Hi Michael, Actually I believe it was supposed to be a Schottky diode (note the shape of the bar with those tiny protrusions). What would be the concern wiht the diode drop -- there is about 0.3V voltage drop across the diode when the mote is connected to USB (under that scenario, we're not necessarily trying to operate in the most power efficient mode) and the mote still gets a very stable supply of about 3V. When the mote is disconnected from USB, the diode prevents the current to flow into the USB side of circuitry, and so any voltage drop across the diode is not an issue.
Cheers, Rob On 9/27/07, Michael Schippling <[EMAIL PROTECTED]> wrote: > You have any idea why that diode is (or appears to be) a Zener? > And there's a diode-drop issue, isn't there? > > Just idle curiosity... > MS > > > Robert Szewczyk wrote: > > Michael is correct here: the power from the USB connector U4 (about > > 5V) goes through a U25 which is a voltage regulator that produces > > 3.3V. That voltage goes through the diode so that the USB side of the > > mote is not reverse-powered when the mote runs on batteries and the > > mote is disconnected from USB. > > > > Cheers, > > > > Rob > > > > On 9/27/07, Michael Schippling <[EMAIL PROTECTED]> wrote: > >> Boy, that's a tough one...I'm not entirely sure without looking up all > >> the chips but I think when powered by the USB it goes sorta like this: > >> > >> page 3 top-left "USB Interface" > >> U22 pin 4 -- power from host -- becomes U_VCC > >> U25 TC55RP33 -- does some magic to make -- P_DVCC > >> > >> page 3 top-right "Mote Power" > >> P_DVCC -- goes through D22 to become -- VCCin > >> (I'm not clear on the use of a Zener here, if that is what it is...) > >> > >> page 1 top-right "Power" > >> VCCin -- goes through L2 to become -- DVCC > >> > >> But, if as you say, ( PWR_CONN) U4 pin 1 - VCCin - does not connect > >> to D22 pin2 - VCCin - then all bets are off. Make sure you got the > >> right pin of the diode when doing the continuity check, or the > >> right polarity if checking through the diode... > >> > >> MS > >> > >> xi zhang wrote: > >>> Hi all, > >>> I'm trying to profile the power consumption of the TelosB mote when > >>> powered from USB. I've looked at the schematics of TelosB but I could > >>> not figure out how the DVcc is generated when powered through the USB. > >>> In addition, I would also like to know where is the Vccin (which is fed > >>> to diode D22) generated since a short circuit test has shown that it is > >>> not from power supply U4. > >>> > >>> Thank you very much! > >>> > >>> Best Regarts, > >>> Xi Zhang > >>> > >>> > >>> ------------------------------------------------------------------------ > >>> > >>> _______________________________________________ > >>> Tinyos-help mailing list > >>> [email protected] > >>> https://www.millennium.berkeley.edu/cgi-bin/mailman/listinfo/tinyos-help > >> _______________________________________________ > >> Tinyos-help mailing list > >> [email protected] > >> https://www.millennium.berkeley.edu/cgi-bin/mailman/listinfo/tinyos-help > >> > _______________________________________________ Tinyos-help mailing list [email protected] https://www.millennium.berkeley.edu/cgi-bin/mailman/listinfo/tinyos-help
