ADF4356 power supply rails

Question

I have a question about powering ADF4356. 
 I read this post https://ez.analog.com/webcast-qa/2018-webcasts/32218-best-pcb-layout-practices-for-frequency-synthesizers/f/q-a/78250/how-would-you-recommend-powering-the-many-power-rails-on-an-adf4356 
 And still have some questions so i bring it here. 
 With 5V rail all is clear. 
 What about 3.3V rail. 
 Datasheet says "For the 3.3 V supply pins, use two ADM7170 regulators, one for the DVDD and AVDD supplies and one for VRF. Figure 43 shows the recommended connections." 
 
 But as we can see one of the ADM7170 (VOUT) connected to DVDD and the other (VRF) to AVDD and VRF. 
 In evaluation board (EV ADF4356SD1Z) we have one power supply which generates all rails but still unlike datasheet pins AVDD and DVDD connected to one 3.3V rail (VDD) and VRF pins to the other 3.3V rail (VRF). 
 
 So, my question is does it make any difference which of the pins (AVDD, DVDD, VRF) we connect to the same 3.3V rail? 
 Which way is the right one, datasheet or evaluation board? 
 
 Regards, 
 yuri

ADIApproved · Accepted Answer

Hi Yuri, 
 I would suggest to isolate the VRF from AVDD and DVDD to prevent any coupling to be present at the output. You can use same source for AVDD and DVDD. 
 Regards, 
 Kudret)

Electronic Design Services - PartnerZone

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ADF4356 power supply rails