As an essential factor in circuit design, the equivalent series resistance (ESR) is a measurement of all non-ideal resistors in series with the capacitor。When multilayer ceramic capacitors (MLCCWhen there is a current passing through at AC voltage, its own due toESRThe resulting losses generate heat, which can cause performance and reliability problems in today's more complex and smaller circuit systems。

Similarly, the quality factor (Q) is also a measureMLCCImportant parameter of。和ESRAgain, the quality factor is frequency dependent and difficult to measure accurately over the entire frequency range。At the same time, the relevant measurement work needs to verify the data provided, so it is difficult to directly compare the data provided by different companies。

One thing is certain, however——The measured value depends to a large extent on the resistance of the conductor plate, insulation material, end, etc。ESRThe higher the value, the greater the energy loss of the capacitor——Refer to the following equation:

其中RsIs equivalent series resistanceESR(unit: ohms),DFIt's a dissipation factor,XcIs capacitive reactance (unit: ohms)。 

Equivalent series resistance (ESRIt also determines how much of the ripple current will be converted into heat energy。As mentioned above, if the power dissipation problem is not handled properly, the high temperature can adversely affect the performance of the capacitor and may lead to accidental damage to the components during long hours of operation。

其中PIs power dissipation (in watts);IIs the root mean square current (in amperes);RIs equivalent series resistanceESR(Unit: Ohm)。

Equivalent series resistance (ESRMeasurements can be made in two ways:

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Using a resonant tube, its resonant frequency and bandwidth are dependent on the quality factor of the capacitorESRInfluence of。

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或 

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Sweep frequency measurement with impedance analyzer, which can directly measure the characteristics, but also has more inherent poor contact problems。

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To be clear, the capacity and operating voltage areMLCCWith two defining parameters, good control of materials and design means consistency in capacitor performance——Although the actual values measured may vary。

One more thing to note，When comparing data obtained from different sources, or data obtained during different time periods of testing，May not truly reflect the actual performance of the component in the circuit;It also needs to be taken into account，These test data are obtained from the components installed in the test fixture，Therefore, it is not fully representative of the actual component performance welded in the circuit。

In addition, the suitability of the component for the relevant application also needs to be confirmed by the evaluation of the circuitESR值和QThe purpose of values is precisely to be rightMLCCPerformance in a specific operating frequency range is given as a reference。

Understand equivalent series resistance (ESRThe value is critical because it determines whether the component is suitable for RF power applications。如果ESRIf the value is too high, the self-heating caused by loss will be too large, and the component will fail due to overheating。凭借ESRThe value can also calculate the maximum rated current that the component can withstand。

It is worth mentioning that in high ripple current applications, the equivalent series resistance (ESRThe impact is also significant——For example, in a series of related applications such as electric vehicles, filter capacitors and flat flow capacitorsESRThe value is the key consideration。

Capacitors are essential passive components in circuit design。Nowadays, there are so many capacitor specifications to choose from that it is not an easy task to determine which capacitor is best for your application。At the beginning of circuit design, engineers need to decide whether to use single-layer capacitors(SLCOr multilayer ceramic capacitors (MLCC) to meet application requirements。

Overall, the two seem to have similar functions, as eitherSLC还是MLCCAll of them can be used as charge storage, filter or bypass in the circuit。To determine which one best fits your needs, let's start with their basic structure。SLCIt is the most basic type of capacitor, with only one layer of dielectric material or insulating layer between the positive and negative electrodes。

MLCC基于SLCThe basic principle of the design is obtained by embedding multiple layers of electrodes in the dielectric of a single capacitorMLCCThe tolerance value is equivalent to multipleSLCCapacity used in parallel。Although in terms of thickness,MLCC比SLCIt is slightly thicker, but it can achieve more capacity in a smaller volume——This is precisely the current assessment of the size, weight and power of capacitors.SWaPKey factors that need to be considered for RF and microwave applications。图1Have displayedSLC与MLCCBasic structure of。

图1. The picture on the left isSLCThe structure, shown on the right isMLCCStacked hierarchy。

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SLCSuitable application scenarios

SLCIt is specially designed for microwave and RF applications。This is becauseSLCInherent self-resonant frequency(SRFThat is, the point at which the capacitor will exhibit the minimum impedance)It is the highest discrete block fixed capacitor。

It's worth noting that, in generalESR (That is, the internal resistance in series with the capacitor) Varies with frequency, so use is lowESRThe capacitors are very necessary。In addition, due toSLCIt is a monolithic integrated form that contains a limited number of mechanical components, which also helps to reduceESR值。

然而，SLCThere is one potential drawback——Since it is only a single layer structure, the capacitance value depends largely on the permittivity of the dielectric used, which limits to some extent the maximum capacitance value that can be obtained。因此，SLCIt is mainly suitable for high frequency and low capacity applications。Lou capacitanceKPD）是为LCThe filter market is a leader in providing custom high value parallel plate capacitors。

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MLCCSuitable application scenarios

Generally speaking,MLCCThe tolerance range ratioSLCIt is much higher, so it can be used in various situations。MLCCIt is composed of multiple layers of dielectric and electrode, which can withstand higher operating voltage in addition to higher capacitance value——Lou capacitanceKPD) manufacturedMLCCAt present, the highest pressure can be reached12kV。However, because of the use of multiple layers of electrodes and dielectrics,MLCC的ESRNormal ratio of valuesSLCMuch taller。因此，MLCC（含高QValue, ultra-low loss primary dielectricMLCC), can only be dealt with30GHzBelow the frequency, whileSLCCan handle up to100GHzThe frequency of。

In RF and microwave applications, if there are high requirements for both capacitance and voltage, thenMLCCIs a more appropriate choice;In applications other than RF and microwave applications,MLCC, especially Lou capacitance (KPDManufactured with an innovative designMLCCIt is ideal for demanding applications such as medical implants, automotive electronics and high-reliability blasting。

To sum up, becauseSLC和MLCCIn terms of withstand voltage, frequency, capacity and other parameters, it is not interchangeable in application。In short,SLCVery suitable for high frequency, low voltage RF microwave applications, whileMLCCIt can be used in a more limited frequency range for various types of high voltage and high volume applications。