[time-nuts] Power Supply for AD9852 / AD9854 correction

EWKehren at aol.com EWKehren at aol.com
Sun Mar 16 16:43:00 EDT 2014


Correction I did put pin 4 on the same regulator as the PIC. Had to have  
one for the PIC so why not use it. Do not know if it made a difference.
Bert
 
 
In a message dated 3/16/2014 3:58:20 P.M. Eastern Daylight Time,  
EWKehren at aol.com writes:

You have  not said any thing as to what you expect to get out  of the DDS 
and  how important certain parameters are. We recently did a AD 9913  that 
Tom  
tested extensively  http://www.leapsecond.com/pages/ad9913/ using  a  
single 
supply for the DDS. Some may take exception but it works  for us. The AD  
9913 is nice for time nuts applications since it  allows precise offsets 
and we  
use it in applications like Dual Mixer  and what I call the Austron 
circuit, 
a  circuit that is a single  channel digital mixer with ping pong counter 
and  yields 1 E-12 in 1  second. Not ready for release yet.
AD 9913 board is attached.
Bert  Kehren



In a message dated 3/16/2014 12:36:48 P.M. Eastern  Daylight Time,  
time at patoka.org writes:



I would assume  that using two voltage regulators will  spread the load. 
For the  AD9851 I'am planning to put external radiator  glued on top of  
it.

Regards,

V.P.

> those parts  dissipate a  fair amount of heat, and they're not very big.
> If you turn  on  everything in the 9854 AND run it at 300 MHz clock, it
> draws  about  1.2 Amps (@ 3.3V) which is about 4 Watts.. that's a lot of
>  power to  get out of the part and keep Tj reasonable. Board layout  to
> get the  heat out is very important.  If they get too  hot, they start
> to  act flaky.  You get extra spurs and more  importantly, they don't
>  respond to the programming properly  (e.g. you send the serial stream
>  to program frequency X, and  instead it programs some different
>  frequency).
> 
>  
> "The heat sink of the AD9854ASVZ 80-lead  TQFP package  must
> be soldered to the PCB. "
> 
> "Adequate   dissipation of heat from the AD9854 relies on all
> power and  ground  pins of the device being soldered directly to
> a copper  plane on a PCB.  In addition, the thermally enhanced
> package of  the AD9854ASVZ has an  exposed paddle on the
> bottom of the  package that must be soldered to a  large copper
> plane, which,  for convenience, can be the ground  plane."
--   
WBW,

V.P.
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