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Original question:

[FAQ] More Frequently Asked Questions about signal switches and multiplexers

TS5A3159: [FAQ] Frequently Asked Questions about signal switches and multiplexers

Ron Vogel
Prodigy 40 points
Part Number: TS5A3159


For this question, consider the following connections. 1. V+ is 5 Volts. 2. IN is at 5V. 3. COM is at GND. 4. NC is not connected.  The question is: What is the approximate switch resistance between NO and COM in the Voltage range of -0.1 and 0.0 Volts? Would the current limitations be the same in that range as it is for a Voltage in the range of 0.0 to 5 Volts?

  • 0
    TI__Mastermind 45625 points

    Ron,

    Placing a negative voltage on the signal path NO/NC/COM pins is outside the recommended operating conditions of the device.

    Placing an increasingly negative voltage on the signal path begins to forward bias the internal ESD protection diodes.  The absolute maximum ratings state that you may only pass 50 mA through these protection clamp diodes before there is risk of damage to the device. 

    Thank you,

    Adam   

  • 0 in reply to Adam Torma
    Prodigy 40 points
    Adam,
    Whether the protection diodes are PN or Metal-Semi, the current through them at 0.1 Volts would be in the microVolt or nanoVolt range. This would not exceed the current ratings, or increase the latchup danger. You high lighted note 3, which states that "The input and output voltage ratings may be exceeded if the input and output clamp-current ratings are observed." Since in my example the clamp-current ratings would not be exceeded, not even within a factor of a thousand, I assume -0.1 Volts is acceptable. My question then is, what is the I-V relation, or the resistance, at that Voltage?
    Thanks.
    Ron
  • 0 in reply to Ron Vogel
    TI__Mastermind 45625 points

    Ron,

    The on-state resistance specified in the graphs on page 10 of the datasheet from 0 to Vcc which is the recommended operating range.  The datasheet values cannot be guaranteed if the device is operating out of the recommended operating conditions.  

    Since you have IN pin biased logic high the COM pin will be conducting to the NO pin and creating a low impedance path.  Since you are operating near 0V the on-state resistance will be low about 0.8 ohms with 4.5 V supply and at 25deg V as seen in the graph above.  As the voltage on the signal path becomes increasingly negative the protection diode will begin to forward bias and create a low impedance path. 

    What you are doing with the switch that you are sensitive to -100mV?    

    Thank you,

    Adam

  • 0 in reply to Adam Torma
    Prodigy 40 points

    Adam,

    This circuit is used in ultrasonics. (I'm not sure the schematic got inserted.) The amplifier drives the transformer both positive and negative, but only when the switch is in the ground position. When the switch is in the other position, the amplifier output is zero and the echo signal from the transformer is less than 10 mV.

    Ron

  • 0 in reply to Ron Vogel
    TI__Mastermind 45625 points
    Ron,

    The schematic didn't post but the text description is also helpful.

    Keeping the voltage on the I/O pins within the absolute maximum ratings -0.5 V will not place the part at risk of permanent damage to the device.

    Let me know what additional questions you may have.

    Thank you,
    Adam