TIPD107: Need to modify the circuit for 12V compliance voltage

Hi Tamara,

Thank you for the immediate reply. As you have said earlier, the XTR111 integrates the TIPD102 design, and the TIPD102 is not working as described.

https://e2e.ti.com/support/amplifiers/f/14/t/837502?tisearch=e2e-sitesearch&keymatch=%25252520user%2525253A421516

And also in the post : http://e2e.ti.com/support/amplifiers/f/14/t/837481?XTR111-2EVM-1uA-accuracy-with-modifications-in-the-circuit, you have mentioned that

" this FET's errors can change with device and temperature. These errors will add up and not allow you to guarantee the 1uA accuracy. " So the XTR111 ckt is out of consideration.

Next In the below thread you gave me a solution suggesting the Howlands current pump circuit

https://e2e.ti.com/support/amplifiers/f/14/t/837428

I am happy with the circuit. On the output side as well the voltage varies from 0 to 10V, but actually what I want is - Irrespective of the load the current should be proportional to the input voltage. But as we have seen in the howlands circuit, if I vary the load, the current also gets varied.

I have an app. note: SBOA233 in which the current is varied from 1uA to 10uA by just changing the input voltage from 0.49V to 4.9V; even if we change the load the current remains constant. This can be seen in the DC simulation results table of the document.

Please go through this calibrator datasheet: https://cdn.tmi.yokogawa.com/GS_CA71_E.pdf

The Page 3 Specification says : 

 DC Current: Range : 0 to 24mA; Resolution : 1uA; Maximum Load: 12V, so its a constant current source irrespective of the load it can drive 24mA of current at 12V; i.e. say it can drive a max of 500R load with 24mA.(12V/24mA)

Similarly in our case it is

DC current range: 0 to 1024uA ; Resolution: 1uA; Max Load: 12V. i.e Compliance voltage of 12V irrespective of load.

Thanks & Regards

Krishna

Hi Tamara,

Please let me know if you are working on it. Please update me at the earliest.

Regards

Krishna

Hi Tamara,

The voltage at the INA is only varying from 0 to 10V, but the voltage at the OPA is not varying similarly as shown in the SBOA233 diagram.

Now I am trying to implement 0 to 12V input and VOPA max as 0 to 12V, as VOPA max should be proportional to the input. current being the same 0 to 1024uA. 

I changed the supply to 15 and -15V wherever required and other parameters required as per the Application note formula to check 0 to 1024uA output for 0 to 12V input. I am not being successful.

Kindly guide me for the same.

Regards

Krishna

Hi,

Any updates?

Regards

Krishna

8863.0-10V in, 0-1024uA out.TSCHi Tamara,

I want to improvize on this

"

Hi Krishna,

I edited the design to fit your requirements. Since you want 12V compliance, we needed to switch out the Op Amp and the Instrumentation Amp with 12V options. The unique feature of the INA326 in the initial design is that it can swing to the rail on the output. All of our higher voltage instrumentation amplifiers cannot do this. So, you would need to provide a negative supply in order for this to work. 

I used the OPA188 for the op amp, and the INA826 for the instrumentation amplifier. They are both high precision amplifiers. See the attached TINA file and a snapshot of the output. When the input is 0-10V, the output will be 0-1024uA irrespective of the load. 

0-10V in, 0-1024uA out.TSC

"

And not on TIPD107.

Kindly provide suggestions