NicheCalcs

What this calculator is doing

This calculator computes the appropriate values for the two load capacitors \( C_1 \) and \( C_2 \) connected to the crystal oscillator of an STM32 microcontroller. The calculation uses the crystal's specified load capacitance (\( C_L \)) and accounts for stray capacitance (\( C_{stray} \)) on the PCB and MCU pins. The load capacitance formula is: \[ C_L = \frac{C_1 \times C_2}{C_1 + C_2} + C_{stray} \] Assuming \( C_1 = C_2 \), we solve for \( C_1 \) and \( C_2 \): \[ C_1 = C_2 = 2 \times (C_L - C_{stray}) \] Where: - \( C_L \): The load capacitance specified in the crystal datasheet (typically 12 - 20 pF). - \( C_{stray} \): Parasitic capacitance from the PCB traces and MCU pins (typically 3 - 7 pF). This calculation ensures the crystal oscillates at the correct frequency and with stable startup conditions.