Q.Ripple current of MLCC (4): How is the allowable ripple current measured?
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There is no industry standard on how to measure allowable ripple currents. TDK specifies a maximum increase of 20°C from ambient temperature due to ripple current for all MLCCs. In actuality, increases in temperature are estimated indirectly when the ESR of MLCCs and thermal resistance are measured. Joule heating continues to warm an MLCC as long as the ripple current flows, but the part will also radiate heat, which cools the part. Temperature increases are determined with the balance between this heat generation and heat radiation.
The ratio of the amount of heat generation per unit time and temperature increase is called thermal resistance, and if the MLCC case sizes and material are the same, they will have the same thermal resistance. Therefore, if the ESR is known, the amount of power dissipation per unit time can be calculated. The amount of increased temperature can be calculated by multiplying the power dissipation figure with the thermal resistance. The maximum ripple current allowed for a temperature increase of 20°C is calculated with this method to find the allowable ripple current.
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