Check out the Digikey catalog pages 728-729: http://dkc3.digikey.com/PDF/T041/0728.pdf http://dkc3.digikey.com/PDF/T041/0729.pdf Nick ----- Original Message ----- From: "Mike Hord" To: Sent: Sunday, February 08, 2004 4:13 PM Subject: [PICLIST] [EE:] Post battery pull runtime > I'm working on a battery operated system that I would like > to shut down gracefully when someone yanks its battery. > > I'm using a TPS6021x charge pump regulator from TI, which > has a low battery indicator to notify the system if the power > ever falls below ~1.18V, which of course will be the case if > the battery is pulled. What I'd like to do is hook up the LBI > output to the INTx pin, so upon power failure, the PIC (in > this case, an LF2320) will wake up and immediately start into > the needed preparations for power loss. > > I'd really like it if the PIC were able to log the time the power > failed and set a flag in its internal EEPROM, and issue a write > buffer command to the external DataFlash where it stores the > data it collects. My problem is simply one of providing power > to the system long enough for it to do these things. > > The DataFlash requires 14 mS max and 35 mA max to write > from buffer to flash page. If I throw in 1 mA to cover the > PIC, which seems reasonable per the datasheet, my > i=C dV/dT calculation is indicating over 1300 uF to keep the > 3.3V system voltage above the 2.7V the DataFlash needs to > operate long enough for the write to proceed. That's a > fairly unreasonably large capacitor for this circuit. > > So, my question is this: what other spiffy little tricks are there > to give just enough juice to shutdown gracefully? I'm thinking > about using a 3V lithium button cell that I can switch into the > circuit using an NMOSFET between its negative pole and the > system ground. Good idea, bad idea, indifferent? > > Mike H. > > _________________________________________________________________ > Check out the great features of the new MSN 9 Dial-up, with the MSN Dial-up > Accelerator. http://click.atdmt.com/AVE/go/onm00200361ave/direct/01/ > > -- > http://www.piclist.com hint: The PICList is archived three different > ways. See http://www.piclist.com/#archives for details. > -- http://www.piclist.com hint: The PICList is archived three different ways. See http://www.piclist.com/#archives for details.