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ISO1042-Q1: slew rate spec of CAN H/L Differential output.

Part Number: ISO1042-Q1
Other Parts Discussed in Thread: ISO1042

Dear Sir,

Could you let me know slew rate spec of CAN H/L Differential  output.

My customer spec is as below.

slew rate : Spec 20 ~ 40 V/us

Thanks.

  • Hi Dexter,

    I do not think we characterize device specifically for differential output slew because this largely depends on the overall load capacitance on the CAN transceiver including bus capacitance. But using the differential output rise time spec and differential output voltage spec from ISO1042 datasheet, I could estimate the slew rate to be as below,

    Test condition: VOD(DOM) = ~1.5V to 3V, tR = 45ns (typical) for RL = 60Ω, CL = 100pF assuming input signal rise time at TXD = 1ns
    Slew rate = 33 - 67V/µs

    Please note that this is typical data for given test conditions, the range can be wider or different based on the test conditions. Thanks.

    Regards,
    Koteshwar Rao

  • Hi Koteshwar Rao,

    Could you calculate estimate slew rate for below condition.

    otherwise can you share calculate tool?

    RL= 60Ω, CL = 50pF.

    Thanks for your support.

  • Hi Dexter,

    Unfortunately, we don't have differential output rise/fall time characterized for CL = 50pF and hence I cannot provide you the actual slew rate data that can be observed from device.

    I can still use the 100pF test data and theoretically calculate slew rate for 50pF capacitive load making some assumptions.

    Calculation for CL = 100pF:
    Test condition: VOD(DOM) = ~1.5V to 3V, tR = 45ns (typical) for RL = 60Ω, CL = 100pF assuming input signal rise time at TXD = 1ns
    Slew rate = VOD(DOM) / tR = (1.5V to 3V) / 45ns = 33 - 67V/µs

    Calculation for CL = 50pF:
    tR (10% to 90% point, CL@100pF) = ~2*R*CL = 45ns
    Therefore, R = 45ns / (2*CL) = 225Ω
    tR (10% to 90% point, CL@50pF) = ~2*R*CL = 22.5ns
    Slew rate = VOD(DOM) / tR = (1.5V to 3V) / 22.5ns = 67 - 133V/µs

    Regards,
    Koteshwar Rao