CAN chip with no termination resistors MAX13052.

[cupoftea]

Hi,
I have been given a schem to layout with a MAX13052 CAN chip......it takes its TX and RX inputs from the circuit, and its right next to a connector, to which the 2 CAN outputs are connected....but the only peripheral components are a 33k connected to RS pin, and a 100nF cap connected to Vcc......do we need the 60R res and the 4n7 seen at page 18 of the MAX13052 datasheet?

MAX13052 CAN transceiver.

https://www.analog.com/media/en/technical-documentation/data-sheets/MAX13050-MAX13054.pdf

Also, i dont see any pullups on the TX and RX lines.....and they cant be inside of a micro since its receiving from a micro via a digi isolator....should there be pullups?

 

[FvM]

CAN is party line bus with end termination, it's not necessarily inside the node, but must be present at the bus ends. Low speed CAN may use higher termination resistors than 120 ohm.

Digital isolators have usually push-pull outputs, why pullups?

 

[cupoftea]

Thanks, sorry, the TX and RX come from a connector which comes down from a LCD board...i dont have the schem for that....maybe there are pullups there......but surely you would want the pull ups near the CAN chip?

 

[prairiedog]

Short-haul CAN within a product you can get away with a lot, it depends on speed and length of the stub. Is the bias split and termination done at least on the other end?
If you're doing a PC board design, just leave a provision for termination resistors and a "do not populate" directive. Then there is no cost but a little coverage just in case. Termination resistors due waste a lot of power, if current consumption is a concern.
Note automotive applications always use a CM choke on CAN to keep EMI low.