• State Resolved
  • Locked Locked
  • Replies 7 replies
  • Answers 2 answers
  • Subscribers 34 subscribers
  • Views 999 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.

CAN transceiver SN65HVD233 output (R) at pin 4 when unpowered

Sheng Wang
Prodigy 250 points

Other Parts Discussed in Thread: SN65HVD233-EP, SN65HVD233

Hi there,

for CAN transceiver SN65HVD233-EP, If its pin CANH and CANL are driven normally by a separate board while the chip is not powered on its own board, does its output R (RXD) keep high impedance or stay at '0'?

Thanks

Sheng

 

  • 0
    TI__Guru** 103215 points
    Hello Sheng,

    With the device unpowered, the R output will remain high impedance regardless of activity on the CAN bus.

    Best Regards,
    Casey McCrea
  • 0 in reply to Casey McCrea
    Prodigy 250 points
    Thanks for your feedback, Casey.

    Based on the schematic (on page 18 of SN65HVD233, or page 13 of SN65HVD233-EP), we can see 3 clamp diodes on the output R. Can I say the upper diode which connects to VCC will provide the output R a very low impedance path to ground when unpowered? i.e. the R will keep logic '0' (dominent) when unpowered, am I right?

    Regards
    Sheng
  • 0 in reply to Sheng Wang
    TI__Guru** 103215 points
    Sheng,

    Are you saying that when the device is unpowered the Vcc rail is tied to GND or left floating? You are correct that R will stay logic low when the device is unpowered. If you would like I can measure the impedance between R/Vcc and R/GND when the device is unpowered either tomorrow or early next week.

    Regards,
    Casey
  • 0 in reply to Casey McCrea
    Prodigy 250 points
    How can I decline your great offer, Casey?

    Just a kindly reminding, when you measure the impedance of R when unpowered, it is best to measure it in two scenarias below: a) when bus line CANH='1' and CANL='0' (i.e. Dominent bit value); b) when CANH~=CANL (i.e. Recessive bit value). No rush, take your time to do this.

    Best regards
    Sheng
  • 0 in reply to Sheng Wang
    TI__Guru** 103215 points

    Hello Sheng,

    I conducted the test under two different scenarios: Vcc pin floating and Vcc pin = GND

    Vcc pin floating:

    CAN bus at dominant levels:

    Independence from R to GND = 3M Ohms

    Independence from R to Vcc pin = 3.6M Ohms

    CAN bus at recessive levels:

    Independence from R to GND = 3.7M Ohms

    Independence from R to Vcc pin = 3.6M Ohms

    Vcc pin  = GND:

    CAN bus at dominant levels:

    Independence from R to GND = 50k Ohms

    Independence from R to Vcc pin = 50k Ohms

    CAN bus at recessive levels:

    Independence from R to GND = 50k Ohms

    Independence from R to Vcc pin = 50k Ohms

    In all cases the R pin stayed at 0V dominant level. If you would like I can curve trace the pin for you and post a picture. Let me know if this helps.

    Best Regards,

    Casey McCrea

  • 0 in reply to Casey McCrea
    Prodigy 250 points
    Hi Casey,

    I have to say, I have got the most excellent tech support from you! much appreciated your help. I believe because of an engineer like you, TI's products can be sold much widerly quickly.

    No need that curve trace, and we can close the case.

    Best Regards
    Sheng
  • 0 in reply to Sheng Wang
    TI__Guru** 103215 points
    Sheng,

    Glad I could help!

    Best Regards,
    Casey