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Original question:

TIC12400: design confirm

TIC12400-Q1: IN18~IN23 two switch detect

jincheng peng
Prodigy 21 points
Part Number: TIC12400-Q1
Other Parts Discussed in Thread: TIC12400,

hello, experts

The In18 to In23 of the TIC12400 can detect 2 switches.Are there some special requirement for the switchs?

Can you tell me Which controller manufacturers have used a scheme to detect 2 switches?

  • 0
    TI__Mastermind 33370 points

    Hello Jincheng,

    The TIC12400-Q1 has to options for monitoring switches for a state change.

    The first is a comparator which is usually used with a single switch per input channel and can detect a voltage above or below a threshold such as a short to ground or to the supply voltage. This is effectively a digital switch with the switch either being Open or Closed.

    The second option is to use the internal ADC to measure the actual voltage on the input pin and can be used as an analog switch.  You can configure the thresholds with specific ADC values to allow detection of whether a switch is open or closed based on the voltage levels.  Multiple switches can be connected to the same input put if they have different resistance values such as a multi-position switch and are commonly referred to as Resistor Coded Switches.  Because each switch position will cause the wetting current to flow through a different resistor value, the corresponding voltage measured by the ADC will be different for each switch and therefore you can determine which position the multi-switch is in.

    I'm not sure why you have singled out inputs IN18 to IN23 because all input channels of the TIC12400-Q1 can be used with the ADC.  The only requirement for detecting multiple switches on a single input pin is that they have different resistance values and that the ADC is used as the detection method.

    For your second question, I support the TIC12400-Q1 from a device level, but I am not able to provide any information on how any of our other customers may have used this device in their designs.

    Regards,

    Jonathan

  • 0
    Prodigy 21 points

       I want to know when to sample the INx.

       pls see the 30th page of the TIC12400 DS. "At the end of the wetting current application, the input voltage is sampled by the comparator (if input is configured as comparator input mode) or the ADC (if input is configured as ADC input mode)"

       pls see the figure 26 of the 31th page of the TIC12400 DS again. it seem mean "At the start of the wetting current application, the input voltage is sampled"

       I am confused about when the INx is sampled

  • 0 in reply to jincheng peng
    TI__Mastermind 33370 points

    Hello Jincheng,

    Wetting current is applied to the INx channel for a specific amount of time that can be configured between 64uS and 2048uS.  This is set by the POLL_ACT_TIME field (bits 8:5) in the CONFIG register (0x1A).  This allows the voltage to charge any capacitance and stabilize before the INx channel is sampled at the END of this time. 

    There are two types of modes in the device that controls how the wetting current is applied.  In Continuous Mode, the wetting current is always applied to the INx channel and is not turned off after the channel has been sampled.  In Polling Mode, the wetting current is turned off after the INx channel has been sampled.  It remains off while the other channels in the cycle are being sampled and it is turned back on when it is time to sample the INx channel again.

    Regards,

    Jonathan