How to select the smd capacitor in the circuit

    The SMD capacitor in the three major SMD electronic component are mainly used for filter coupling on the circuit board. For the selection of SMD capacitor, the following characteristics should be paid attention to: capacity, withstand voltage, temperature range, component packaging form and size; Ripple current, ripple voltage; leakage current, ESR, dissipation factor, impedance/frequency characteristics; capacitor life; comprehensive considerations such as actual needs, performance and cost.

    For temperature-sensitive electronic products: First consider NPO materials. NPO is the most commonly used MLCC with temperature compensation characteristics. Its filling medium is composed of rubidium, samarium and some other rare oxides.

    C0G has the most stable capacitance and dielectric loss, and the widest operating temperature range. When the temperature is from -55°C to +125°C, the capacity change is 0±30ppm/°C, and the change in capacitance with frequency is less than ±0.3ΔC. The drift or hysteresis of the C0G capacitor is less than ±0.05%, which is negligible relative to the film capacitor greater than ±2%. The variation of its typical capacity relative to the service life is less than ±0.1%.

    For cost-sensitive electronic products: X7R material is preferred. X7R capacitor are called temperature stable ceramic capacitor. The temperature characteristic of X7R capacitor is inferior to C0G. When the temperature is between -55℃ and +125℃, its capacity change is 15%. It should be noted that the change of capacitor capacity is nonlinear at this time. The capacity of X7R capacitor is also different under different voltage and frequency conditions. It changes with time, about 1% ΔC every 10 years, which is about 5% change in 10 years.