Isolated DC/DC converter acceptable to generate Vreg?

motron said:

Can I use a isolated DC/DC converter like Recom RSK-2405SRUW/H3 to generate Vreg for ADBMS1818?

Yes you can, as long as VREG is between 4.5-5.5V and can source enough current you can use any supply on the VREG pin.

In the schematic attached, I used the RSK-2405 (ignore the part number), removed Q1I,  and I did measure 5V at TP4I(Vreg) but when requested measurements via serial interface, the input pins all read zeros.  Is there some pin setting that need to be changed?  By the way, I know the DC/DC converter isn't truly isolated.  Just a quick test.

Do you supply VP with at least 16V and made sure the converter can source enough current for the AFE? 
It might also be that communication is not reaching the AFE, did you get correct reading when using the NPN before?

No on the 16V.  I have only 7 cells on this IC.  But the DC/DC was putting out 5V.  I did get the correct reading with the NPN but that was with cells on all inputs.  I normally get comms and reading when VP is around 13V.  I know that isn't to spec.

motron said:

No on the 16V. 

We cannot confirm the IC will operate below the minimum specs. 

motron said:

I did get the correct reading with the NPN but that was with cells on all inputs.

So in this case VP was beyond 16V, thus the correct operation.  

OK.  Can I power V+ with a source other than the top cell voltage?  Generate V+ with a DC/DC converter boosting the voltage above the 16V threshold with its input from the seven cells?

Any comments on my last post?  I would like to move forward on this issue.

motron said:

OK.  Can I power V+ with a source other than the top cell voltage?  Generate V+ with a DC/DC converter boosting the voltage above the 16V threshold with its input from the seven cells?

What kind of cell is this? Does the minimum voltage of these cells go below 17V when 7 cells are in series? 
If yes then it makes sense to design a DC/DC converter for boosting the voltage. If not you can connect V+ to top most channel.