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PGA460-Q1: Damping resistor selection for avoid electric charge accumulation

PYTsai
Genius 11645 points
Part Number: PGA460-Q1
Other Parts Discussed in Thread: PGA460

Hi 

in our application we have two configuration

Our 1st configuration is Direct drive mode, the pulse amplitude is 7V and pulse frequency is 200KHz. 

   The application note PGA460 Ultrasonic Module Hardware and Software Optimization suggest 500 Ω to 25 kΩ, damping resistor. 

   We saw some of the transducer datasheet suggest adding a 100K ohm parallel resistor to prevent the electric charge from accumulation. For such transducer how do we select our damping resistor.  

Our 2nd configuration : Transformer mode, the pulse amplitude is 90V . 

   Same question, We saw some of the transducer datasheet suggest adding a 100K ohm parallel resistor to prevent the electric charge from accumulation. For such transducer how do we select our damping resistor.  

  • 0
    TI__Mastermind 27950 points

    PYTsai,

    A damping resistor is typically used to help critically decay the transducer ring-down time to improve short range performance. A value of 100kOhm is very high compared to the recommend range. Most transducers seem to pair well with a 10kOhm damping resistor.

    To help you determine what damping resistor is sufficient for your application, place a target at your maximum expected distance, and spot check or sweep the damping resistor value by using a potentiometer in parallel to the transducer. As you are changing the values, observe the peak amplitude from the target's echo response. You will want to choose a value that yields an SNR of at least 2:1, but preferably 3:1.

    Depending on your short range requirement, you may not even need to use a damping resistor, and using a 100kOhm bleed resistor in parallel to the transducer in both the direct-drive and transformer-drive modes is a good idea.