Where can I find a complete datasheet of the NS7520, including a description of the registers?

From NS site. Register yourself and download the PDFs.

I looked at the NS site yesterday, but I only found a file called NS7520_datasheetv1.pdf. This file didn’t explain the registers. Or did you had the 7520_HRM.pdf earlier? Thanks for the hint.

Netsilicon support notified to send you the required doc.