[eagle] Re: SDX

Dick Jansson-rr rjansson at cfl.rr.com
Tue Feb 20 16:09:05 PST 2007


Bob:

Thank you for clarifying my fuzzy brain. I mistook Howard's work for the
ACP.

Dick Jansson, KD1K
(ex: WD4FAB)
kd1k at amsat.org 
---------------------------


-----Original Message-----
From: Robert McGwier [mailto:rwmcgwier at gmail.com] 
Sent: Tuesday, 20 February, 2007 2254
To: Dick Jansson-rr
Cc: 'Howard Long'; 'AMSAT Eagle '
Subject: Re: [eagle] SDX


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
>
>   


-- 
AMSAT Director and VP Engineering. Member: ARRL, AMSAT-DL, TAPR, Packrats,
NJQRP, QRP ARCI, QCWA, FRC. ARRL SDR WG Chair "Taking fun as simply fun and
earnestness in earnest shows how thoroughly thou none of the two
discernest." - Piet Hine





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