[hpsdr] Hot ADC

[Philip Covington]

On Tue, Jan 13, 2009 at 1:53 PM, Kjell Karlsen <la2ni at online.no> wrote:
> ***** High Performance Software Defined Radio Discussion List *****
>
> I do not have a thermometer to measure the temp of the ADC but it felt very
> hot, much more than I liked. I glued a small Heatsink on top of the chip and
> it helped a bit. When I had a look at the  aeria on the bottom of the board
> directly under the chip, I discowered that the solder may not have melted
> properly when the board was produced. There was no sign of solder up in the
> holes below the ADC. I resoldered the aeria and now the bottom of the card
> is warmer than before. Unfortunately I can not confirm this by measurements,
> but my feeling is that the chip is colder now.
>
> Can someone do a tempereture measure before and after resoldering and report
> back?
>
> Kjell

I have measured the LTC2208 ADC temperature of quite a few QS1R
receiver boards (this is done as part of the manufacturing tests).  If
the ADC is soldered properly, the average temperature on the top
surface of the ADC is around 54 C ( 130F ).  If it is considerably
higher than that it is usually because of inadequate soldering of the
thermal pad on the underside of the ADC.

I don't know how the thermal pad is designed on the Mercury, but 70 C
( 158F) is excessive, I'd think.

Gluing a heatsink to the top of the ADC does not help much.  The heat
removal should be via the thermal pad through the PCB.

-- 
Phil Covington
Software Radio Laboratory LLC
Columbus, Ohio
http://www.srl-llc.com
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