    Max
  • 0 in reply to Miguel Robertson
    TI__Guru 62920 points
    Hi David,

    I wanted to check back in on this. Have you had any luck in debugging this issue?

    Max