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Questions about HMC794LP3E


My customer is considering to use HMC794LP3E and ask some questions about the function of U9 in evaluation schematic(Page 9 , Page 10 of HMC794 Datasheet).

Please reter below schematic and let me know your opinions about their questions.

Q1) What is the function of U9?

       Is it only the converting LDO from 5.5V input to 5V output?

Q2) If the needed funtion of U9 is a voltage down conversion from 5.5V to 5V, could they connect a 5V source to HMC749 directly without  using addition LDOs (same as U9)?