• State TI Thinks Resolved
  • Locked Locked
  • Replies 1 reply
  • Answers 1 answer
  • Subscribers 33 subscribers
  • Views 258 views
  • Users 0 members are here
Support feedback
Options
Options
Related

This thread has been locked.

If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.

TCAN1044-Q1: TCAN1044-Q1, TCAN1462/3-Q1: Layout regarding transimpedance

Zena Lee
Intellectual 2740 points
Part Number: TCAN1044-Q1

Hi,

I got an request from customer asking for TCAN1044-Q1 and TCAN1462/3-Q1 layout guidance. The layout guidance is provided in the datasheet, but what customer asked was regarding transimpedance, considering interface type.

Could I get an feedback on layout in aspect of transimpedance?

Also, I'm not certain of what transimpedance means technically, could I get a comment on this too?

Thank you. 

  • 0
    TI__Genius 15345 points

    Hi Zena,

    Transimpedance is interesting concept that essentially is a relationship between current and voltage. When you apply a current as an input and receive a voltage as an output the relationship of current to voltage is transimpedance. The device that converts this current to a voltage almost acts like a resistor or an impedance load. That is where I believe the name comes from.

    In this case I think the customer is specifically asking how they can route a differential pair of signals in the most optimal. Here are some tips that will help with routing:

    First, if there is a common mode choke (CMC) that should be placed as close to the CANH and CANL pins as possible, then the termination resistors should be placed as close to the CMC as possible. If there is no CMC then the termination resistors should be placed as close to the CANH and CANL pins as possible. Next, make sure that you differentially route the CANH and CANL lines. It is important that they are as equal in length as possible. Make sure to keep the CANH and CANL signals close to each other. You want any noise on the bus to couple equally onto both lines.

    When it comes to protection devices, like a TVS diode, make sure they are close and along the signal path.

    Lastly, I recommend keeping your digital signals and other noisy lines away from the CAN bus. CAN messages can be decently fast and you don't want that noise to couple onto sensitive digital lines. On a multilayer board I would recommend making a copper pour of VCC or GND on the layer directly under the bus. This will help shield the layers below the bus from any noise.

    Best,

    Chris