ISO122: Isolating a 5V signal and reducing its scale to 1.8V

Manuel Chavez

Part Number: ISO122
Other Parts Discussed in Thread: ISO224

Hi Amplifiers forum,

Hopefully all is well. A TI customer is attempting to isolate a 0V - 5V analog signal and connect it to a 1.8V MCU input as in the block diagram below:

Is it possible to realize a system like this using ISO122? If so, please let us know which part numbers can be used in the attenuation circuit or feel free to share a schematic.

Thank you for your time,
Manuel Chavez

over 5 years ago

0 Alexander Smith over 5 years ago

TI__Guru 55232 points

Hi Manuel,

Is there a particular reason the customer is interested in the ISO122? It's an older device that requires bipolar power supplies. I would strongly suggest taking a look at the ISO224, the latest and greatest device in this family.

This cookbook circuit should help with the attenuation circuit: http://www.ti.com/lit/an/sbaa317/sbaa317.pdf

There are also additional documents under the technical documents tab that may help: http://www.ti.com/product/ISO224/technicaldocuments

0 Manuel Chavez over 5 years ago in reply to Alexander Smith

TI__Genius 17100 points

Hi Alex,

Thanks for your response. Our customer is looking for a unipolar input and output, so my recommendation came from the thought this can be achieved with ISO122 if its negative supplies are tied to ground. Is this incorrect or is there a better way?

Respectfully,
Manuel Chavez

0 Alexander Smith over 5 years ago in reply to Manuel Chavez

TI__Guru 55232 points

Hi Manuel,

Did you have a chance to look at the ISO224 as I mentioned in my last post?

Please see this document: http://www.ti.com/lit/an/sbaa311/sbaa311.pdf

0 Manuel Chavez over 5 years ago in reply to Alexander Smith

TI__Genius 17100 points

Hi Alex,

I did! The two-pin differential output is undesired by our customer since the signal is a unipolar MCU input. We are looking for an isolated analog signal buffer.

Thank you,
Manuel Chavez

0 kai klaas69 over 5 years ago

Guru 140200 points

Hi Manuel,

for me the ISO122 appears to be a bit outdated when I look at the ESD ratings. The ISO224, on the other hand, looks much more robust and can withstand much higher overvoltages. So, I agree with Alexander and would also take the ISO224 instead of ISO122.

Having said this, what is the isolation voltage specification of your customer? Must the customer's application withstand ESD, Burst (FFT) and Surge?

Kai

0 Alexander Smith over 5 years ago in reply to Manuel Chavez

TI__Guru 55232 points

Hi Manuel,

I see. Unfortunately we don't have a device that fits their exact needs, however a differential to single-ended conversion can easily be accomplished using a low-cost amplifier. This can be seen in the documents I've shown you.

Thank you as always Kai!

0 Manuel Chavez over 5 years ago in reply to Alexander Smith

TI__Genius 17100 points

Hi Alex, Kai,

Got it, thank you for your help!

Best,
Manuel Chavez