FC3215AN32.768K-90NN60KC3 is a low-ESR, compact 32.768 kHz crystal unit designed for sub-clock applications in battery-powered and IoT devices. The device features a robust Pb-free metal lid with seam-sealed package and operates across a wide temperature range of -40°C to +105°C, with typical ESR of 35 kO at +25°C and maximum ESR of 60 kO across the full operating range. It achieves a frequency tolerance of ±20 × 10?6 at +25°C ± 3°C and incorporates a newly redesigned tuning-fork crystal element based on decades of in-house design and production expertise. The unit is ideal for wireless modules, wearable products, low-power microcontrollers, and battery-powered IoT applications requiring minimal current consumption and reliable long-term performance.