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Original question:

TMUX136: Output level to rails?

TMUX136: very small AC signal application <10 mVpp with zero bias -5 mV to +5 mV

Vassili Ivanov40
Prodigy 210 points
Part Number: TMUX136

Hello Wittney,

I need to MUX analog sensor interface with capacitive sensor output  (<100 pF sensor capacitance)

with <10 mVpp peak signal <1mVpp typical signal and zero ground bias and current <100 uA.

In some applications the signal is typically limited by antiparallel grass clipping diodes to GND. 

Absolute rating allows signal up to -0.3 V signal. Recommended range is 0 to 3.3V. per datasheet and forum: 

e2e.ti.com/.../637888

TINA model of TMUX136 allows signal up to 500 mVpp without distortion with GND pin connected to GND and VCC to 5V.

Because schematics suggest JFET with pump voltage for the gate small negative signal should pass the switch without distortion 

and negative signal is limited by some protection diodes (ESD etc), which stays open for very small negative voltages?

Please let me know if I am right?

Best Regards, Vassili

  • 0
    TI__Mastermind 45495 points

    Vassili,

    You have a good understanding of the device but we cannot suggest you use the device outside of the recommend operating conditions.

    This device is an N channel CMOS device with its gate biased by a charge pump.  The recommended operating conditions limit the voltage on the I/O pins to 0 V.

    Thank you,

    Adam

  • 0 in reply to Adam Torma
    Prodigy 210 points

    Thank you, Adam,

    Regarding operation range, what is the accuracy for this zero in decimal points 0.1V or  0.01V? My signal is < 0.01V even peak. i.e my signal is zero and should work, if nothing special will happen just at zero voltage at drain and sink.

    The alternative with shifting ground pin to negative rail (-2V and shifting all logical levels) is worser, because of potential negative rail (GND pin) crosstalk for very small sensor signal, typically 0.1 - 1 mV.

    (unfortunately EVM does not exist for this part for a quick test with generator and oscilloscope). Sorry for bugging with details and zeros.

  • 0 in reply to Vassili Ivanov40
    TI__Mastermind 45495 points

    Vassili,

    The recommended operating range is 0 V to 3.6 V.  The abs max rating is down to -0.3 V and all abs max ratings come with this note 1.  This is the standard note for all TI device abs max ratings.

    Though possible, I do not recommend referencing the GND pin to -2 V for the same reasons you point out above. 

    The EVM can be found in the tools and software tab of the product folder on ti.com.  This is a simple passive FET switch so there are not any external components needed unless you are doing high speed signaling which will require a bypass capacitor.

    Thank you,

    Adam

  • 0 in reply to Adam Torma
    Prodigy 210 points

    Thank you very much, Adam for referencing EVM board.

    It will let me test the device under proposed conditions.

    I do not need high speed for this test.

  • 0 in reply to Vassili Ivanov40
    Prodigy 210 points

    I soldered EVM and tested TMUX136.

    It works perfectly for a small signal 10 mVpp without voltage bias or even with negative bias down to -0.2V (GND = 0V and VCC = 3.3V,  absolute maximal rating -0.3V).

    GND = 0V is a regular point for Ax / Bx / COMx. TINA SPICE model is perfectly fine near 0V = GND and down to -0.2V.