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ISO1050

Joerg Schneide
Prodigy 40 points

Other Parts Discussed in Thread: ISO1050, SN65HVD255

Hello,

I have a question re the ISO1050:

What happens when the power supply on VCC1 (logic side) is lost. Does the bus side remains recessive?

 Is the CAN bus affected in any way?

I haven't found anything on this topic in the datasheet. It is described only what happens when VCC2 is lost .

Thank you,

Joerg 

  • 0
    Prodigy 40 points

    I could not wait any longer for an answer and made a short test.

    May be  the result is of interest for others too.

    With open RXD an TXD pins I have seen nothing malicious on the CAN-Bus while switching VCC1 on and off and in permanent off.

    With pin TXD tied to GND1 there is a short  period with a dominant state after switching VCC1 on until the Dominant Timeout kicks in.

     The test was made with the ISO1050DUB, I hope the ISO1050DW behaves the same way.

    Joerg. 

  • 0 in reply to Joerg Schneide
    TI__Mastermind 20600 points

    What you see on the bench is correct. The ISO1050, both DW and DUB, have TXD Dominant time out.  If VCC1 is lost or the TXD on the logic side would get stuck dominant (logic high) for any reason the TXD DTO on the transceiver, which is the last step prior to the CAN bus (driver outputs) will ensure the bus is protected and placed into recessive state ater the TXD DTO time of the CAN transceiver in the ISO1050.  As with any system fail corresponding the the TXD pin of a powered CAN XCVR their may be some dominant output which could corrupt the bus data for a short period of time prior to the TXD DTO kicking in and protecting the bus.  If you want more detailed information on CAN TXD DTO there is a section on page 5 in the SN65HVD255 datasheet explaining this in detail including the method to calculate the impact on minimum data rate due to the TXD DTO in the CAN system, the application is the same, however the TXD DTO of the 255 is much longer (allows lower data rates) than in a 1050 / ISO1050 CAN transceiver.  This HVD255 datasheet may be found at:  http://www.ti.com/lit/ds/symlink/sn65hvd255.pdf

    -- Scott