The DSC6021JI2B-01STT: For a battery-powered IoT node that spends 99% of its time in sleep, the oscillator's own consumption stays below the MCU's RTC current, so it does not dominate the sleep budget.
Package and board integration
The CMOS output swings rail-to-rail into a standard 15 pF load, so no external termination resistor is needed at the oscillator pin — the trace impedance to the first clock load should be kept under 10 mm to avoid reflections at the 12 MHz edge rate.
