I evaluate the AD7401A with a shunt resistor (Vishay PG CSM3637 - 2mohm) as a current sensor for a multilevel-inverter design in each phase.
From the datasheet, figure 23 I have learned the the potential on VIN- of the AD7401A should normaly be attached to GND-potential and VIN+ can be between -250mV to 250mV below and above.
As the CSM is 4 pin device it is not sure in my case, that the sense pin for VIN- is realy on the same potential as the current sense potential attached to the floating "GND"-potential due to lead/contact resistance.
This can result finaly in some kind of commonmode voltage shift of the differential voltage across VIN+ and VIN-.
My questions are now :
How will this influence/degrade the performance of the ADC.
Is there a limit and in case where is the limit for such parasitic common mode voltage shifts of the differential voltage between Vin+ and Vin- with respect to GND.
( I would like to mention that the shift of the common mode voltage based on the parasitic contact resistance is depending on the measuered current and can switch sign depending on the direction of the current through the shunt resistor - i.e. it can also get negative ...)
I hope that I could explain the problem well enough. Please keep in mind, that the shunt resistor has only 2mohm - like this one can't simply neglect contact resistance here with respect to this common mode effect)
Addon questions :
1. Is it possible to use the ADUM5000 or ADUM6000 directly as a secondary side power supply for the AD7401A -or will it degrade the performance of the AD7401A because of noise/high frequency ripple ?
2. In the datasheet the AD7401A also voltage sensing is addressed by using a voltage divder network. But as the input resistance of the device is not characterized assumptions about voltage divider values are difficult without external buffer amplifiers. Can someone help out here and provide some data / information ?