|Linear Technology's LTC6991 is a silicon oscillator with a programmable period range of 1.024ms to 9.54 hours (29.1μHz to 977Hz) that is specifically intended for long duration timing events. The LTC6991 is part of the TimerBlox™ family of versatile silicon timing devices.
A single resistor, RSET, programs the LTC6991’s internal master oscillator frequency. The output clock period is determined by this master oscillator and an internal frequency divider, NDIV, programmable to eight settings from 1 to 2²¹. Datasheet