Capacitor types: MLCC, electrolytic, tantalum
Even at the same 10 µF, size, life and frequency behaviour differ by type. An MLCC in particular loses a lot of capacitance under DC voltage.
| Type | Advantages | Disadvantages | Where used |
|---|---|---|---|
| MLCC (ceramic) | Small, low ESR, good at high frequency | Capacitance drops with DC bias | Decoupling, converters |
| Aluminium electrolytic | Large capacitance cheaply | Large; life is sensitive to temperature | Bulk at the power input |
| Tantalum | Small and stable | Fails short on overvoltage or reverse voltage | Bulk where space is tight |
| Polymer | Very low ESR, long life | Expensive | High-performance supplies |
The MLCC trap: DC bias
An MLCC with an X5R or X7R dielectric drops to half its capacitance or less with a DC voltage near its rating. A 0603, 6.3 V, 10 µF part with 5 V across it may have an effective capacitance of about 3 µF. Check with the manufacturer's simulator (Murata SimSurfing and the like), and go up one step in voltage rating and size.
Dielectric codes
- C0G (NP0): almost no change with temperature or voltage. For filters, timing and crystal load capacitors. Small capacitance
- X7R / X5R: general purpose. Decoupling
- Y5V: varies so much that it is usually avoided
Electrolytic capacitor life
Life halves for every 10 °C rise in temperature. A part rated 2000 hours at 105 °C lasts about 32,000 hours at 65 °C. Do not put it next to a heat sink.