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Laundry list of questions from Firefly

Question asked by stevereine Employee on Nov 3, 2015
Latest reply on Nov 4, 2015 by tlili

Hi Folks,


I've got a list of questions from Firefly on the AD9361, can you help out?





  1. 1.    How is power divided on the 1.3V supplies in the AD9361 reference design?  My design has two AD9361 parts onboard, and I am trying to figure out whether this requires 4 of the ADP1755 LDOs, or whether that number can be reduced. I also want to estimate the current from the LDOs for thermal analysis.


  1. 2.    All of the current numbers in the AD9361 datasheet are listed as typical.  Is there a recommended multiplier for using the part at worst case PVT?  I would like to ensure that I’ve sized all of my switching supplies appropriately.  Since I’m guardbanding this anyway, I don’t need an exact value, but I’m assuming something like 1.8A per part worst case on the 1.8V rail (primarily through the LDOs to 1.3V) at the moment.  Is this assumption reasonable?


  1. 3.    The datasheet calls for an RC snubber (1uF, 1 ohm) on TX_VCO_LDO_OUT and RX_VCO_LDO_OUT, but doesn’t give an estimated power dissipation.  I’d like to use an 0402 resistor, is this reasonable?


  1. 4.    Is port 0 of a AD9361 capable of both single-port FDD and TDD modes?  Alternatively, I may ask about how to gang ANT1 and ANT2 on the BSC9131 together, but that’s a Freescale question.


  1. 5.    For the AD9361, are the differential outputs 100 ohm?  This matters both from my distance to the balun (currently) or if we use something like the twinax you showed me yesterday.


  1. 6.    For the ADP1755 with 1.8V input, 1.3V output, can I pull the PG pin to 3.3V?  This seems to be allowed by the absolute rating on the part, but the datasheet says it “requires an external pull-up resistor to VIN” (pg 12).


  1. 7.    For the ADP5054, the datasheet has a section on “Input Capacitor Selection” (pg 22) which has a calculation for the RMS current rating of the capacitor. Does ADI have any guidance on an appropriate value for the input capacitor on each channel?