Re: [Gumstix-users] How To Power A Stack-O'Stix?

[Stephen H. <n1...@rc...>]

Thanks, Don.

So, if I understand the Wiki correctly, the following statements are true:

1) In this stack, I should power the Robostix, (with at least 6V to accommodate voltage regulator headroom), and not power the NetMMC card. 

2) Having multiple MIC5219 regulator chips (on different daughterboards) connected to the 3.3V rail, with only one of them powered, is not a cause for concern.

3) If I put an SD card in the MMC/SD socket, the power consumption of the NetMMC board may exceed the 500 ma rating of the Robostix 3.3V regulator, requiring some additional measures to power the system (such as powering the NetMMC as well, or using a higher-rated voltage regulator for the 3.3V rail  in place of the Robostix' MIC5219).

Again, thanks!

Regards, Steve 

---- Original message ----
>Date: Tue, 27 May 2008 10:01:08 -0700
>From: "Don Anderson" <do...@gu...>  
>Subject: Re: [Gumstix-users] How To Power A Stack-O'Stix?  
>To: n1...@ar...,"General mailing list for gumstix users." <gum...@li...>
>
>   Stephen
>
>   Thanks for the reminder re constantly improving the
>   documentation.
>
>   Perhaps some of the FAQs posted here will answer
>   your questions located on the docwiki:
>
>   http://docwiki.gumstix.org/index.php/Frequently_asked_questions/Heat_and_power#Can_just_one_power_supply_be_used_for_two_or_three_board_configurations.3F
>
>   Don
>   +++++++++++++
>
>   On Tue, May 27, 2008 at 9:49 AM, Stephen Hersey
>   <n1...@rc...> wrote:
>
>     OK, color me annoyed.
>     I've purchased a Connex motherboard and Robostix
>     and NetMMC expansion modules, and I want to make
>     sure not to fry'em when I power them up. Sooo,
>     I've been scouring the Web site, the newsgroup
>     archives, and the schematics. Alas, while Gumstix
>     circuit design is cool and creative, their
>     documentation is sadly deficient.
>
>     Trouble is, I cannot find any information telling
>     me how to power the aforementioned stack properly.
>     Both the Robostix and NetMMC have DC input jacks;
>     presumably, the processor is powered from the
>     voltage regulator on an expansion card.
>
>     Now, I can see two possible ways to power this
>     stack, and there's NO CLUE ANYWHERE on the Gumstix
>     site telling me how to determine the proper power
>     system for a multiboard stack. Options seem to be:
>
>     A) Supply 5V power to the Robostix alone (since
>     the ATMEGA128 is a 5V chip), and hope that its
>     regulator can handle the 3.3V bus load from all
>     three boards; this seems chancy, as I read
>     somewhere that the NetMMC should get 4V instead of
>     5V, presumably to limit the power dissipation on
>     the 3.3V regulator; consequently, the Robostix
>     3.3V reg will take a thermal hammering from this
>     treatment and may cook.
>
>     B) Supply 5V to the Robostix, and 4V to the
>     NetMMC; also chancy, as it's generally a Bad Idea
>     to connect the outputs of two independent voltage
>     regulators, which would appear to be the probable
>     result of doing this; the Micrel datasheet for the
>     MIC5219 regulator doesn't suggest this as a
>     potential option, either.
>
>     C) Perform surgery on the boards to disconnect
>     their internal regulators, and provide external
>     3.3V and 5V power; this is  unappealing, since
>     these boards are supposed to work together without
>     microsurgery.
>
>     Can anyone provide a rational approach to powering
>     this stack?
>     Is there a document somewhere on powering a stack
>     that I've overlooked?
>
>     Thanks, Steve H
>                                                      
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Each of us has strengths and talents that others don't. Whether innate or learned, these are gifts -- and a gift not shared is a sad and lonely thing. Using our gifts for the benefit of all is an ethical obligation for every intelligent being. (The magic only works if you pass it on!)