TINA/Spice/OPA189: TINA-TI MACRO BUG?

balazs buglyo

Part Number: OPA189
Other Parts Discussed in Thread: TINA-TI, OPA827, , THS4551

Tool/software: TINA-TI or Spice Models

Hi There.

Can someone help me about the followings:

I have a TINA-TI simulations with OPA827 and i want to change it to OPA189.
Can i change it?
I want to use it for only DC signal i dont need to measure any highspeed signal or fast changes.

if i change it the simulations show very unaccaptable data.

over 6 years ago

0 Ian Williams over 6 years ago

TI__Mastermind 27715 points

Hello balazs,

I'd be happy to take a look at your circuit. Can you please describe the problem you're having, and also attach your TINA .tsc file?

Your intention is to create a fully-differential circuit with VG1 as the input and VM1 measuring the output, correct?

Best regards,

Ian Williams
Applications Engineer/SPICE Model Developer
Precision Amplifiers

0 balazs buglyo over 6 years ago in reply to Ian Williams

Prodigy 230 points

Dear Ian,

Thank you for your replay.
I will send my Tina tsc files today.
Yes i would like to do it but i missed the THS4551 from the picture.
I checked the datahseet of OPA827 and OPA189 maybe i missed something but it seems more or less the same where i would like to use it.
Dc signal measurement nothing more, at low freq.

Regards,

Balazs

0 balazs buglyo over 6 years ago in reply to Ian Williams

Prodigy 230 points

I attached the TINA-TI files for you.
You can simply check them.

There are 3 files.
opa827+ths4551 -> this is what i want to get with opa189. -> Run the DC transfer on it.
Next you can find the ideal opamp test with opa189 and opa827 -> if you run the DC transfer for VG2 and select the VF2 VF3 and VM2 you can check the ideal.
if you run it for the VG3 you will get it for opa827 it has some offest but it can be good for us.
But for VG1...
opa189+ths4551 you can get the something not good.

Maybe i missed something in the datasheet, it can be , but if you can check it for me i will be very greatfully.

Regrads

Balazs

sim.rar

0 Ian Williams over 6 years ago in reply to balazs buglyo

TI__Mastermind 27715 points

Hello Balazs,

The issue here is caused by how you've connected the input signal. The way your circuits are drawn, the op amps inputs have no DC path to ground. Depending on the way the op amp SPICE model is designed, it will either a) work fine, or b) go into input saturation as the floating input charges to some voltage dependent on the input bias current and the input capacitance. In this case the OPA189 is behaving like option b.

What I recommend in this case where you desire a differential input signal is to use two VCVS to convert the single-ended input source to a true differential signal with a proper ground reference. If you do this, like in the examples I've attached, the OPA189 performs correctly and we see the offset voltage appear at the output.

OPA189+THS4551_iw.TSC

test_opa189_and_opa827_and_idealOpa_iw.TSC