Key Takeaways
- No matter the type, ceramic capacitors are derated to protect against heavy electrical loading and negative effects from applied voltage and temperature.
- Voltage derating involves lowering the working voltage to roughly 50% of the rated maximum to prevent failure.
- Temperature derating means keeping the operating temperature about 15°C below the rated limit to ensure stability and long service life.
Types of Ceramic Capacitors
Multilayer ceramic capacitors (MLCCs) are compact components commonly used in surface-mount technology, EMI or RFI suppression, and feed-through applications. Regardless of the style, ceramic capacitors should be derated to prevent excessive electrical stress caused by voltage and temperature.
Ceramic Capacitor Derating
Engineers derate capacitors to increase reliability, protect against surge currents, and stabilize key electrical parameters. Ceramic capacitors are naturally resistant to moisture thanks to their impermeable material, but they can be less reliable at elevated temperatures. Failures may occur as shorts, opens, or gradual parameter drift. Excessive surge current can cause thermal breakdown and even catastrophic failure. Since electrical parameters like capacitance, ESR (equivalent series resistance), and ESL (equivalent series inductance) all change with voltage and temperature, derating is critical.
Ceramic Capacitor Derating Methods
Derating reduces the stress factors that accelerate failure, making capacitors less prone to breakdown. The main stressors are applied voltage and temperature, which combine to influence how long a capacitor performs reliably. As voltage nears the rated maximum, capacitance begins to drop. Rising temperatures further decrease capacitance in the circuit.
For ceramic capacitors, derating focuses on controlling these two parameters. The most common practice is voltage derating, where the applied voltage is kept around 50% below the rating. Another technique is temperature derating, which sets the maximum operating temperature roughly 15°C below the specified limit. Both methods extend life and preserve performance stability.
Ceramic Capacitor Derating Voltage
Ceramic capacitors are particularly affected by capacitance loss under applied voltage. For example, X7R capacitors can lose up to 80% of their capacitance at full rated voltage due to dipole realignment inside the ceramic. This effect is known as the voltage coefficient of capacitance.
To counter this, it’s best to select capacitors that operate well below their maximum rating. A derating guideline of about 50% ensures more stable behavior. Voltage derating is expressed as a percentage: a 30% derating means the capacitor runs at 70% of its rated value.
A good design rule is to choose a capacitor rated for at least double the applied voltage. Because stored energy increases with the square of voltage, this practice not only improves reliability but also manages energy handling safely.
For both safety and longevity, targeting about 50% of the rated voltage is considered the most reliable approach.