[eagle] Re: SDX

Jim Sanford wb4gcs at amsat.org
Tue Feb 20 16:36:26 PST 2007


Bob:
You note is consistent with my limited memory.

Pls call after your break and when you get a chance.
73,
Jim]


Robert McGwier wrote:

>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.
>
>
>73's
>
>Bob
>N4HY
>
>
>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
>>
>>
>>
>>_______________________________________________
>>Via the Eagle mailing list courtesy of AMSAT-NA
>>Eagle at amsat.org
>>http://amsat.org/mailman/listinfo/eagle
>>
>>  
>>    
>>
>
>
>  
>
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