ZHCSIK3 July 2018 TPS650861
PRODUCTION DATA.
This device is designed to work with several different input voltages. The minimum voltage on the VSYS pin is 5.6 V for the device to start up; however, this is a low power rail. The input to the FETs must be from 4.5 V to 21 V as long as the proper BOM choices are made. Input to the converters should be between 3.3 V and 5 V. For the device to output maximum power, the input power must be sufficient. For the controllers, VIN must be able to supply sufficient input current for the output power of the application. For the converters, PVINx must be able to typically supply 2 A.
A best practice here is to determine power usage by the system and back-calculate the necessary power input based on expected efficiency values.