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EVM430-FR6047: USS CH0/CH1 resistor & capacitor values

Foz Hughes
Prodigy 125 points

Part Number: EVM430-FR6047

Hello,

In the USS subsystem of the EVM430-FR6047, the CH0/1 OUT/IN pins are routed through a series resistor and capacitor (R16 and C11 for CH0, R17 and C12 for CH1).  Can you explain how the values of these components were chosen?

We are attempting to optimise our system by adding an impedance matching network and would like to understand whether changing the values of these components would have any benefit.

Many thanks.

Foz

  • 0
    TI__Expert 7515 points

    Hi Foz,

    The values of the resistors R16, R17 are chosen based on the approximate impedance of the transducers at 1 MHz used in water flow meters.

    Please look at section 21.3.2 Trim Registers for the Output Drivers and Termination Resistors of the Device Family's User's Guide (https://www.ti.com/lit/pdf/slau367). The on-chip trim of the resistors takes care of the required matching of the impedance of the two channels.

    I think you can definitely get improved performance with well-matched transducers whose natural resonant frequency does not vary much over variation of temperature of water. We are not sure how much more improvement you can get by additional matching.

    Srinivas

  • 0 in reply to Srinivas Lingam
    Prodigy 125 points

    Hi Srinivas,

    Thank you for your response.

    We have found that we can increase the amplitude of the received signal by as much as 20% with the addition of a small inductance in parallel with the transducers.  We think this may be because the resonant frequency of our transducers does not precisely match the 1MHz drive signal.  We were hoping to be able to tune the resistors R16 and R17 to take this into account, hence the original question.

    How could we calculate the most appropriate value for these resistors based on the resonant frequency of our transducers?  I am happy to send you a full impedance scan of a transducer if that helps.

    Many thanks,

    Foz

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