In part 1 of the blog we reviewed the characteristics of Class I and Class II multilayer ceramic capacitors (MLCCs) to determine which provided the best performance for high power density applications including snubbers, DC-LINK and resonant converters.
Class I MLCCs including C0G, NPO and U2J came out on top. They are proven to have high temperature stability, low loss and high ripple current capability, making them the first choice for high power density applications.
But what are the latest Class I solutions? Here we’ll delve deeper into Class I technologies that are enabling engineers to make their devices more efficient.
We have recently introduced the surface mount KC-LINKTM 3640 220nF 500V capacitors which are designed specifically to meet the growing demand for fast switching semiconductors that operate at higher voltages, temperatures, and frequencies. The ceramic capacitor uses a CaZrO3 dielectric material and provides a very low-loss solution with ESR values below 4 mΩ from 40 kHz to 1 MHz and as low as 2 mΩ around 50 kHz. This allows for typical ripple currents around 20 Arms from 50 kHz to 300 kHz at 0V DC bias at 105°C ambient.
In addition to KC-LINK’s excellent power handling capability, it’s CaZrO3 dielectric also boasts almost a 2x Modulus of Rupture (MOR) compared to Class II BaTiO3 dielectrics. This gives KC-LINKTM high mechanical robustness and negates the need for a lead frame, thus creating a very low inductance solution (<1nH). With an operating temperature of 150oC, these MLCCs can be mounted near the wide bandgap (WBG) power switches with little need for cooling conserving power and increasing efficiency. Figure 1 shows its impedance, ESR and ripple current.
Figure 1: KC-LINKTM Impedance, ESR, and Ripple Current
Applications often require higher levels of capacitance than high performance Class I dielectrics can achieve, and this requires increased board area. But, with increasing board area comes a reduced power density of the solution. We have developed KONNEKTTM technology – a leadless multi-chip solution design for high efficiency and high-density power applications – precisely to address this problem. KONNEKTTM uses transient liquid phase sintering (TLPS) process to combine Class I MLCCs which can be mounted using standard reflow practices.
Let’s take a look at an example of how this technology is providing high power handling capability:
Three U2J 0.47µF 50V 1812 MLCCs can be joined in ‘standard orientation’ using KONNEKTTM technology and provide a capacitance of 1.4µF in the same footprint as a single MLCC, as shown in figure 2. Further benefits can be achieved by placing the assembly on its side – known as ‘low-loss orientation’ – whereby lower ESR, lower thermal resistance and inductance (ESL), and ultimately higher power handling capability can be achieved.
Figure 2: (Top) KONNEKTTM Technology for Increasing Capacitance in the Same Footprint (Bottom) Standard vs Low-Loss Orientation
Using the U2J 1.4 μF KONNEKT capacitor, ESL is 1.6nH when mounted in standard orientation, reducing to just 0.4nH in low-loss orientation. Similarly, the ESR is reduced in low-loss orientation (from 1.3mΩ to 0.35mΩ) which reduces system losses and limits the temperature rise in the component.
Furthermore, during a ripple current test at 20Arms, infra-red thermal imaging has shown a temperature of 65°C for standard orientation but only 35°C in the low-loss orientation, as can be seen in Figure 3. As a result, current handling is reduced to 11.0Arms in standard orientation, while 34.0Arms is achievable with low-loss orientation.
With very low ESR and extremely high ripple currents, the KONNEKTTM U2J capacitor is ideal for LLC resonant converters specifically designed for data centers, wireless charging, and automotive applications. In the low loss orientation less electrical energy is converted to heat so improving energy efficiency.
Figure 3: (Left) KONNEKT U2J Thermal Imaging Comparing Standard/Traditional vs Low-Loss Orientation During 20Arms ripple current. (Right) Electrical Characteristics
Energy efficiency is high on the agenda in today’s world as it reduces operating costs for significant power usage including automobiles and data center applications. Most of the development effort to date has focused on circuit topologies and semiconductor performance, but passive components such as capacitors are now proving that they have a significant positive impact on power efficiency.
At KEMET we’re dedicated to researching technologies that further increase power handling capability, thereby enabling power engineers to improve efficiencies of their systems.