[time-nuts] Power Supply for AD9852 / AD9854

Bob Camp lists at rtty.us
Sun Mar 16 13:18:19 EDT 2014


If you use multiple regulators for the same supply and they don’t come up at the same time, odd things can happen. On some chips those odd things include smoke. In most cases where it fails, the more common effect is the internal reset does not work properly and you can’t talk to the chip. 

You really need a multi layer board to heat spread these chips, you also need to reflow solder them to get the bottom pad properly connected to the via’s under the chip. Unless it’s already on a board, this is not a simple chip to use in a home environment. 


On Mar 16, 2014, at 12:34 PM, d0ct0r <time at patoka.org> wrote:

> 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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