Every designer wants his products to be smaller and use less power. If the RTC can be made to consume less power, then the backup battery can be made smaller or provide more backup time. The unfortunate side effect is that the RTC’s power consumption cannot be reduced without also reducing its crystal drive capability. The standard 32KHz crystal used in conjunction with the RTC oscillator has the characteristic that as the crystal gets smaller, it demands more drive current. The equivalent series resistance (or ESR) increases as the crystal gets smaller.  Small surface mount crystals were not envisioned when the original Real-Time clock oscillator was designed. Therefore, many of the Real-Time clocks on the market do not have sufficient drive current available to work with the smallest or high ESR crystals. These two trends force the designer to choose between saving space by using the smallest high ESR crystals that require more power and a larger backup source or using a lower power RTC that needs a large and low ESR crystal. Additionally, if the RTC could be designed such that timekeeping data can be maintained at a lower voltage than possible with what the market currently offers, the design could use fewer or smaller backup batteries, reducing system cost, size, and weight. Finally, it would be desirable if the customer could use a single RTC in different designs that call for different crystals, simplifying BOMs and reducing the number of components that would need to be qualified.