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Original question:

TIC12400-Q1: interfacing analog temperature sensors

TIC12400-Q1: TIC12400

Reshmi Garg
Prodigy 10 points
Part Number: TIC12400-Q1
Other Parts Discussed in Thread: TIC12400,

Hi Team,

The requirement for the resistor coded switch to be interfaced with the MSDI is as follows:

  • 10K when switch not pressed
  • Press to Ground when the switch is active.

and the wetting current requirement is 10mA during active state. Now when the switch is not pressed the voltage red at the INX pin would be (10mA*10K) which is 100V and this would obviously violate TIC12400 input voltage range.

Is this (simple) consideration correct, or is there any other/better way to have TIC12400-Q1 bias and read the switch values? 

  • 0
    TI__Mastermind 32970 points

    Hi Reshmi,

    The device can't create a voltage level greater than the supply voltage (VS) which is typically 12V.  The device has current source and sink circuits that will regulate and limit the current to the set levels (i.e. 10mA).  As an example, if the device was set to source 10mA out an IN pin through a switch connected directly to ground, the device would only allow 10mA of current to flow through the switch and this very low resistance.

    However, if the resistive load does not allow the full current level (i.e. 10mA) to be utilized, then the current level will be reduced accordingly.  For example, V / R = I ---> 12V / 10k = 1.2mA.

    The IN pin will not experience a 100V overvoltage condition and instead this high resistor value would limit the current as expected.

    Regards,

    Jonathan