Intermediate 12 min read

MLCC Capacitor Selection Guide

Learn how to select the right MLCC capacitor for your application.

Introduction

Multi-layer ceramic capacitors (MLCCs) are the most widely used capacitors in electronics. Selecting the right one requires understanding dielectric types, voltage derating, and DC bias effects. This guide walks you through the key considerations.

Dielectric Types

MLCCs are classified by their dielectric material, which determines temperature stability and capacitance change:

  • C0G (NP0) — Ultra-stable. Capacitance changes less than ±30ppm/°C. Ideal for timing circuits, oscillators, and filters.
  • X7R — Stable across −55°C to +125°C with ±15% tolerance. Good general-purpose choice for decoupling.
  • X5R — Stable across −55°C to +85°C with ±15% tolerance. Higher capacitance density than X7R.
  • Y5V — Wide tolerance (+22% to −82%). Very high capacitance density but poor stability. Avoid for critical circuits.

Voltage Derating

Always derate the voltage rating of ceramic capacitors. A good rule of thumb is to use no more than 50–70% of the rated voltage. For a 3.3V rail, use a capacitor rated for at least 5V, preferably 10V.

MLCCs can lose significant capacitance under DC bias. A 10µF 10V X5R capacitor may only provide 3–4µF at 5V DC bias. Check the DC bias curves in the manufacturer datasheet.

Selecting Values for Decoupling

For digital IC decoupling, use this approach:

  • Bulk decoupling: 10µF X5R or X7R near the power entry point.
  • Local decoupling: 100nF X7R close to each IC power pin.
  • High-speed ICs: Add 10nF or 1nF C0G in parallel with 100nF for broadband decoupling.

Package Size Considerations

Larger packages generally offer better voltage ratings and lower ESR. For 100nF decoupling, 0402 is sufficient for most designs. For 10µF and above, 0805 or 1206 packages are typically required to achieve reasonable voltage ratings.

Common Pitfalls

  • Using Y5V for timing-critical circuits — the capacitance varies too much with temperature and voltage.
  • Not accounting for DC bias derating — the actual capacitance may be much lower than the nominal value.
  • Mixing dielectric types in parallel without considering their different temperature coefficients.

Conclusion

For most designs, X7R in 0603 or 0402 is a safe default for decoupling. Use C0G for precision analog circuits. Always check the manufacturer's DC bias and temperature curves, and derate voltage by at least 30%.