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TMUX1309: Ron value

Isaac Wang
Prodigy 10 points
Part Number: TMUX1309
Other Parts Discussed in Thread: TMUX1208

The TMUX1309 datasheets shows that Ron under the 25C and 1.8V operations condition can reach 1500ohm MAX, yet the bandwidth section shows that this part can support up to 350MHz. It's not clear to me how a Ron (series R, if I am not mistaken) of this high would make it useful in any application, not to mention the 350MHz bandwidth. Did I miss something?

  • 0
    TI__Mastermind 28978 points

    Hey Isaac,

    The higher Ron at 1.8V isn't always going to be an issue. In low impedance applications, you do have a point that this device shouldn't be used because of the high resistance and your drop may be too large but in digital applications where the load is much greater than the On-resistance (you can correct that this is the series R), this wouldn't be an issue. This is where the 1308 is typically used, where you find a digital input or a high impedance load for an analog application.
    The resistance isn't the only thing that effects bandwidth. On capacitance, which is 11pF at the given conditions and the load will affect the bandwidth more than just the on resistance. The load that it is tested with is given in the datasheet. The bandwidth is restricted by the effective thevenized RC circuit (really just a low pass filter) created by the Ron Con RL and CL. You can use the equation found in this video ( Precision Labs - Switches and Muxes: bandwidth, crosstalk, off-isolation and THD+Noise) to approximate the 3 db cutoff too. This is really just a rough approximation though and I wouldn't rely on it as absolute, seeing as how our muxes typically will perform better than what the equation reflects. That being said, the device is tested and the bandwidth is derived from actual testing measurements not from mathematical estimations.

    If you're concerned about the Ron value, the TMUX1208 will have a lower Ron. Note though that the bandwidth is lower since the on capacitance is greater, which will have more impact on the BW.

    Thanks,
    Rami