ADS124S08: Need help to review ADS124S08 for proper supplies and interfaces

Hi Lasto,

I'm not quite sure that I follow what all is going on.  Is the current B coming from a 4-20mA loop?  Is current A a diagnostic?

1. The effect of L10 will depend on the DC resistance value of the ferrite.  If the current is constant, then the ferrite should have little effect on the shunt measurement.

2. As to the input filtering, the only value of resistance I see in the filter path is the wiring path and RN1.  I don't see a value for RN1  There are a couple of considerations.  One is with respect to anti-aliasing and/or noise filtering to create a low-pass filter.  The other consideration is current limiting for transient events.  The analog inputs must be prevented from an over voltage condition where excessive current can flow through the analog inputs.  10mA is the maximum.  It appears that you have a TVS diode on the B current side to clamp the voltage.  The schematic shows 5V, but the voltage that can be dropped is usually higher.  Even if the over voltage is 5V, this is 2.2V over the maximum input voltage (AVDD+0.3V).  So current will flow through the ESD structure to AVDD.  This would require a voltage drop across RN1 to limit the current to no more than 10mA.  2.2V/10mA is equal to 220 Ohms minimum resistance.  Most likely the voltage at the TVS could potentially be several volts greater than 5V, so the resistance would probably need to be larger.

3. The supply/ground connections appear to be ok.

4. EMI/EMC is always a challenge.  Generally you would want to avoid all splits, especially in ground layers.  This would mean having a common, single ground plane.  Isolation requirements prevent this ideal situation.  Alternating signal and ground layers is also helpful, but this can greatly increase the total number of layers and cost of build.  You may also want to refer to the information in this FAQ post:

https://e2e.ti.com/support/data-converters/f/73/t/755516

Best regards,

Bob B