Hi Dave, quick confirmation on what you recommended:
I can plug anywhere from +5 to ~+9 into the V-Board connector on the
robostix, powering that board? Then I'll can just have my regular 7805
delivering +5.00V to the CFstix/Gumstix combination?
9V ---> |robostix|=3Dhirose=3D|gumstix/cfstix| <---5V
On 4/24/06, Dave Hylands <dhylands@...> wrote:
> Hi Eric,
> > Quick little problem to deal with here: does anyone have some
> > recommendations on a simple circuit to supply 5V to a gumstix/robostix
> > stack?
> > Currently I'm using a 7805 regulator with some caps and a fuse
> connected to
> > a +9V battery in. It supplies the correct voltage, ~+5.044V, when the
> > gumstix isn't plugged in, but when it is plugged in, the voltage drops
> > +4.7V and starts causing segmentation faults on the robostix when I run
> > i2c-io. So I tried ramping the input voltage up to +12V, since the
> > regulator should be able to take this, but the 7805 gets extremely hot
> in a
> > very short time. I checked the current when it's running, and the
> > gumstix/robostix stack (and a wifi cf card) seems to draw ~450mA, way
> > much for this circuit.
> > What are you guys using? Anyone have some some suggestions for
> > else than a 7805, which seems like it can't supply enough current? Any
> > would be greatly appreciated...
> The robostix has onboard regulators already. +12 is a bit on the high
> side, but +9 should be OK.
> 5v is too low (since the voltage regulators which are on the board try
> to output 5v but need a bit more for headroom.
> In particular, the MIC5219 regulator on the board can drop as much as
> 600mV depending on the amount of load. So you need 5.6v or higher.
> There are a total of four voltage regulators on the robostix. One of
> them is dedicated for the gumstix. However its only rated at 500 mA,
> so if your CF card will draw 450mA then that's too much.
> What you can do is to take the input to your 7805 and connect it to
> the robostix power and take the output of your 7805 and connect it to
> the power on the cfstix. This way you'll get 500mA from the robostix
> power supply, and whatever your 7805 is rated at from it.
> You want your input to the 7805 to be a minimum of 7.2v (so it has
> 2200mV dropout), but as close to 7.2v as you can. Perhaps 7 1.2v
> batteries for a nominal 8.4v.
> Better yet, use a low-dropout regulator like the LM2940 which has a
> 500mV dropout voltage, and is available in the same package as the
> 7805. Then you could use 6 1.2v NiMH or NiCAD batteries.
> Dave Hylands
> Vancouver, BC, Canada
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