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SN65MLVD206B: Is SN65MLVD206B a constant current output device?

Yunjing Wang1
Expert 3190 points
Part Number: SN65MLVD206B

Hi team,

My customer is evaluating SN65MLVD206B as backplane bus, they are finding a best choice for 150Mbps, so they tried many termination values.

However, when they use 43R as the two termination resistors value,(means 43R//43R = 21.5R equivalent differential impedance ), the V_AB is still 430mV, not 11.3mA*21.5 = 242.9mV.

Is SN65MLVD206B is a 11.3mA constant current output device as TIA/EIA-899 limit?

If yes, can you help comments why two 43R termination resistors in parallels leads to 21.5R equivalent impedance, but get 430mV not 11.3mA*21.5 = 242.9mV?  

Thank you!

Best regards

Yunjing

  • 0
    TI__Mastermind 35130 points

    Hi Yunjing,

    The TIA/EIA-899 standard specifies that drivers should provide greater than 300mV to loads between 30-ohm and 55-ohm. 21.5-ohm is outside of the operating region and so will not have a linear relationship. However, since they're still measuring 430mV that means the SN65MLVD206B has enough current drive to drive a 21.5-ohm load and keep the differential voltage within datasheet specifications. 

    Also, please note the termination resistors must match the characteristic impedance of their transmission line.

    Regards,

    I.K. 

  • 0 in reply to Ikechukwu Anyiam
    TI__Expert 3190 points

    Hi I.K.

    Thanks for your reply, some further questions:

    Q1: Based on your feedback, SN65MLVD206B is a current output device, but can only guarantee a linear relationship between 30-ohm~55-ohm load and device output current, as TIA/EIA-899 standard specifies. Correct ?

    Q2: what is the output current value when load is between 30-ohm and 55-ohm? 11.3mA?

    Q3: When load is smaller than 30-ohm, what is the output current value turns to be? 

    Q4: Seems 430mV/21.5=20mA less than SN65MLVD206B short circuit current 24mA and will not cause short circuit damage, but is there any potential risk for SN65MLVD206B device to drive like 21.5R load? 

    Thanks and best regards

    Yunjing

  • 0 in reply to Yunjing Wang1
    TI__Mastermind 35130 points

    Hi Yunjing,

    1. Correct

    2. Going by datasheet specifications it looks to be 13 - 16mA

    3. The device has not been characterized for loads under 30 ohms

    4. There's no risk to damage the device by driving smaller loads. But again, the termination resistance needs to match the characteristic impedance of the transmission line.

    Regards,

    I.K.