[time-nuts] Power Supply for AD9852 / AD9854

Jim Lux jimlux at earthlink.net
Sun Mar 16 12:08:54 EDT 2014

On 3/16/14 8:13 AM, d0ct0r wrote:
> Thanks ! Looks like I am on the right track.
> I've attached couple of documents which could be useful. I'am going to
> use two separated voltage regulators for VCC/AVDD and DVDD. And use 10
> Ohm / 100Mhz  ferrite board and few capacitors to "separate" VCC and AVDD.

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."

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