1Khz Constant Current Source

Hello Shihab,

Have a look at the OPA172 and OPA192 data sheets. These two amplifiers will likely be able to provide the peak current of 25.5 mA, operate over the required temperature range, and have very good dc and ac specifications.

http://www.ti.com/lit/ds/symlink/opa172.pdf

http://www.ti.com/lit/ds/symlink/opa192.pdf

Regards, Thomas

PA - Linear Applications Engineering

Thank you Thomas.

Is it possible to get an opamp which will consume less current than OPA172&OPA192.

I am looking for an opamp which has supply current <500uA.

Regards,

Shihab.

Hi

I have downloaded the OPA172 and OPA192 spice model from Ti website and used in Ltspice. I made a non-inverting amplifier of gain=2 and checked the Open loop gain graph. The model do not behave as per the datasheet. Please let me know if the model is correct or not? I have attached the Spice model and also the screen shot of the circuit simulation.

6622.sbom854.zip

Hello Shihab,

I am unable to open your OPA172 test circuit pictures. Can you either attach them as an image file, or insert them in your response using the "insert image" icon in the row show above? the icon sort of looks like a white picture frame with a green sphere in the middle.

The OPA172 and OPA192 models were tested with Penzar TopSPICE. Its Spice syntax is compatible with Cadence PSpice. I do believe the syntax should be compatible with LT-Spice.

Regards, Thomas

PA - Linear Appliactions Engineering

Hi Thomas,

Please find the attached folder which contains the LIB files of OPA172 and OPA192.

The simulation files to do the AC analysis is also included.

I would like to know why I am getting a loop gain which starts from -ve value.

7824.New folder.zip

Thanks,

Shihab.

Hi Shihab,

I checked your OPA172 circuit using TopSPICE. I had problems with the simulation as well. It turns out that the OPA172.txt file listed on the web page has many IC=0 (initial condition = 0) settings after component values. We have found this causes problems in some circuits with some simulators.

I went throught the file and removed all the IC=0 statements. Your circuit simulated as it should. I expect you will have the same result with your simulator. I have attached a new OPA172.txt file. It has the IC=0 statements removed.

If you decided to try the OPA192 model it does have the IC=0 statements. You would want to use the "find" function in the text editor and remove them. The resave the file with the extension required for your simulator.

Regards, Thomas

PA - Linear Applications Engineering

Thank you Thomas, it worked.

Hi Thomas,

I am considering one more opamp for my application, TLE2161AMD, due to its low Quiscent current than OPA172. Is this commercially available. From the datsheet I could see this part (SOIC-8 -55degC to +125degC). But I could not see the availability of this part.

As per the datasheet of TLE2161 it is stable for gain >= 5. I did AC analysis of non inverting amplifier (gain=2) with this opamp and found to be stable. I expected it to show unstable at gain of 2. Why this behaviour? is it ok?

I have attached the simulation file.

Thanks.

4403.New folder.zip

Hi Shihab,

The TLE2161AMD would be a military temperature range device handled by the Military/Hi-Rel group in TI. A search for the TLE2161AMD in the TI system did not reveal any links to the deivce. That indicates to me that the device was likely obsoleted. There is a High-Reliability E2E forum where you could inquire further about its availability.

When I review the TLE2161 simulation model syntax I find it has a1990 development date. It uses a much simpler Boyle model for the operational amplifier structure. That model lacks the sophistication you find in the modern models being developed today. It doesn't include the complex open-loop output impedance characteristics which are needed for an accurate stability analysis. Therefore, you can't rely on the TLE2161 model to give you an accurate indication of stability. 

The OPA172 and OPA192 simulation models do include the complex open-loop output impedance characteristics allowing for accurate stability assessment of amplifier in circuit of interest.

Regards, Thomas

PA - Linear Applications Engineering

Hi John,

I attach the OPA192.LIB and OPA.asy  files that I have. For me this is working fine.

-Shihab.OPA192.zip