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TIC12400-Q1: About VCSI_DROP_OPEN/CLOSED

Lee, Sam
Expert 4935 points
Part Number: TIC12400-Q1

Hi team,

Could you pleae give more description about VCSI_DROP_OPEN and CLOSED spec specified in TIC12400-Q1 datasheet? 

I refer to below blog but ask somoe questions.

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(https://e2e.ti.com/support/interface/f/138/p/837008/3100285?tisearch=e2e-sitesearch&keymatch=TIC12400%20VCSI_DROP_OPEN#3100285)

"VCSI_DROP_OPEN is maximum voltage drop across the current sink in a switch open (RSW(MIN) = 5kohm) scenario. The comparator threshold settings (2V, 2.7V, 3V, and 4V) are all above 1.7V so there shouldn’t be any issue distinguishing an open (INx voltage between 0 and 1.7V) vs. closed (INx voltage is pulled up close to the battery level) switch.

VCSI_DROP_CLOSED is a spec for the Matrix mode operation (Refer to the datasheet). In Matrix mode, both the current sink and current source are turned on together, and there will be certain voltage drop across the current sink depending on the setting used. This spec is not relevant to your particular use case."

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-. In switch open, dees the RSW mean the inernal resistance inside decie or the exteranl switch's resistance?

-. When calulating external resister on the CSI settings, should the INx be considered including the max 1.7V as (VS - IR drop - max 1.7V)?

-. As for VCSI_DROP_CLOSED, if the use case is not matrix mode, does the voltage drop need not to be considerd for any calculation of external resistors? And what is the IIN?

Thanks,

Sam Lee

 

  • 0
    TI__Expert 3800 points

    Hi Sam,

    Thank you for posting these questions. 

    • Rsw is the external switch's resistance, see Figure 17 for reference.
    • Can you share a bit more detail what exactly will be done? If you are using Resistor-coded Switches Detection please follow the instructions in chapter 9.3.2
    • IIN is the current flowing into the INx pin. As the voltage is measured after the internal switch you'll have to consider it in you calculation.

    Best regards,

    Ambroise

  • 0 in reply to Ambroise Suter
    TI__Expert 4935 points

    Hi Ambroise,

    Thank you for your reply.

    -. I'd like to double confirm it about that. The max. 1.7V of VCSI_DROP_OPEN is caused by internal resistance at current sink, regardless of the exteral resistance. Is it correct?

    -. In addition, belwo is an example of Grounded connected switch. Is the calucation right? Which threshodl should I use? min or max?

     

    Thanks,

    Sam Lee

  • 0 in reply to Lee, Sam
    TI__Expert 3800 points

    Hi Sam, 

    as the external Resistors will impact the current flowing into INx the voltage drop will change due to the internal components (resistors, switches, etc.). The exact voltage drop is best measured on the TIC12400EVM. 

    Can you add more details which instruction you are using to create the attached matrix? And can you add the units to all rows?

    Best regards,

    Ambroise

  • 0 in reply to Ambroise Suter
    TI__Expert 4935 points

    Hi Amboise,

    Sorry. I added the units in the table. I used the equation of INx = total registance(R1+Switch R) x wetting current + GND shift margin. Is it okay? Also, to select the comparator threshold, what value should I use, min or max?

    Thanks,

    Sam Lee

  • 0 in reply to Lee, Sam
    TI__Expert 3800 points

    Hi Sam,

    your calculations look good, for the threshold voltage you have to check with chapter 5.2 in out configure guide. The selection of Vth also depends on Vsource (VS).

    Let us know if you need further help.

    Best regards,

    Ambroise