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  • TI Thinks Resolved

INA326: INA326 REF 200

Prodigy 35 points

Replies: 5

Views: 61

Part Number: INA326

Hi, i am looking for a current source in the range of nano amperes, my working current range is 10n Amp to 500n Amp of current source. I saw you provide an IC REF 200 but the output current of this ic is still high for my application. Do you have any solution regarding my application. Or any idea how i can use REF 200 to get an output in my desired range.

Thank You

  • Hi Mannan,

    Enclosed are links about how to build V to I converter.  

    https://www.ti.com/lit/an/sbva001/sbva001.pdf

     https://www.ti.com/lit/ug/slau507/slau507.pdf

    The REF102 and REF200 are legacy devices, and I am not sure that they will work well for your current range. BTW, How precisely do you want your 10nA to 500nA in current source?

    I found the following current source circuit that might work for your application. It claimed that it has <10pA error out of 1nA in accuracy (total error < 1%). I have not had a chance to simulate in Tina. If you are interested, please let me know. We may have to use lower Vos and higher precision op amp to achieve the precision in the current source application. 

    Alternatively, you may build current source out of discrete matched Mosfets or BJTs in current mirror circuits, which are used inside of IC or REF200. Because of the low current levels, it may be more difficult to make it practical with discrete components.

      

    Best,

    Raymond 

     

  • In reply to Raymond Zhang1:

    Hi Raymond 

    Thank you for your reply and sending me the circuit and pdf's of V to I converter. My application does not require a high precision current source, the only constraint which we have is the low amplitude current source. I would be grateful if you can simulate the circuit and we can see how much is the output current and voltage drop across a resistive load of about 10M ohm. 

    Thank you
    Best Regards

    Mannan

  • In reply to Mannan Ab:

    Hi Mannan,

    Here is a working version of 10nA to 500nA constant current source with total error <1%. I changed the circuit with OPA192 instead of OPA376, though both op amp are equally comparable (no particular good reasons for the change, both will work for your application). 

    The current load R11 has to be <= 1/1000 of R10 or 10MOhm in order to keep the error low. Vin needs to be from 100mV to 5V in range to generate 10nA to 500nA output current. 

    Enclosed is the Tina simulation. 

    If yo do not like -2.5V negative rail, you may use LM7705 to generate -0.232V from positive regulator voltage, see the simulation below. 

    /cfs-file/__key/communityserver-discussions-components-files/14/OPA192-10nA-to-500nA-Current-Source-1-percent-08122020A.TSC

    If you have any additional questions, please let us know. 

    Best,

    Raymond

  • In reply to Raymond Zhang1:

    Hi Raymond

    Thank you for helping me to send the simulation of the circuit, so far the output looks good. I will order the components and assemble the circuit to test the circuit. If i face any issue definitely i will get back to you.

    Thank you

    Best Regards

    Manan

  • In reply to Mannan Ab:

    Hi Mannan,

    is your load actually 10M? The voltage drop of 500nA across 10M would be 500nA x 10M = 5V. Is this what you want?

    Kai

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