Value of CONTROL1 is invalid for both 4400 and 4491. Bits 12-23 all need to be 0. Also, Bit 8 needs to be 1. https://github.com/Protocentral/protocentral-afe4490-arduino/blob/b3471f69df5ea16f04a367d22c6c8229e1e9f591/src/protocentral_afe44xx.cpp#L123 