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Using a OPA2209 as a DC signal Amplifier

Jose F. Hernandez
Prodigy 50 points
Other Parts Discussed in Thread: LM324, LM358, OPA2209, OP07, OPA365, OPA333, OPA378, OPA350, OPA320, OPA340

Hi, few months ago I bought some OP2209, I did it for the purpose of implemented as a DC signal Amplifier.

I chose it because have a single supply alimentation (in my application I need to use USB alimentation) and the other features that make it a great OpAmp.

In my country I can only find old models of OpAmp (741, lm324, lm358...) but I need the best results that may have.

I want to use the OPA2209 as a Non-Inverting Amplifier but I can´t find a circuit that can provide me a good behavior.

I read the SLOA076 but I don't understand which circuit I have to implement.

In the past I used the OP07 (as a non-inverting amplifier, gain 11, and works great) but now I need to feed the OpAmp with Single Supply (like USB, +5V an Gnd). I did the Non-interting amplifier configuration with resistors values 1kOhm and 10kOhm.

This one is my old configuration that works fine.



Thanks, I hope you can help to solve my situation.

Best Regards.

  • 0
    TI__Guru 60570 points

    Jose,

    OPA2209 is not optimized for a low voltage, single supply application you seem to require - its input common-mode voltage range extends 1.5V from either rail while its output has a linear range 200mV from either rail - see PDS table below.  What it means is that on 5V supply, the valid common mode range, Vcm, is from 1.5V to 3.5V resulting in the output of 1.5V*11=16.5V to 3.5V*11=36.5V, which, of course. is not possible on 5V supply.  In the gain of +2, you could use OPA2209 from 1.5V to 2.4V resulting in an output from 3V to 4.8V (upper output range).

    If you reference the input to mid-supply (V1=2.5V), your valid input range in gain of +11 would be from ~2.3V to 2.7V - see below.

    For a single supply 5V application, you should use one of our rail-to-rail op amps like OPA320, OPA333, OPA340, OPA378, OPA350, OPA365, etc.

  • 0 in reply to Marek Lis
    Prodigy 50 points

    Hi, Mr Marek Lis, Thank you for your quick answer.

    What can I do with the OPA2209 to try to make it work with my application? (if you can, please give me an schematics).

    Is the only solution change it to another model?

    Thanks in advance.

    Best Regards.

  • 0 in reply to Jose F. Hernandez
    TI__Guru 60570 points

    Jose,

    In order for me to help you with your circuit, I need to understand what is it exactly that you need; it is not sufficient to say "I want to use the OPA2209 as a Non-Inverting Amplifier but I can´t find a circuit that can provide me a good behavior" as this is not specific enough (this does not tell me what is the input signal range you try to amplify.

    For example, for Gain=+1, Vsupply=5V, you may use OPA2209 in a follower configuration as long as the input voltage range, Vin, is within 1.5V to 3.5V - see below.

    For Gain=2, you may either use the circuit with RIN grounded (see below) for 1.5V<Vin<2.4V resulting in the output range, 3V<Vout<4.8V

    or you may use the circuit with RIN biased at mid-supply (see below) for 1.35V<Vin<3.65V resulting in the output range of 0.2V<Vout<4.8V

    I do not want to show here each possible gain combination but the bottom line is that in order to use OPA2209 with Vsupply=5V you need to make sure that the input voltage is between 1.5V to 3.5V AND the output range is within 0.2V to 4.8V (PDS specifications).  Therefore, for higher gains, the valid input voltage range gets smaller and smaller so the output does not exceed PDS limits as shown above.

  • 0 in reply to Marek Lis
    Prodigy 50 points

    Thanks again for your answer,

    With the circuit shown above (with the OP07) I have the range, min 0V and max 0,8V (output amplified by the OP07).

    I use a LDR sensor as a light sensor (light intensity), the sensor directly gives a small DC signal proportional to a light intensity.

    The amplified signal goes to an MCP3201 ADC which is finally connected to a PIC12F683.

    The gain of +11 that I used is because I get very good results with the OP07 and I appreciate very well the behavior of the changing light intensity.

    I changed the OP07 for the new OPA2209, for the simple reason that have very good features and can feed it with a single supply (and it´s better than the OP07).

