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Need Buffer OP AMP Design to drive long high capacitance cables

Govind K
Intellectual 510 points
Other Parts Discussed in Thread: F28M35H52C, TIPD128, OPA316, OPA4172

Hello,

I need to interface an analog hall effect sensor to ADC ( F28M35H52C controller) which is 10 meter away. Design Specs are given below.

Sensor: SS39ET/SS49E/SS59ET Series Hall effect sensor. 

Output: Sine wave whose magnitude varies from 1V to 4V (1V DC offset), 300Hz Maximum frequency. Supply Voltage: 5V

Controller: F28M35H52C, ADC reference supply: 0 to 3.3V

As per my understanding, one options is to use Op Amp buffers which can drive high capacitance cables ( Consider 1uF ). 

Kindly suggest the OP-Amps / Designs for my application. Also suggest better alternative if required.

Thanks in advance,

Regards,

Govind.

  • 0
    TI__Intellectual 1190 points
    Hello Govind,
    We are currently sampling an Opamp that can do this. Are you connected with any TI sales/FAE?
    Thanks,Andrew
  • 0 in reply to Andrew Leverette
    Intellectual 510 points
    Hello Andrew,
    Yes, i know couple of TI sales guys who are located in Bangalore, India. Can you tell me the part number of the OP-Amp?? I Will check for the samples availability. Meanwhile, i request your opinion on implementation of this circuit.
    - Do you expect any instability issues with Op-Amp when driving long cables??

    Thanks & Regards,
    Govind.
  • 0 in reply to Govind K
    TI__Intellectual 1190 points
    Hello Govind,
    Our opamp is designed to be stable with very big capacitive loads. 1uF may be pushing it. However, you can use series resistance to stabilize. Please contact the sale person that you know and have them contact me. I believe we can share some more collateral and information for effectively through that channel.
    Thanks,Andrew
  • 0
    TI__Guru**** 154026 points
    Govind,

    For output, please add more detail. Is 1V to 4V magnitude magnitude in Vpp? Is 1V offset relative to average or minimum output voltage?

    What type of cable is going to be used?
  • 0 in reply to Ron Michallick
    Intellectual 510 points

    Hello Mr. Ron,

    The Minimum sensor output voltage is 1V,  then increases to 4V ( When magnet approaches the sensor) in sinusoidal manner. 

    And then, deceases to 1V from 4V (When magnet going away form the sensor) in sinusoidal manner. A screen shot of transfer function from sensor datasheet is attached here for more understanding. 

    Sensor Part number: SS39ET/SS49E/SS59ET Series, Make: Honeywell.

    Even though the transfer characteristics shows it as straight line, please consider output as sine wave (actual wave form depends on shape of the magnet.) Output frequency varies between 0Hz to 300Hz depending on the speed of the object.

    Kindly let me know if miss anything. Thanks in advance.

    Regards,

    Govind. 

  • 0 in reply to Govind K
    Intellectual 510 points
    Hello Mr. Ron,
    Sorry, I forgot to mention cable details. Exact cable part number is not identified yet (customer not finalized).
    I can give basic info:
    Round cable, Twisted pair 22 AWG to 24 AWG, Length 10 meters, Please assumes capacitance as nearly 1uF. we will try to use low capacitance cables to keep total capacitance bellow 1uF for 10 meter length.

    Regards,
    Govind.
  • 0 in reply to Govind K
    TI__Guru**** 154026 points
    Govind,

    I can get some 1uF load wave forms in Early January.
  • 0 in reply to Govind K
    TI__Mastermind 25815 points
    Hello Govind,
    There is a TI Precision Design that may be of help here. Please take a look at TIPD128.
  • 0 in reply to Pete%20Semig
    TI__Expert 6275 points

    3443.OPA316 Cap Drive.pptx

    PowerPoint file details a way for you to drive your cable capacitance with just about any op amp for this application with accurate output at the transmit end of your cable.

  • 0 in reply to Tim Green1
    Intellectual 510 points

    Hello Mr. Tim Green,

    1. OPA316 Op-Amp suggested by you is not available in SOIC-14 package. We are specifically looking for same package to maintain comparability with our previous designs.
    As per your inputs i selected which are in SOIC - 14 package :
    1) OPA4234
    2) OPA4172
    Can you please suggest if i can get same response as OPA316 with 100nF load ..? (Reduced the cable length & using low capacitance cable)


    2. OPA4172 has output current capacity of +/-75mA @ 36V supply voltage. Can you please let us know if the output current is same for 5V supply voltage.?

    Thanks & Regards,
    Govind.