[time-nuts] Power Supply for AD9852 / AD9854

[EWKehren at aol.com]

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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