Use of ISO224 as analog isolator

[LeanSol345]

Hi, I’m using ISO224 to isolate analog signal from a sensor (e.g. Temperature/Humidity sensor) for Raspberry Pico ADC (analog pins). As per my understanding, IC has 2 output pins (Inverting & Non-inverting). Can I use only single pin (Non-inverting) for output and ground the other so that the Gain should be unity.

Please mention if there is any other alternative ICs for the application.

 

[KlausST]

Hi,

I don't have the datasheet by hand ... so I can't consult it.

But generally you never short any output unless it clearly is mentioned.

Please mention if there is any other alternative ICs for the application.

An application is "defined" by values with units ... and tolerance.
Like power supply voltage(s), timing, interface type, signal frequency, signal levels (or range), noise, drifts, accuracy, precision, .... and so on.
We have nothing ...

Klaus

 

[LeanSol345]

The purpose is to simply isolate Raspberry Pico analog pins (Not exceeding 3.3V - I don't know Max handling current value of ADC of Pico). While there are analog sensors that might give output up to 5V, 24V or 4-20mA. I just want to control spikes/surges from any sensor as it should not cross the ADC limits. Need help or clarity if there is misunderstanding in concepts.

--- Updated May 16, 2024 ---

Hi,

I don't have the datasheet by hand ... so I can't consult it.

But generally you never short any output unless it clearly is mentioned.


An application is "defined" by values with units ... and tolerance.
Like power supply voltage(s), timing, interface type, signal frequency, signal levels (or range), noise, drifts, accuracy, precision, .... and so on.
We have nothing ...

Klaus

 

[stenzer]

Hi,

I agree with @KlausST do not short the output, especially here with a differential output. A unipolar supplied opamp with a differential output requires a common-mode output voltage. Here, this common-mode output voltage is provided by the ISO224 itself. So here you would short this mode output voltage, by means of VDD2/2 to GND.

In figure 48 you see a solution how to deal with the differential outputs to be used by a single ended ADC.

BR

 

[LeanSol345]

Hi,

I agree with @KlausST do not short the output, especially here with a differential output. A unipolar supplied opamp with a differential output requires a common-mode output voltage. Here, this common-mode output voltage is provided by the ISO224 itself. So here you would short this mode output voltage, by means of VDD2/2 to GND.

In figure 48 you see a solution how to deal with the differential outputs to be used by a single ended ADC.

BR

So you mean it can serve the purpose (transfer same analog signal) but will need external circuit as in figure-48?

 

[stenzer]

TI recommends it, so I would use it. But most likely a resistor limiting the output current will work as well. The ADC itself would also represent a high ohmic load.

Can you show us a sketch of your measurement system? Are you using the ISO224 as isolation barrier between a high voltage and low voltage area?

BR

 

[KlausST]

Hi,

I just want to control spikes/surges from any sensor as it should not cross the ADC limits.

Correct me if I'm wrong. You use an isolation amplifier just for ADC input protection?

If so, I never in my decades of designing circuits for rough industrial environment had such an idea.
For "protection" I use protection circuits and parts. There are plenty.
For "isolation" I use isolation circuits and parts.

Klaus

 

[FvM]

ISO224 is specifically designed to drive differential ADC. There are several isolation amplifiers from TI and other vendors (e.g. ADI) with single ended output, check vendor and distributor search engines.

--- Updated May 16, 2024 ---

I agree with KlausST that isolation amplifiers would be only used if galvanic isolation is required. It involves also isolated power supply.

 

[stenzer]

I agree with KlausST that isolation amplifiers would be only used if galvanic isolation is required. It involves also isolated power supply.

That's the reason why I asked for a system sketch, as it doesn't sound like an galvanic isolation topic.

 

[LeanSol345]

Hi,

Correct me if I'm wrong. You use an isolation amplifier just for ADC input protection?

If so, I never in my decades of designing circuits for rough industrial environment had such an idea.
For "protection" I use protection circuits and parts. There are plenty.
For "isolation" I use isolation circuits and parts.

Klaus

Alright then I think I was at the wrong track. Please share a protection circuit example or calculation method as the microcontroller is Raspberry Pico of ADC 3.3V.
Thanks

 

[KlausST]

Hi,

* define your signal you want to measure
* define your signals to protect against
* define the limits of the RPi
* then do a search for protection devices / protection circuits according the above specifications.

Example:
If you want to protect against ESD, according HBM then you will find a lot of devices... then refine your search....

Klaus