Why Must MLCCs Be Derated

1. What Is MLCC Derating?

Derating means:

Operating the capacitor at a voltage significantly lower than its rated voltage — typically 50% or less.

Example:

The circuit runs at 5V. Instead of choosing a 6.3V MLCC, you select a 16V or 25V part.

This is not "over-engineering" — it's necessary to ensure effective capacitance.

2. Why Derate? — The Core Reason: DC Bias Effect

What Is the DC Bias Effect?

For Class 2 ceramic capacitors (X7R, X5R, Y5V, etc.), applying a DC voltage causes the effective capacitance to drop significantly.

This is a physical property of the ceramic material, not a quality defect.

How Severe Is It?

Rated Voltage	Actual Working Voltage	Remaining Effective Capacitance (Typical)
10V	10V	30% ~ 50%
10V	5V	60% ~ 80%
10V	3.3V	80% ~ 90%
16V	5V	85% ~ 95%

Real-World Example

A 10V / 10µF X7R MLCC may only provide 6µF at 5V, and only 3~4µF at 10V.

Using a 25V-rated capacitor of the same capacitance, at 5V you can retain over 9µF.

3. Core Principles of MLCC Derating

Application Scenario	Recommended Derating Ratio
Power filtering / Bulk storage	50% or lower (e.g., 12V → 25V)
General decoupling	60% ~ 70%
High reliability (Automotive, Industrial)	20% ~ 30% (aggressive derating)
Class 1 (C0G/NP0)	Little or no derating needed

A Simple Rule of Thumb

Working Voltage ≤ Rated Voltage × 0.5

That is:

5V circuit → choose 10V or higher (16V / 25V recommended)

12V circuit → choose 25V or 50V

24V circuit → choose 50V

4. Consequences of Not Derating

4.1. Insufficient Effective Capacitance

Increased power ripple

Poor chip decoupling → possible resets or erratic behavior

Degraded EMI/EMC performance

4.2. Accelerated Effective Aging (Relatively Speaking)

DC bias doesn't directly accelerate aging, but with already reduced capacitance margin, further aging over time can push the system to the edge of failure.

4.3. Reduced Reliability

Higher electric field stress inside the MLCC increases the risk of short-circuit failure, especially for larger case sizes.

5. Common Misconceptions About Derating

❌ Misconception 1: "Rated voltage just needs to be higher than working voltage"

Many engineers check only "rated voltage > working voltage" and ignore the DC bias effect.

Correct approach: Always check the actual effective capacitance at your working voltage.

❌ Misconception 2: "All MLCCs need the same derating"

C0G/NP0: DC bias effect is tiny — little or no derating needed.

X7R / X5R: Must be derated.

❌ Misconception 3: "More derating is always better"

Excessive derating (e.g., using a 100V cap for a 5V circuit) leads to:

Larger footprint

Higher cost

Lower available capacitance for the same case size

Recommendation: Derate to 50%~30% of rated voltage — no need to go extreme.

6. Quick Reference: Derating Recommendations by Working Voltage

Working Voltage	Recommended MLCC Voltage Rating (Class 2)
1.8V	6.3V or 10V
3.3V	10V or 16V
5V	16V or 25V
12V	25V or 50V
24V	50V
48V	100V

7. What If You Cannot Derate?

In space-constrained applications (smartphones, wearables), larger high-voltage packages may not fit.

Alternatives:

Use the same voltage rating but a larger case size
Example: 0402 10V → 0603 10V — DC bias performance improves.

Switch to C0G/NP0
If capacitance is low ( <10nF ), C0G eliminates the DC bias issue entirely.

Use multiple MLCCs in parallel
Helps distribute voltage stress, but improvement is limited.

Switch to tantalum or polymer capacitors
But note: tantalum also requires derating (even more aggressively than MLCC).

 

For Class 2 MLCCs (X7R/X5R), never operate above 50% of rated voltage — otherwise effective capacitance collapses.

 

5V circuit → at least 10V, ideally 16V/25V

12V circuit → 25V minimum

C0G capacitors need little or no derating