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TS5A3359: Convert dB to resistance

Jack Loop
Guru 17870 points
Part Number: TS5A3359

I am new to this, but I wanted to ask how it would be possible to convert a dB value into resistance. I've been looking at an isolated analog switch from http://www.ti.com/lit/ds/symlink/ts5a3359.pdf that has an OFF isolation value of -64dB at 2.5v (more on pg 10), and I need help converting this. I'd appreciate any help.

  • 0
    TI__Mastermind 45340 points

    Jack,

    dB value is simply a ratio of input/output so there is not a way to convert it to a singular resistance value.

    The off isolation value on page 10 of the datasheet is an AC impedance measurement that is only valid at a specific frequency.  The measurement is taken by placing a known signal one side of the switch and measure how much of that known signal makes it to the other side of the switch when the switch is off.  The dB value is the ratio of (output/input)  You can see that there is a plot of this measurement across frequency in the datasheet while the spec on page 10 simple references this plot at a specific frequency.

    For a DC off isolation spec you can look at the off leakage current spec.  This spec is measured by placing voltages on the COM or NO pins from 0.5 V to 2.3 V and measuring the amount of current shows up on the other side of the switch with the switch off.  If you wanted to convert this in to a resistance you could use V=IR.   

    2.3V = (15nA)(R)

    R = ~153 Mohms 

    I also found this post when searching for "off state resistance"

    Thank you,

    Adam