Although it is optional, it is always recommended to have a PMBus connector to connect the Fusion GUI. You may need this connector to program the device. It also comes in handy when you need to debug the board and adjust configurations. Unlike analog devices, the UCD90xxx provides full visibility to the internal status of the device. It helps you analyze complex sequencing logics and identify problems quickly.
For more FAQ please check the following document.
UCD90xxx Family Frequently Asked Questions and Answers
UCD9090 UCD9090A UCD90120 UCD90120A UCD90124 UCD90124A UCD90160 UCD90160A UCD90240 UCD90320 UCD90320U