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TS5A3359: Reducing 4-minute-long settling time

Brad Nelson99
Intellectual 325 points

Part Number: TS5A3359

I am currently testing a design in which a 3-way switch is used in conjunction with a wheatstone bridge to switch between multiple sensors and resistors, as shown below.

When the device is tested, the resistance of the switch changes by about 1.5 ohm (from 3.3 ohm to 4.8) and slowly settles back to its original value after about 4 minutes. The amplified voltage is shown below. at t<0, the switch is set to resistor R1 to show the baseline, then quickly switched to R2 (resulting in a spike) and back to R1.

Is this sort of settling time expected? Is it possible to reduce the settling time of this switch?

  • 0
    TI__Mastermind 45730 points

    Brad,

    The TS5A3359 like all signal switches on-state resistance (Ron) will vary on supply voltage (gate of the FET), input/output voltage (Drain/Source of the FET), and temperature.  

    The TS5A3359 is a passive FET switch and doesn't have any source or sink capability.  This means the settling time of the bus with NO and COM pins will be determined by the source and load.  The TS5A3359 will have some parasitic capacitance (78pF) you will also want to include in your calculation of the RC time constant. 

    You may also want to be aware of charge injection which can cause a momentary error in voltage measurement when changing switch states. 

    What is your application?  What type of sensors are you using?

    Let me know if you have additional questions.

    Thank you,

    Adam

     

  • 0 in reply to Adam Torma
    Intellectual 325 points

    The application is for a strain gauge, and the sensor is a resistive strain gauge. The switch is in place to reroute the leg of the bridge to some known resistors to provide a known baseline when the sensors are inaccessible. The switch is controlled by a microcontroller.

    As far as capacitance goes, the load should have pretty low capacitance, but the source provided to the COM is regulated to a constant voltage so that has a fairly high capacitance. Is there a good way to improve this other than decreasing the capacitance on the regulator?

  • 0 in reply to Brad Nelson99
    TI__Mastermind 45730 points
    Brad,

    As far as the switch is concerned you cannot do much to reduce the settling time because it is dependent on the other components in your system. Are you able to reduce the RC time constant by choosing a smaller reference resistor?

    Adam
  • 0 in reply to Adam Torma
    Intellectual 325 points

    I'll look into it. Thank you for your help.