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Date Posted: 19:53:09 03/10/02 Sun
Author: Chris
Subject: Alchemy vs. Gazelle boards: 3.3V supply thoughts

Just some thinking out loud that I realised might generate useful results on this forum...

Fact: Alchemy boards require a 3.3V supply in all configurations.
Fact: Gazelle boards, in their stock configuration (RAM, no PCI cards, no cache), do NOT require a 3.3V supply.
Fact: The power supplies from the 6360, 64/6500, and 54/5500 can be used to power any Gazelle or Alchemy board.

Someone else's speculation: the Gazelle boards have an onboard 3.3V regulator that supplies the necessary voltage at minimal current draw.
Another speculation: PCI (or L2 cache) cards that draw lots of 3.3V power will cause the installation to fail unless a 3.3V supply is present.

Something I may or may not be remembering properly: people have had to add the 3.3V supply even without cards that draw lots of 3.3V current.

My speculation, based on all of the above: the Gazelle boards use the incoming +5V line to generate the 3.3V supply for the board. This line does *not* get high priority, however, so if devices that use a lot of 5V current are present, the board doesn't get enough +5V to run its onboard regulator.

Further speculation, based on the above: It won't make Alchemy boards work, but adding sufficient 5V power to a Gazelle installation *should* obviate the need for a 3.3V supply in most cases. (Are there any cards that have a high 3.3V current draw? If so, what are they?)

Can anyone confirm or disprove this? It sure would clear up a lot, at least in my mind...

cl

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Replies:

Re: Alchemy vs. Gazelle boards: 3.3V supply thoughts -- Derek Sweeney, 16:09:26 03/13/02 Wed
- Re: Alchemy vs. Gazelle boards: 3.3V supply thoughts -- Chris, 17:13:14 03/13/02 Wed