STM32 Crystal Load Capacitance Calculator
Use this calculator to determine the optimal capacitor values for your STM32 microcontroller's crystal oscillator circuit, ensuring frequency stability and reliable startup.
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.
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