ADS7961: Strategy for supplying power to A/D system

Thanks Tom's reply!

Sorry, SPI buffer/isolator is TXU0304 instead of TMUX0304.

The TXU0304 is a level shifter with both input/output sides having a common ground.  You will not have any 'electrical isolation' from the ADC input through to the Raspberry Pi if that is your intention (the dashed line).

Hi Tom:

I've read here

https://www.ti.com/lit/pdf/slla411

I think isolation is necessary for situations where grounding is not good (e.g. EV systems).

But my usage is in the hospital.

So the grounding of the Raspberry Pi and the A/D front-end is basically no problem.

So maybe I don't need really isolator IC such as ISO7741.

But level shifter is necessary because GPIO of Raspberry Pi is LVCMOS-3.3V and my SPI of ADC is LVCMOS-5V.

So level shifter such as TUX0304 is still necessary.

TUX 0304 also provide protection for unexpected behavior such as EDS problem.

Above is my understanding and are they right?

Best Regards!

De Wei

Well...that depends on how your circuit is interfacing with the patient.  Is the photodiode array connected in some way to a person?  If so, the IEC60601 standard is going to dictate what sort of isolation you will need for this application.

Hi Tom:

Our product is proton detector which is for calibrate proton beam.

We have a material(plastic optical fiber) that would be brighten when proton hit this plastic optical fiber.

Photodiodes, A/D front-end and Raspberry PI just tell us what the light intensity is from the material (plastic optical fiber).

So for the circuits(photodiodes, A/D-front-end, PI) are not contact with patient directly and leave patient far away.

Material(plastic optical fiber) would close to patient but not contact with  patient.

Regarding IEC60601, I quickly read a outline.

Most important thing of IEC60601 seems to be isolation of power.

That means patient can't be electrocuted.

Our PSU(AC-DC) has been passed by IEC60601.

And plastic fiber is a insulated material.

Best Regards!

De Wei

Hi Tom:

Thanks your suggestion.

At first, I thought that adding such a TUX0304 might help remove noise from the input signals.

TUX0304 seems to also provide protection I/O then, I don't need to add such clamp diodes to protect I/O.

You still don't recommend adding TUX0304?

Best Regards!

De Wei

I have no issue with adding it if you don't need the electrical isolation.

Ok! I got it. Thank you very much!