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

Hello Krishna,

Thank you for your post. For this design, in order to get the output you require, it's not enough to just change the amplifiers and the supply voltages. Values for all passive components need to be readjusted for the new input/output requirements. The design guide describes the equations needed for Rset, Rload, R1, and more: http://www.ti.com/lit/ug/slau507/slau507.pdf

Please follow this procedure, good luck moving forward.

-Tamara

Dear Tamara,

Thank you for the reply. I found the SLAU507 doc very helpful. I have tried to follow the instructions in the doc and do some simulations, but still I am finding it difficult in choosing the correct INA.

I have attached two Tina simulation docs.

In the V-To-I_12V_OPA735_INA326 doc, the output is linear enough till 4.99V, at 5V it is saturating to 993uA o/p.

In the next iteration I changed the INA to INA128, and tried to set gain for 1 and 10, the current output is saturating for 1V and is not linear.

Please help me choose a correct INA and give me proper linearity.

Thanks & Regards

KrishnaV-To-I_12V_OPA735_INA326.TSCV-To-I_12V_OPA735_INA128.TSC

I think you are violating the I/O headroom requirements, your file did simulate showing this, 

And from the datasheet, input headroom required

And output headroom, 

If I go +/-5V on the OPA725 and -5V +15V on the INA128, it is better, but still clips on the high side, 

Dear Michael,

Thank you for simulating and highlighting the clipping of the signal. If I need to modify the TIPD107 circuit to a one complying with 12V then what is the type of INA and OPA  I need to choose, so I don't get the clipping.

- Krishna

Dear Tamara,

Thank you for the reply. I found the SLAU507 doc very helpful. I have tried to follow the instructions in the doc and do some simulations, but still I am finding it difficult in choosing the correct INA.

I have attached two Tina simulation docs.

In the V-To-I_12V_OPA735_INA326 doc, the output is linear enough till 4.99V, at 5V it is saturating to 993uA o/p.

In the next iteration I changed the INA to INA128, and tried to set gain for 1 and 10, the current output is saturating for 1V and is not linear.

Please help me choose a correct INA and give me proper linearity.

Thanks & Regards

Hi Krishna,

I'm working on this one. Can you clarify the input voltage range? Did you want Vin = 0.0049V to 4.9V? Or did you want 0.0099V to 9.9V?

Your previous post said (0 to 10V), but the schematic says (0.0049V to 4.9V).

-Tamara

Dear Tamara,

Thanks for the update. The larger the input range, lesser the resolution of input required for each step. So better I need 0 to 10V.

Sorry I forgot to edit the text in the schematics.

Thanks

Krishna

Hi Tamara,

Any updates, were you able to find some solution?

-Krishna

Dear Tamara,

Thank you for the simulation results and introduction to a new concept which I was unaware of, I shall test the circuit practically and get back to you on the same.

Thanks & Regards

Krishna

Hello Krishna,

Great! I'm going to close this thread for now. Feel free to reply to re-open if you have any questions moving forward.

-Tamara