[eagle] Re: SDX

Robert McGwier rwmcgwier at gmail.com
Tue Feb 20 14:53:45 PST 2007

I do not think this is right.  I believe we discussed the ACP experiment 
and believe that we need heat sink module to handle the FPGA's heat 
engines in it.

Lyle and I have not discussed the FPGA in the SDX experiment which will 
be used to generator the polar representation of the baseband signal and 
some other processing to be passed out to the HELAPS drivers, amplifiers 
and modulators.  I do not believe we have a heat budget yet for that 
part at full speed but I am expecting it to not be high.

The ACP will have two FPGA's in it probably, one for TX and one for RX.  
These processors will be 10w total in our best guesstimate at the 
current state of technology.  The ACP does not have a design yet.

The TI part should not be toasty and the RAM will not be toasty.  I 
think this note is wrong given my current understanding of the 
technologies involved.  If I said SDX,  I was not being careful.

I have been on the road and away from home for many days except for two 
periods under 24 hours.  I have not been returning many phone calls and 
emails and I apologize.  I will return home on Thursday at which time I 
am informed by my boss (N2HPE) that I need a long break.  ;-)  My 
apologies to one and all.



Dick Jansson-rr wrote:
> Howard:
> Some time ago, Bob McGwier and I discussed the SDX thermal issue and pretty
> well decided that this module would need to be one of our heat sink module
> designs, either E05 25 or if you need it larger the E05 15 module. These
> will be specially treated in their mounting in the spacecraft and not be
> thermally isolated from the spaceframe as the other, non-power modules are
> handled. In this module the power devices are clamped directly to the heat
> sink using a space-rated thermal compound at their interfaces. The
> interfacing of devices such as the PowerPAD from TI, will need some study of
> the papers that you have referenced. That will not obviate the treatment of
> the module as a power device, however. I shall be back to you on this. In
> the meantime, please take the time to study the drawings on these modules so
> that you become familiar with this design.
> Dick Jansson, KD1K
> (ex: WD4FAB)
> kd1k at amsat.org 
> ---------------------------
> -----Original Message-----
> From: Howard Long [mailto:eagle at howardlong.com] 
> Sent: Tuesday, 20 February, 2007 1117
> To: 'Dick Jansson-rr'; 'AMSAT Eagle '
> Subject: RE: [eagle] URx
> Hi Dick, John,
>> Device       Dissipation     Delivered 
>> U16           0.340             0.850
>> U17           0.411
>> U18           0.384             1.200
>> U19           0.108             0.090
>> U20           0.040             0.224
>>                 ------------        ------------
>> Totals       1.283W          2.364W
>> For a grand total power dissipation of the power system of 3.647W.
> I am particularly interested in this as the DSP device on the SDX
> (TMS320C6726) typically dissipates 857mW at its full 250MHz speed. It is a
> 144 pin LQFP PowerPad device and has a metal plate directly underneath the
> die that is designed to be soldered directly to the PCB ground plane.
> In order to conduct heat away, TI recommend the optimum to be 100 0.33mm
> vias in a 10x10 matrix.
> See http://www.g6lvb.com/dspthermal.jpg for the design I developed for the
> prototype I use for my software development.
> We will almost certainly need to conduct heat away from the device on the
> underside, so that would suggest to me a direct metallic interface between
> the board and the module housing, either milled out of the chassis itself or
> with an interfacing block. IT should be noted that for electrical reasons
> there are also 44 decupling capacitors on the bottom of the PCB that need to
> be considered when providing the thermal interface.
> We also would need some space rated goo to ensure good thermal conductivity
> between the PCB and the heatsink - I am sure someone will know what this is!
> One final thing - 3.647W seems very high for the receiver function. Is this
> based on real figures or device spec sheets, and if the latter are these
> worst case or typical values?
> 73, Howard G6LVB
> PowerPADT Thermally Enhanced Package
> http://focus.ti.com/lit/an/slma002a/slma002a.pdf
> PowerPADT Layout Guidelines http://focus.ti.com/lit/an/sloa120/sloa120.pdf
> PowerPADT Made Easy http://www-s.ti.com/sc/psheets/slma004b/slma004b.pdf
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AMSAT Director and VP Engineering. Member: ARRL, AMSAT-DL,
"Taking fun as simply fun and earnestness in earnest shows
how thoroughly thou none of the two discernest." - Piet Hine

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