MLCC DC Bias, Aging & Selection Guide for Engineers
Have you ever picked a 10µF MLCC, soldered it in, and measured 3µF under DC bias? The capacitor isn't defective. The physics is working against you.
Why MLCC Capacitance Drops Under DC Voltage
MLCCs use ceramic dielectrics based on barium titanate (BaTiO₃). When you apply a DC voltage, the crystal lattice polarizes and loses its ability to store charge. This is measured as capacitance derating under DC bias.
Class II dielectrics—X7R, X5R, Y5V, Z5U—all suffer from this effect. The higher the dielectric constant, the worse the drop. A Y5V capacitor can lose 90% of its rated capacitance at just half its rated voltage.
Class I C0G/NP0 capacitors are immune. If your circuit needs stable capacitance regardless of voltage, C0G is the only choice.
How Bad Is It?
| Dielectric | Capacitance Change Under Bias |
|---|---|
| C0G/NP0 | Zero |
| X7R | 15-30% loss typical; up to 50% at rated voltage |
| X5R | 30-50% loss typical; severe above 50% rated voltage |
| Y5V/Z5U | 70-90% loss at half rated voltage |
At 80% of rated voltage, a 10µF X5R capacitor might deliver only 3-5µF. Murata, TDK, and Taiyo Yuden all publish DC bias curves—check them before committing to a design.
MLCC Aging: Why Your Prototype Drifts
Class II MLCCs lose capacitance logarithmically over time, even sitting on a shelf. This is called aging:
C(t) = C₀ - m · log₁₀(t)
where m is a percentage loss per decade-hour (a factor-of-10 change in time).
| Dielectric | Aging Rate (%/decade hour) |
|---|---|
| C0G/NP0 | ~0% |
| X7R | ~1% |
| X5R | ~2% |
| Y5V | ~5% |
An X7R capacitor measured 1 hour after manufacturing will lose about 1% at 10 hours, 2% at 100 hours, and 3% at 1,000 hours. The process is reversible: heating above the Curie temperature ("de-aging") resets the capacitance to its original value, which is why your board works differently after reflow soldering than a week later.
Selecting MLCCs for Real Applications
Power Supplies and DC-DC Converters
Input capacitors handle the hardest job. MOSFET switching produces di/dt rates 100× the output section. A 6A buck converter at 300kHz needs input capacitors that can handle 2.6A RMS ripple current near the switch.
Use X7R or X5R MLCCs at 2-3× the expected DC voltage to minimize bias loss. For a 12V rail, choose 25V or 35V rated parts. Place them as close as physically possible to the switching FET.
At Movthing, we stock MLCCs from TDK, Murata, and Taiyo Yuden in 0603 through 1210 packages for power applications.
Automotive Electronics
AEC-Q200 qualified MLCCs use soft-termination (flexible end-terminations) to survive thermal cycling and PCB flex. Standard MLCCs crack under vibration and board bending—automotive-grade parts add conductive resin layers that absorb mechanical stress.
For under-hood applications (-40°C to +125°C), X7R or X8R dielectrics are mandatory. X8R extends the upper temperature to +150°C. Browse automotive-grade MLCCs for AEC-Q200 qualified parts.
Precision Analog and Timing
Use C0G/NP0 MLCCs. Zero DC bias shift. Zero aging. Negligible dissipation factor (<0.1%). Capacitance values range from 0.5pF to ~0.1µF. These are ideal for oscillators, filters, sample-and-hold circuits, and any application where capacitance stability matters.
C0G parts have lower volumetric efficiency—a 100nF C0G 0805 is about the practical limit—but for precision circuits, stability beats density.
The Equivalent Circuit Your SPICE Model Needs
Every MLCC is actually an RLC circuit:
- ESR: Equivalent series resistance. Varies with temperature, frequency, and DC bias. Dictates ripple heating.
- ESL: Equivalent series inductance. Around 1nH for 0603 packages. Limited by package geometry, not capacitance value.
- C: The capacitance, which depends on DC bias, temperature, and aging.
Above self-resonant frequency (SRF), the capacitor becomes inductive. For high-speed decoupling, a 0402 or 0603 with reverse-geometry terminals (wider, shorter) halves the ESL to ~500pH.
Quick Selection Checklist
- What DC voltage will the capacitor see? Derate Class II parts by 2-3× voltage for power applications.
- What temperature range? X7R for -55°C to +125°C. C0G for precision.
- Is the PCB subject to flex or vibration? Use soft-termination automotive-grade MLCCs.
- What ripple current? Calculate ESR losses at switching frequency.
- Timing-critical? Use C0G—zero aging drift.
Need help finding specific parts? Request a quote or browse our MLCC catalog with 3,700+ part numbers across 8 manufacturers.