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)
[email protected] 
---------------------------


-----Original Message-----
From: Howard Long [mailto:[email protected]] 
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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