The FC3215AN32.768K-90NN60KC0 is a low-ESR 32.768 kHz crystal unit designed for sub-clock applications in battery-powered and IoT devices. It features a compact 3.2 × 1.5 mm package with a maximum thickness of 0.9 mm, and delivers typical ESR of 35 kO at +25°C with maximum ESR of 50 kO across -40°C to +85°C and 60 kO across -40°C to +105°C. The device maintains a frequency tolerance of ±20 × 10?6 at +25°C ± 3°C and supports an extended operating temperature range from -40°C to +105°C, making it ideal for wearable products, wireless modules, and low-power microcontroller applications. Its Pb-free metal lid with seam-sealed package and tuning-fork crystal element design ensure robust performance and low current consumption for extended battery life in demanding environments.