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OPA602: OPA602 parts related technical inquiry

Part Number: OPA602

Dear TI,

Technical inquiry about the following products.

1) Problem description
 - The value of 15mA output was set by using current amplifier OPAMP (OPA602) using REF200AU product.
15.3mA was measured at the time of single operation, but it was confirmed to be 10.5mA at the time of functional operation measurement.

2) Connection configuration
 - REF200AU 2ch 100uA bundled together
 - OPA602 (1EA), 200uA is amplified by 76.5 times and the final output is 15.3mA (actual)
 - The configuration amplifying component resistors (510, 39K)
 - Connection configuration relay operation time (25ms ~ 250ms)
 - Connection diagra

3) Questions
 - Is the current amplification output of OPA 602 1EA limited to 10mA?
 - Is this the part that needs more than the relay operation time to the output of the current amplification?
 - Is there any other configuration that I can configure other than the above?

  • Hi BJ,

    to fully answer your question a complete schematic of your circuit would be needed.

    Try to understand how the circuit works: The current source drives a current of 100µA through R1 and produces a voltage drop. The OPAmp tries to force a current through R2 until the voltage difference between the both input terminals of OPAmp becomes zero. Because of that, the voltage drops across R1 and R2 are equal.

    But what absolute voltages will be present at the input terminals and output terminal of OPAmp depends on what you connect to the + input of OPAmp! And now comes the limitations of OPAmp into play: The OPA602 has a limited input voltage range and a limited output voltage range. Please have a look at the datasheet specifications on page 3. If these limits are violated, the circuit will no longer work as desired.

    Kai
  • Hi Kai,

    I would like to make further inquiries on the following statement.
     
    1) Answering the following
      - The applicable IC function is the resistance measurement function and "Resistance to be measured" is connected to + input of OPAmp side
        The resistance to be measured ranged from 1Ohm to 1KOhm / 0 to 10, but we could measure the current shaking at 100 to 1KOhm
      - I do not know where the contents of the data sheet mentioned below are.

     2) Additional inquiries
      - I am guessing that the output of the OPA602 is limited.
      - I will edit and send the schematic you requested

  • Hi BJ,

    interesting circuit!

    I see the following issues:

    1.If you have a look into datasheet, then you will see, that the OPA602 can only handle an output current of +/-15mA guaranteed at +/-10V output voltage. Typically, it is +/-20mA. So, 20mA through R653 is a bit too high.

    2. The +input can only handle +10.2V guaranteed. Typically, it is +13V. So, when the voltage drop across the load resistance ("resistance to be measured") exceeds this level, the OPAmp stops working properly. This is the case when the load resistance exceeds 13V/20mA=650R (typically), or 10.2V/20mA=510R (guaranteed). So, your circuit cannot measure load resistances >650R (typically).

    3. The AQW214 has a typical Ron of 30R. The two switches in the AQW214 in series have 60R. This resistance is in series to the load resistance. So, even when the load resistance is 0R, you will measure 60R.

    Kai

  • Dear, Kai,
    Thank you for your attention and support.
    If you have any additional questions, I will ask again.
  • Hi BJ,

    Is it okay to close this E2E inquiry now?

    Regards, Thomas
    Precision Amplifiers Applications Engineering