I haven't gone through all the specs yet, but so far I understand this =20 PIC (18F25J50) can run the RTCC in "deep-sleep" mode, and would draw =20 2uA at the highest temp of 85 deg-C. Realistically I can expect =20 <389nA at 60 deg-C or less. Specific battery no issue at this time, and yes I can fit the thicker =20 battery in there. The only issues I'll have to deal with here are that the PIC =20 interfaces to other 5V devices so I'll raise the PS voltage to =20 compensate for the diode drop, and the PIC needs a minimum of 2.35V to =20 run, so I'll probably have to use more than one battery in series. Cheers, -Neil. Quoting Robert Rolf : > What is the minimum current draw you can get on your PIC 18F* in 'RTC onl= y' > mode? > You may want to use a CR2050 (same as CR2032 but thicker, higher capacity= ). > > If the current is low enough to last for how long you need from battery, > power the RTC PIC with a diode off the power bus, and a diode > from your battery. No management chip needed. > Just be sure to have a bypass cap on the RTC PIC since the diode > makes the supply soft. > That PIC should be happy running at 4.4 volts > (diode drop) if you're not pushing the clock speed to max. > BUT you'll want to turn off the BOD since it wastes 50ua (On the > 16F parts anyaway) so use an external reset device with better specs. > > Anyone needing or knowing of a position for a PIC > hardware/software/firmware designer > in the Edmonton area, feel free to contact me privately. > > Robert > > > On Wed, Oct 2, 2013 at 8:58 PM, Neil wrote: > >> Hi all, >> >> I was happily on my way to using an MCP79412 RTCC chip to a PIC 18F >> circuit, then remembered that there are 18F's with RTCC's built in. >> But the PIC has no separate battery backup option. Main power >> (automotive 12V) to the PIC circuit *will* get cut off regularly, and >> sometimes for months, so I need to find some way to keep the clock >> running during that time. >> >> The MCP79412 would allow me to add an external battery, but if I can >> add some type of power to the PIC and use it's RTCC instead (to >> simplify and lower costs), that would be better. >> >> I could add a battery management chip, but these seem to cost more >> than the MCP79412 ($0.89ea in 100-pc qtys). >> >> Alternatively I can add a (relatively) large capacitor to the PIC, >> detect vehicle power and use a MOSFET to switch off power to the other >> components on the board (other PICs, etc). I'd probably raise the >> main regulator output voltage to 5.4-ish volts, then use separate >> diodes to the main PIC and the rest of the circuit. >> >> And I could also do something similar as the cap, but with a CR2032 or >> similar. >> >> The simplicity of the MCP79412 is nice, as I don't have to mess with >> the main PIC code for this. The battery or capacitor option would be >> nicer if it's just a dime or two in extra cost (not including the >> battery, which I'd need for any of these solutions). >> >> I'm wondering how others have tackled this. Any ideas? >> >> Cheers, >> -Neil. >> >> >> >> -- >> http://www.piclist.com/techref/piclist PIC/SX FAQ & list archive >> View/change your membership options at >> http://mailman.mit.edu/mailman/listinfo/piclist >> >> > -- > http://www.piclist.com/techref/piclist PIC/SX FAQ & list archive > View/change your membership options at > http://mailman.mit.edu/mailman/listinfo/piclist > --=20 http://www.piclist.com/techref/piclist PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist .