In summary, most RTCs on the market are not capable of reliably oscillating with 32kHz XTALs with an ESR higher than 50kΩ. The obvious trend for portable equipment is smaller size and lower power. A smaller XTAL tends to have a higher ESR. However, the higher the ESR, the higher the power consumption by the oscillator will be. To address this market need, Analog Devices has introduced a line of serial RTCs with SPI and I²C interfaces that support 6pF and 12pF 32kHz XTALs with ESR up to 100 kΩ with an oscillator current less than competitive solutions with lower ESR compatibility.