    If you need more information in order to help me, please let me know.

    Thanks,

    Best Regards.

  • 0 in reply to Jose F. Hernandez
    TI__Guru 60570 points

    Jose,

    Since there is no ground inside op amps, any op amp may be used in a single supply or dual supply configuration.

    Therefore, you have a greater input voltage range with OP07 than OPA2209, not because its input common-mode extends closer to either rail than OPA2209 but because you use OP07 on dual supply +/-5V while OPA2209 on single 5V supply - that is unequal comparison.

    If you look at the OP07 PDS (see below), its input common-mode voltage range is 2V from either rail (in case of OPA2209, it's 1.5V).  Also, while the OPA2209 output can get withn 200mV from either rail, OP07 can swing only 3V to either rail - much worse than OPA2209.

    In short, if you use OP07 the same way you attempt to use OPA2209 with single supply 5V, you would find out that its input range would be only from 2V to 3V while its output range would be none since it would take a minimum of 6V supply in order not to violate OP07 linear output range of 3V from either rail.  This compares to OPA2209 better input range of 1.5V to 3.5V and much wider 0.2V to 4.8V output voltage range.

    Therefore, with the circuit as shown below, you would not have the input range of 0V to 0.8V, as you claim, since this would require the output to swing to 8.8V - impossible on +5V supply (Vout=Vin*Gain=0.8V*11).

    Since the OP07 output may swing only +/-2V on Vs=+/-5V (see PDS table above), your input range would be only: Vin=Vout/Gain=+/-2V/Gain=~+/-180mV.

    Similarly, if instead you use OPA2209 in the same configuration, its input range would be Vin=+/-4.8V/Gain=~440mV

  • 0 in reply to Marek Lis
    Prodigy 50 points

    Hi, Mr. Marek Lis, thanks again for the guidance and patience to help me.

    I think I explain myself bad about my input range.

    The entry that I have from the sensor is in the range of 0V to 0,08V (When this input goes through the circuit OP07 above, I have an output range between 0V to 0,8V).

    The input that I want to handle is really small.

    Another thing that I think can work is:

    There is any way to do a Dual Supply from a USB supply? The DataSheet says the operation supply goes to +/-2,25V to +/-18V. If I can split the 5V of USB port into +/-2,50 I think I can resolve the situation.

    Thank you,

    Best Regards.

  • 0 in reply to Jose F. Hernandez
    TI__Guru 60570 points

    Jose,

    Yes, you could level-shift the reference voltage to 2.5V mid-supply (see schematic below) and effectively create a dual-supply from your USB port.  However, even if you do this, your 80mV input voltage range would result in 0.8V output superimposed on top of 2.5V, resulting in the output voltage of 3.3V - see below.  But the OPA2209 output voltage range is specified 2V or more from either rail and thus 3.3V on Vsupply of 5V would violate this condition as this would result in the Vout of 1.7V from the positive rail (5V-3.3V).

    All in all, I believe you need to seriously look into using another part (rail-to-rail) in your application as I recommended before: OPA320, OPA333, OPA340, OPA378, OPA350, OPA365, etc. since OPA2209 with input and output voltage range of 2V or more from either rail is poorly suited for your specific application requirements.

    You may be able to recieive some free samples of the devices by requesting them on TI website.

  • 0 in reply to Marek Lis
    Prodigy 50 points

    Hi Mr. Marek Lis, Thanks for all your help.

    Finally I will attend to your advice, use another part. It's better for my application.
    How can I do to get some samples of each parts that you recommend me?
    I'm in venezuela, but usually when I buy stuff in Mouser, Amazon, Digikey, etc., I send to miami to a cargo company and then they send me (to venezuela) all what I sent them.

    Thank very much, I appreciate.

    Best Regards.

  • 0 in reply to Jose F. Hernandez
    TI__Intellectual 1165 points

    Hi Jose,

    You can order free samples of the devices Marek mentioned through ti.com.  Just search for the product in the search box, and when you get to the product folder, click on "Sample & Buy", then click on "Free sample" to add the sample to the cart, and when you are finished adding all of the samples you need to your cart, you can place the free order to be shipped to Venezuela.

    Best Regards,

    Marc