Re: [Gumstix-users] Overo COM input voltage

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OK - Thanks for correcting me. The chip I was referring to is the one
encircled in red I the attached image. I admit it has been a while since I
looked into this (trying to figure out if I could shutdown the HF oscillator
in any way - Realized that I couldn't :-(). AFAIR I found this chip to be a
LDO for the oscillator - Isn't this correct? Might be it is 1V8 LDO though,
meaning it would most likely have no problem going below 3V0 - I don't
remember...

To make sure we are aligned. Does this mean that the COM module can actually
run down to the TPS65950 limit of 2V7 (when it's first turned on)? Until now
I have always just the module at 3V3 since I have not been in any serious
power savings need for a product based on a Gumstix yet...

Best regards and thanks again
  Søren

---
SSC Solutions ApS - Denmark - www.ssc-solutions.dk 

> -----Original Message-----
> From: R. P. McMurphy [mailto:log...@gm...]
> Sent: Saturday, June 05, 2010 12:40 PM
> To: General mailing list for gumstix users.
> Subject: Re: [Gumstix-users] Overo COM input voltage
> 
> >> I think to remember that the VSYSTEM as well is feed through a 3V
> (or 1V8 -
> I don't remember) regulator next to TPS65950 on the board. This might
> be the
> reason why the COM module doesn't like going much lower than the 3V1
> found
> by R. P. McMurphy.
> 
> No, I think the reason is that there is a reset generator IC that
> forces reset if the input voltage is too low. Note that the Overo
> module will reliably start at, or above, 3.1V. And once started can
> run okay with the voltage down to lower than 3.0V. The reason I state
> 3.1V is that we have to be able to get the thing out of reset if the
> power is lost, and anything below ~3.1V just does nothing at start-up.
> 
> On 6/5/10, Søren Steen Christensen <li...@ss...> wrote:
> > Hi,
> >
> > I think to remember that the VSYSTEM as well is feed through a 3V (or
> 1V8 -
> > I don't remember) regulator next to TPS65950 on the board. This might
> be the
> > reason why the COM module doesn't like going much lower than the 3V1
> found
> > by R. P. McMurphy. TPS65950 can run down to 2V7 when it's first
> turned on as
> > stated previously in the snippet from the datasheet, but this of
> cause
> > doesn't help much in case the rest of the module can't :-)
> >
> > Secondly: Please keep in mind that 4V5 is absolute maximum rating for
> > TPS65950 (although it can tolerate 5V2 spikes for up to 10ms), so I
> wouldn't
> > design with supplying it from a source higher than 4V40 - 4V45 (just
> to have
> > a little margin)...
> >
> > Good luck with your project
> >   Søren
> >
> > ---
> > SSC Solutions ApS - Denmark - www.ssc-solutions.dk
> >
> >> I have had no trouble with 4.5V input. The PMIC can handle that.
> >>
> >> Voltages less than 3.0V sometimes give me trouble. Some units run
> and
> >> some don't. But 3.1V has always gives me reliable operation once the
> >> unit has started. I suspect 3.0V would probably be a safe minimum
> >> value to use to ensure reliable operation.
> >>
> >> On 5/24/10, James Adams <jam...@gm...> wrote:
> >> > Hi All,
> >> >
> >> > I would like to drive my COM module from a Li-Ion battery +
> charger
> >> IC
> >> > [Ti BQ24032] which will drive a maximum of 4.4V to the system
> (when
> >> > the AC power is present).
> >> >
> >> > The 'docs' spec the input voltage to the COM as 3.3-4.2V.
> >> >
> >> > Is there anything else on the COM module which restricts the
> voltage
> >> > range or can I drive max 4.4V, and will the unit (once turned on)
> >> keep
> >> > going down to 2V7?
> >> >
> >> > NB I know the TPS65950 won't turn on unless there is 3.2V (+/-
> 100mV)
> >> > present, the magic line from the spec says:
> >> >
> >> > "(1) 2.7 V is the minimum threshold for the battery at which the
> >> > device will turn OFF. However, the minimum voltage at which the
> >> device
> >> > will
> >> > power ON is 3.2 V ±100 mV (if PWRON does not have a switch and is
> >> > connected to VBAT) considering battery plug as the device
> >> > switch on event. If PWRON has a switch then 3.2 V is the minimum
> for
> >> > the device to turn ON."
> >> >
> >> > Thanks in advance,
> >> >
> >> > James.
> >
> >
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