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ISO7740: TI isolation advantage with Cio 1pF

Masaharu Takahashi
Expert 4170 points
Part Number: ISO7740

hi, Team

could you tell me below?

1.How we make it such a small cap as 1pF?

2.why does small cap value bring good thing?

  • 0
    TI__Genius 17100 points

    Hi Takahasi-san,

    Thank you for your post! The Cio value is an effective capacitance between ISO77xx input and output pins. This capacitance is not exactly the value of the series isolation capacitors, but the isolation capacitors are constructed using TI's silicon process with several layers as shown on TI.com/isolation.


    Respectfully,
    Manuel Chavez

  • 0 in reply to Manuel Chavez
    TI__Expert 4170 points

    is there any meaning for that value?

    should customer like "big value of Ciso" or "Low" and Why ?

  • 0 in reply to Masaharu Takahashi
    TI__Genius 17100 points

    Hi Takahashi-san,

    This capacitance is a representation of all the capacitances that exist in the device between input and output pins, including the isolation capacitance and parasitics.

    Small Cio values are better because any parasitic capacitance tends to become a coupling path for common mode transients, which reduces CMTI and can corrupt data in the presence of transients, so this is also an advantage against optocouplers  which typically have poor CMTI due to their large Cio capacitances. CMTI is an important concern for many applications including Motor Drives, Power Delivery, Solar Inverters, and Medical.


    Have a great weekend!

    Manuel Chavez