What Capacitance Changes Are Expected with Changes in Temperature?
C0G and NP0 Class 1 ceramic temperature characteristics do not show significant changes in capacitance vs temperature.
Generally, heat lowers Class 2 capacitors’ capacitances, however around the Curie point (approximately 120°C for BaTiO3), the capacitance increases. This is due to an increase in the dielectric constant as the crystal structure of the ceramic changes from tetragonal to cubic.
The EIA and JIS standards state that within the operating temperature range, the change in capacitance will not exceed the specified tolerance. The chemical composition of the ceramic is not a part of the standard. Manufacturers of capacitors use different additives to the dielectrics in order to change the performance of the capacitors. These additives can shift the Curie point closer to room temperature (e.g. Z5U) or smooth the dielectric constant curve (e.g. X7R). The former have the highest unbiased dielectric constants, while the latter lower the maximum dielectric constant in order to achieve greater temperature stability.
These formulations are proprietary, and ensure that not all capacitors are created equal.
Filters are available on our capacitor directory to select products based on varying temperature coefficients (Fig. 1)
Click here to see our full range of MLCCs.
Fig. 1: Digi-Key Filter for MLCC Temperature Coefficients
Below is a graph of several MLCC’s temperature characteristics.
Fig. 2: ATC graph of three 10nF, 50V, EIA0603MLCCs
What Affect Does Temperature Have on ESR?
Temperature itself does not have any effect on ESR. ESR is often represented in the mathematical relationship:
ESR = DFXc = DF/2πfC (Formula 1)
Temperature does affect capacitor performance. The temperature characteristic of the material defines the maximum rated operating temperature of the capacitor. For example, a X7R is defined to operate up to 125°C while a X5R is defined to operate up to 85°C. The total temperature of your circuit environment plus the self-heating (i.e. ripple current) of the capacitor combined cannot exceed the maximum rated temperature of the capacitor. For an X7R, if the circuit operating temperature is 100°C, the ripple current cannot introduce more than 25°C of self-heating.
Content and images provided courtesy of TDK’s FAQ: