SuperCap HoldUp for uC
SuperCap HoldUp for uC
(OP)
I'm designing a product requiring immunity to suprise power disconnects. I need to maintain power to the circuitry to complete the sector flashing of a secure digital card write. I'll be using a LM2676 switcher @ 3.3V. Do I need to put a diode between the output of the switching regulator (coil output) and the SuperCap so when the regulator looses power, the SuperCap will not discharge into the regulator output? Will the regulator output look like a Hi-Z when it looses power and/or be damaged by the possible reverse current flow?
Any help from anyone who's done anything like this would be appreciated.
Any help from anyone who's done anything like this would be appreciated.





RE: SuperCap HoldUp for uC
http://www.national.com/pf/LM/LM2676.html
The above datasheet provides the internal diagram for the IC. The diagram seems to answer your questions.
You should also consider how to charge the supercap. I wouldn't assume that you can simply put it across the rail. Perhaps you can, but I would double check.
RE: SuperCap HoldUp for uC
RE: SuperCap HoldUp for uC
To make your life easier, why not just put the complete supercap hold-up circuit, including its charging resistor and steering diodes, after (and more-or-less separate from) the LM2676 circuit? You would have to adjust the output voltage to account for the steering diode voltage drop, or you might be able to run the voltage feedback signal around the whole thing (careful about stability).
Don't forget to signal the uC that the input power has gone out and that it should finish up what it is doing before 'nap time'. Also, keep it informed that the supercap is or isn't charged (or just a fixed delay) before it starts anything critical with the memory card.
RE: SuperCap HoldUp for uC
Thus, the current could be quite substantial, unless the output transistors are isolated in their own well. Even so, the upstream compoents might still draw current.
TTFN
RE: SuperCap HoldUp for uC
RE: SuperCap HoldUp for uC
RE: SuperCap HoldUp for uC
So, anyways, with the Aerogel caps, I'm thinking about the National TPS2111A automatic power mux. Anybody have any words of wisdom on these devices?
RE: SuperCap HoldUp for uC
RE: SuperCap HoldUp for uC
RE: SuperCap HoldUp for uC
RE: SuperCap HoldUp for uC
Anyway, this PDF has some good supercap calculation data:
http://www
Andy
RE: SuperCap HoldUp for uC
No mickey-mouse club here.
Been referencing here:
http:/
RE: SuperCap HoldUp for uC
That's a lot of stuff.
Anyway...
RE: SuperCap HoldUp for uC