ISO224: Hardware review_ISO224BDWVR

Hi Manjunath,

I don't immediately see anything wrong with your schematic, but I wanted to make sure you are aware of the fact that the ISO224 attenuates the input signal by 1/3.  Your (assumed +/-5V) input signal is going to be +/- 1.6V on the output.  Is that what you are looking to do?

Hi Tom,

Thanks for the quick review comments.

Application requirement is : Analog input from an External sensors can be from 3.3V to 12V, Ex:For 3.3V Input Differential Out is +/- 1.1V and for 12V output is +/-4V. This is fine for me.

Please review the schematic after Differential output signals which goes to "TLV9001IDCKR" Op-Amp which I used for buffering.

circuit design of this Op-amp since I'm new to circuit design, need your help.

Thanks

Tom,

Kindly reply

Hi Manjunath,

So here are a few observations after spending a little more time with your schematic.  The ISO224 needs 5V power on both sides to the chip, your 3.3V rail on VDD2 has to be at least 4.5V (datasheet section 7.3).  With a single supply opamp on the differential to single ended output stage, you need to add some bias voltage to level shift the output.  You can see an example of how to do this in the ISO224EVM Users Guide.

Hi Tom,

Gone through all the technical documents, By refereing to "https://www.ti.com/lit/an/sbaa317/sbaa317.pdf" document I updated the schematic.

Please review.

Application requirement.

3.3 V to 12V Analog input signal should be sensed. So resistor values in the schematic is selected according to that.

and Output voltage should be 3.3V

So Please check the attached schematic.

and one more question is adding some filter components near Op-Amp, Please suggest these components also if require.

Thanks

Hi again Manjunath!

SBAA317 is a great document, Alex did a nice job with it.  One key point you are missing though is that little 1.65V Vcm term on the end of R1 below the Design Description paragraph.  His TLV9002, like your TLV9001, is powered from a single 5V supply.  You need that Vcm term to level shift the output above ground, otherwise the amplifier will saturate when your input goes below GND1.

The Rfilt and Cfilt components shown in that document are better described in a video on driving SAR type converters.  You can find that video series here.  Section 6 describes picking the filter components.

Hi Tom,

We don't have this scenario of input going below GND1 level (Always varies from 0V to 12V). So in that We can connect to GND right ?

Hi Manjunath,

OK, sorry for the misunderstanding - let's go back to the SBAA317 document using your 0-12V input case.  With half the full scale range applied to the input of the ISO224, you will only get half of the full scale output from the device.  So 0-12V in gives you +/-2V differential, centered on the common mode voltage of VDD2/2.  You could keep the resistors ground referenced, but you would need to adjust the gain accordingly.  You would still see a little clipping on the output with 0V in as well.  You might consider downloading TINA-TI (it's free!) and use it with the example circuit Alex provided in the Design References section of SBAA317

Hi Tom,

After all going through the TI documents and study on the Isolation amplifier.Updated the attached two circuit which are simulated TINA TI.

for both 3.3v and 12V which varies from 0.9 to 3.3V, This is fine for us. I don't want to have an additional 1.65V power supply. SO changed R3 & R4 to 5K.

SO please review 

Great!  Let us know how you make out in the end.