Hey all,
I have a couple of questions for power switches which I believe Tim and I
kind of touched on last meeting, but I'm still a little unclear about.

The controller chips allow youto set a limit to the power dissipated in the
N-channel FET, and also provides a couple equations to use in calculating
this power limit.  Tim, as we were calculating last meeting, the power
dissipated under "normal" operating conditions is only about 0.17W, based on
an Rds_on calculated to 6.75 mOhm, max current of 5A, and max junction temp
of around 115C.  However the equations provided to calculate power limit
take into consideration max desired ambient, junction, and case temperatures
whose values I am unsure of.  In the old APS design notes, power limit to
the FETs is set to 1/3 W which seems reasonable enough to my inexperienced
mind, but may be wrong now that there are 8 switches instead of 4.  Does
anyone have any suggestions, or ideas as to a reasonable power limit?

I think I need a little clarification as to which chips need to be selected
by tomorrow.  My assumption is that all the chips we will need for the
remainder of the project should be chosen, however this being the first time
I've really done any chip shopping, finding the power switch chips has
pretty much been my focus thus far.  I think that finding the ideal diode
thing for the umbilical should be pretty easy based on the relative
simplicity of that particular circuit, but as for the pyro switches and
igniters, I haven't had a chance to search at all.  Should I be hustling to
get these chosen as well at this point?

On Thu, Feb 19, 2009 at 2:53 AM, Andrew Greenberg <and...@psas.pdx.edu>wrote:

> AiLing:
>
> I don't remember if I told you or not: Sarah officially approves of the
> USB2507 hub chip. I'm still waiting to hear if we're going to get the
> $300 evaluation board donated or not: I'd hate to pay $300 for a hub chip!
>
> The samples of the Honeywell ASDX015A24R-DO pressure sensors have been
> ordered... hopefully they'll arrive early next week.
>
> Jeremy and Mike:
>
> The ASDX015A24R-DO uses I2C. Please add that to your requirements.
>
> Daniel:
>
> Any word on getting some of Keithp and Bdale's sensor?
>
> Andrew
>
> --
> -------------------------------------------------------
> Andrew Greenberg
>
> Portland State Aerospace Society (http://psas.pdx.edu/)
> and...@psas.pdx.edu  P: 503.788.1343  C: 503.708.7711
> -------------------------------------------------------
>
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