Application Note

VISHAY SPRAGUE
www.vishay.com
Capacitors
Application Note
Capacitance Change with Applied DC Voltage
CONCLUSION
Vishay’s MicroTanTM capacitor is a better choice than a multi-layer ceramic capacitor (MLCC) when a circuit’s proper operation
depends on stable capacitance over a range of applied voltage.
BACKGROUND
Tantalum capacitors in general - and Vishay’s 298D/TR8/TM8 MicroTan tantalum capacitors in particular - demonstrate very
stable performance over the DC voltage (bias) applied in an application. At the same time, the majority of capacitors utilizing
ceramic or polymer dielectrics (monolithic ceramic, disc ceramic, MLCC, polyester, film, etc.) demonstrate significant shift in
both directions - sometimes 40 % to 50 % or higher. Refer, for example, to:
http://www.cliftonlaboratories.com/capacitor_voltage_change.html or:
http://powerelectronics.com/passive_components_packaging_interconnects/packaging/705PET21.pdf
The major reason for such a difference is that a ceramic’s dielectric constant significantly changes under applied electrical field
strength variations, while the tantalum dielectric (oxide film Ta2O5) is not sensitive to such changes. The capacitance change
in ceramic capacitors can also be caused by AC voltage.
1.0
298D, 47 μF
0.8
0.6
MLCC, 47 μF
0.2
0
0.8
1.6
2.4
DC Volts Applied
3.2
4
Typical Voltage Coefficient of Capacitance: Tantalum 298D vs. MLCC
Revision: 26-Jan-12
Document Number: 40144
1
For technical questions, contact: tantalum@vishay.com
THIS DOCUMENT IS SUBJECT TO CHANGE WITHOUT NOTICE. THE PRODUCTS DESCRIBED HEREIN AND THIS DOCUMENT
ARE SUBJECT TO SPECIFIC DISCLAIMERS, SET FORTH AT www.vishay.com/doc?91000
APPLICATION NOTE
MLCC, 100 μF
0.4
Application Note
www.vishay.com
Vishay Sprague
Capacitance Change with Applied DC Voltage
This difference in performance was demonstrated at the Electronica 2010 exhibition. Unlike the MLCC device, the tantalum
capacitor maintains its rated capacitance over the entire rated voltage range.
DEMONSTRATION
APPLICATION NOTE
In the following demonstration, side-by-side testing is conducted on an MLCC and Vishay’s MicroTan tantalum capacitor.
Starting at 0 V, the tester applies successively higher bias voltages and measures the effective capacitance of each component.
Each measurement is normalized (calculated ratio of measured capacitance vs. initial capacitance) and the ratio is plotted
against the applied voltage.
Vishay’s MicroTan capacitor maintains its rated capacitance (100 % measured capacitance to initial capacitance) over the
voltage range, while the capacitance of the MLCC device decreases significantly as voltage increases - down to below 50 %.
As capacitance is the primary performance measure of a capacitor, designers of electronic circuits must account for this loss
of capacitance in the MLCC. Therefore, Vishay’s MicroTan is a better choice than an MLCC when a circuit’s proper operation
depends on stable capacitance.
Note
• It should be also taken into account that ceramic capacitors demonstrate some level of piezo-effect under mechanical stress. The higher
the dielectric constant of the ceramic is, the higher the effect level.
Revision: 26-Jan-12
Document Number: 40144
2
For technical questions, contact: tantalum@vishay.com
THIS DOCUMENT IS SUBJECT TO CHANGE WITHOUT NOTICE. THE PRODUCTS DESCRIBED HEREIN AND THIS DOCUMENT
ARE SUBJECT TO SPECIFIC DISCLAIMERS, SET FORTH AT www.vishay.com/doc?91000