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TCAN1042HG: TCAN1042 current limit resistor on RXD

Yang Wu
Expert 3370 points
Part Number: TCAN1042HG


Hi Team,

I see in the datasheet of TCAN1042, it says IOH/IOL(RXD) = 2mA, and in order to limit current of digital lines, serial resistors may be used (R2 & R3 shown below).

my question is how to calculate this current limit resistor value to make sure driving current is within 2mA, if I connect RXD & TXD to TMS320F28374D directly, is there any risk to damage? 

Thanks  a lot.

\

Best regards,

Yang

  • 0
    TI__Guru 53575 points

    Hi Yang,

    Most microcontroller input pins will only have very small leakage paths (~2uA for the one listed) and will not come close to overloading the digital output pins of TCAN1044. This will be more of a consideration for sizing external pull-up resistors if such a bias is desired. The series resistors on these digital lines are more often used to limit the switching current through the signal lines during transitions to limit EMI. Typical values for such resistors will be between 10-ohm and 33-ohm. In order to most effectively reduce this EMI, the limiting resistors should be placed near the signal driver. So R2 would be placed near the MCU and R3 placed near the transceiver. 

    Let me know if you have any more questions.

    Regards,
    Eric Schott