• TI thinks resolved

SN74CBTLV3126: Does it support SMI (MDC/MDIO)

Part Number: SN74CBTLV3126

Hi team, 

    Does SN74CBTLV3126PWR support SMI interface? 


  • Alan,

    To determine if a switch can support a specific signal standard you are correct to look at the datarate and voltage level of the standard. 

    Do you know what data rate and voltage Serial Management Interface (SMI) you are trying to support?  What I have seen is that it can be up to 2.5MHz  

    The SN74CBTLVXXXX family of devices will support 200MHz bandwidth or up to 300Mbps data rate. 

    The propogation delay spec you mention above should not be an issue since almost all passive FET switches propogation delay is <1ns. 

    Let me know if this helped.

    Thank you,



  • In reply to Adam Torma:

    Hi Adam,

       I get customer feedback about voltage level as below:

    VIH = 2.1945V - 3.535V
    VIL = -0.4V - 0.9405V

       Can you please confirm these spec. within our spec.?


  • In reply to Alan Chang:


    Based on the same appnote referenced above you can see that the SN74CBTLVXXXX family of switches are bilateral switches that have an n-fet in parallel with p-fet.  This means that the device can support signals from 0 to Vcc.  The graph below shows that placing a voltage on the input (Vi) results in the same voltage on the output (Vo).

    If you're requirements above state you need to pass a signal as high as 3.5 V you will need to set Vcc of the SN74CBTLVXXXX device > than 3.5 V. 

    On the low side of your signal range passing a signal -0.4 V is not recommended.  It is within the absolute maximum ratings in the datasheet but may cause some extra leakage current through the switch due to the ESD protection diodes.  Since you are using this switch for a digital signal the extra leakage should not impact your signal but make sure that your other devices in the signal chain will not be damaged by the negative voltage.

    Thank you,