Using a supercapacitor to provide power outage monitoring capability to a micro circuit.

I am using a MSP430 micro and its superior low current modes in an AC powered application that needs to know that AC power has been lost for more than 20 minutes.  I'm thinking that a supercapacitor is the way to go and that all I need is a clever IC that can charge the cap, regulating the output in some way.  Avoiding extra diode drops and such and integrating in the regulation so that a separate requlator isn't needed would seem to be good things to look for.  So far I've found an IC made by Linear, ie LTC3225 which comes close.  Being able to run the supercap charger from a wider voltage range would be a bonus.  Does TI have any ideas?   I'd be relying on the MSP430's wide supply range (1.8V to 3.6V).  I.e. charge the supercap to 3.6V, when power goes down, enter low power mode, periodically waking up to see where time and charge are at, and with a careful design I'd probably have a few hours before hiting the 2.7V not allowed to write to flash limit.