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TLV4170: TLV4170

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Replies: 8

Views: 938

Part Number: TLV4170

Dear sir,

We are started developing product based on TLV4170. We are designing analog card which is measure voltage 0-10V & 4-20mA.We attached both schematic with this thread.

                             0-10V  input

           4-20mA input

We facing problem in 2 issues in both circuit.

First is, if not connect anything to input means input is open then some minor voltage generate at output of the OP-Amp.

Second is, We used ST microcontroller which as inbuilt 12bit ADC. When we start sampling of OP-Amp output then it's showing triangular wave in Oscilloscope & if we not sampling the OP-Amp output then showing constant voltage. In this issue if we used LM358 OP-Amp then this issue is not happen.

We have very less knowledge about Analog design.

Thank you 

  • Hi Ravikant,

    Can you try attaching the schematics again? I can't see any images. If you use the link "Insert Code, Attach Files and More" you'll be able to access a rich text editor and you can attach the images.

    For your first question, all op-amps have what is called an input offset voltage. I recommend you watch the first video of TI Precision Labs which covers this topic: training.ti.com/ti-precision-labs-op-amps-vos-and-ib

    I'll be able to more easily address your second question with a schematic. My guess is that there is a capacitive load which is being charged when you're sampling.

    Thanks!
    Paul
  • In reply to Paul Goedeke:

    Dear Sir,

    Thanks for your valuable replay. Please check image which attached  below.

                                                                        Voltage Input

                                                    Current Input

  • In reply to Ravikant Dalsaniya:

    Thanks for the additional information. The schematics are helpful but didn't answer as many questions as I had hoped.

    Which signal, VOUT1 or AOUT1 go into the ADC? My guess would be that VOUT1 is what is driving the ADC, but please confirm. For the first circuit, it will be important to check the stability of that circuit as well as make sure you have the right output RC values for the ADC's sampling frequency. I recommend using the Analog Engineer's Calculator (www.ti.com/.../analog-engineer-calc) which has a section that will help you calculate the right values.

    I looked at the stability of the voltage input circuit and it looks good to me. Your value R51 may be too high which would slow your response time down. The phase margin is about 80° and you probably don't need that much. Take a look at TI-Precision labs and the videos on Op-amp stability: training.ti.com/ti-precision-labs-op-amps-stability-5

    Can you provide information on the input signal VIN1+?
    Scope-shots of the input and output waveforms with and without the ADC connected would be helpful as well.

    You may want to consider using an XTR and look at TIPD190 and TIPD195. This forum post may be of use too:
    e2e.ti.com/.../431250

    Thanks,
    Paul
  • In reply to Paul Goedeke:

    Sorry for missing information,

    VOUT1 & AOUT1 connected to ADC. Your guessing is correct.

    VIN1+ -> 0-10V input
    AIN1+ -> 0-22mA input

    Thanks again.
  • In reply to Ravikant Dalsaniya:

    Thank you. Both VOUT1 and AOUT1 are connected to the ADC? I assume on different channels? Which has the triangular effect?

    Is the input VOUT1 a DC value or AC value?

    Please provide scope-shots of the input and output waveforms with and without the ADC connected.

    -Paul
  • In reply to Paul Goedeke:

    VOUT1 is DC value.

    Yes, Both are connected to different channels.

    Scope-shots provide will be very soon.

    Thank you.
  • In reply to Ravikant Dalsaniya:

    Hi Ravikant,

    Do you have any further inputs or questions? Otherwise I will close this thread.

    Thanks,
    Paul
  • In reply to Paul Goedeke:

    Dear sir,

    Issue fixed. Close this thread.

    Thanks again,

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