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TMP411-Q1: question about "series resistance cancellation "

Jay wang
Intellectual 1831 points
Part Number: TMP411-Q1
Other Parts Discussed in Thread: TMP411

Hi Sensor Team,

I have some questions about  "series resistance cancellation" as shown in TMP411 datasheet. Basic Connections of TMP411 is shown below. 

Q1: How to understand "series resistance"?

(it means Rs as showing in Basic Connections of TMP411 or  only PCB trance resistance and remote line length  or RS+PCB trance resistance and remote line length  )

Q2:How to place Rs as showing in Basic Connections of TMP411?

(near Transistor or near D+D-)

Q3:How to make sure the Rs specific value in the application?

Q4:How tmp411 do the cancellation inside?  I cannot find detailed interior block diagram in datasheet.

Q5:Why is 3kohm series resistance the max limitation?

  • +1
    TI__Mastermind 37835 points

    Hi Jay,

    1. The feature 'Series Resistance Cancellation' eliminates measurement errors caused by the Rs shown in the diagram. 

    2. It's common practice to place the Rs and Cdiff near TMP411.

    3. Rs is not required for operation. In some cases, Rs and Cdiff can minimize noise found in the end equipment. The resistance is specified as 3kOhm max, but TMP411 will not eliminate all error up to 3kOhm, see Figure 4 and 5. Note that series resistance is the total loop resistance including the sum of both Rs resistors.

    4. The implementation of Series Resistance Cancellation is proprietary, confidential. 

    5. The remote junction is excited using a current source, and the voltage is measured by the sensor. The excitation currents, cycle timing and voltage operating range are all constants in the design. The voltage developed across the junction must settle within the cycle time to properly acquire the signal with the internal ADC. Excessive resistance will also push the voltage beyond the ADC's operating range. 

    thanks,

    ren

  • 0 in reply to Ren Schackmann
    TI__Intellectual 1831 points

    Hi,Ren

    Thank you for your timely response.   

  • 0 in reply to Ren Schackmann
    TI__Intellectual 1831 points

    Hi Ren

    I have a question about Q3.How to calculates a specific value. Is there a formula or way?

  • +1 in reply to Jay wang
    TI__Mastermind 37835 points

    Jay, I'm not sure I understand your question, but there aren't any formulas associated with question 3.

    thanks,

    ren