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INA148 + single-ended amp with digital control

Vladimir Naumenkov
Expert 2970 points

Part Number: INA148
Other Parts Discussed in Thread: PGA281

Dear Marek, thank you

I, probably,  will use INA148 for receiving signal from a  two-wire line. I have a long two-wire line - more than 10 km. 

Please, report

1) What max DIFFERENTIAL  input voltage can withstand  INA148 ? Power supply is +/- 15 V. 

I mean the maximum value of the voltage at which it will not fail.

2) I'd like to use circuit figure 5, page 10 of INA148 datasheet.  How do you think, can I use it for receiving signal 50 - 1000 Hz, +/- 50 mV  to  +/- 12 V ?

3) Can you recommend  amplifier  with single-ended input and with digital control? Power supply +/- 15 V. Input signal frequency 50 - 1000 Hz,  +/- 12 V .  It is desirable that the minimum gain is 0.05 or close to that.  I need  single-ended amp with digital control to set after INA148.  

TIA

Sincerely

Vladimir Naumenkov

www.agat.by

  • 0
    Guru 140200 points

    Hi Vladimir,

    I'm not Marek, but perhaps I might be allowed to say a brief word?

    A 10km long cable can transport huge common mode overvoltages during a thunderstorm. So, you will need a real proper lightning and surge protection at the input of your circuitry.

    Then, I would use a transimision method which can handle much higher common mode voltages like a transformer or, better, optical isolator.

    Kai

  • 0 in reply to kai klaas69
    Expert 2970 points

    Dear Kai, thank you

    We use lightning and surge protection at the input of our circuitry.

    But as for the transformer or something else ..... yes, it's worth considering. Actually, in our previous device, the diff amplifier input was connected directly to the line. I can’t say that everything worked without accidents during a thunderstorm... But the price also plays a significant role. We have a lot of these communication lines - several  thousand, and then a transformer must be installed in each line ... These are the lines that connect the traffic light controllers to the control center.  

    And if to use an isolated amplifier, then it must be powered from both sides - this is also inconvenient, but such amplifiers are expensive.

  • 0 in reply to Vladimir Naumenkov
    Guru 140200 points

    Hi Vladimir,

    an optocoupler doesn't need supply voltages on both sides.

    Kai

  • 0 in reply to kai klaas69
    Expert 2970 points

    Dear Kai, thank you

    Our device is the transmitter/ receiver. 

    We use optocoupler  for transmitting signal in the line. But  it is not good  for receiving signal, because the received signal may be attenuated at the input of the our device to a value of 100 mV or less. 

    Vladimir Naumenkov

    www.agat.by

  • 0
    TI__Guru 73981 points

    A good exchange of ideas, guys.  Please see below the answers to your other questions:

    1) What max DIFFERENTIAL  input voltage can withstand  INA148 ? Power supply is +/- 15 V. 

    I mean the maximum value of the voltage at which it will not fail. 

    Since the differential impedance of INA148 is 2Mohm and the ESD diodes may carry up to 10mA current, it would take +/-10kV to damage the part.

    2) I'd like to use circuit figure 5, page 10 of INA148 datasheet.  How do you think, can I use it for receiving signal 50-1000 Hz, +/- 50 mV  to +/-12V?

    Yes, it there should be no issue with measuring your input signal.  Since the output swing is limited to 1V below a positve rail, using Vref=0 would allow you to measure differetial signals up to +/-14V (see below).

    3) Can you recommend  amplifier  with single-ended input and with digital control? Power supply +/- 15 V. Input signal frequency 50 - 1000 Hz,  +/- 12 V .  It is desirable that the minimum gain is 0.05 or close to that.  I need  single-ended amp with digital control to set after INA148.  

    Look into using PGA281