Feature: Power
usually 12 volts DC (VDC), to meet the requirements of the IT equipment. Finally, within each piece of equipment, the voltage is further regulated to lower levels, often between 1.1 and 5 volts, to power the individual components such as processors and memory modules. Each step in this chain introduces losses that can significantly
impact the data centre’s overall efficiency. Data centre power designers are increasingly adopting wide-bandgap (WBG) semiconductors like gallium nitride (GaN) to minimise losses in the later conversion stages. Compared to traditional silicon (Si), WBG devices achieve superior efficiency through higher switching frequencies and lower conduction losses. However, the capacitor technology used in these converters
presents significant design challenges. Power system designers have traditionally had two proven capacitor technologies: conventional aluminium electrolytic capacitors, which feature low leakage current, and polymer capacitors, which have outstanding ESR characteristics. Panasonic’s EEH Series hybrid aluminium electrolytic capacitors (Figure 1) present a third option that combines the strengths of both to minimise losses due to leakage current and ESR. Hybrid capacitors have other advantages, including enhanced
reliability through open-circuit failure modes and maintaining their rated capacitance at much higher frequencies than traditional designs. While conventional capacitors begin to lose effectiveness at frequencies in the tens of kilohertz (kHz), hybrid capacitors retain their performance at frequencies approaching 1 megahertz (MHz). This higher operating frequency enables the use of smaller capacitors, allowing designers to create more compact converters or free up board space for additional features. A typical hybrid capacitor example is the EEH-
ZA1V151P. This 150 microfarad (µF), 35 volt device maintains a low ESR of 27 milliohms (mΩ), has an operating temperature range of -55°C to approximately +105°C, and features a lifespan of 10,000 hours (hrs) (at +105°C). Its suitability for data centre applications is demonstrated in the EVLMG1-250WLLC DC/DC converter evaluation board from STMicroelectronics (Figure 2). This GaN board achieves power densities of 20 watts per cubic inch (W/in.³) at better than 92 per cent efficiency.
Advantages of low-ESR capacitors for high-density, high-efficiency power delivery The trend toward high-power-density DC/DC converters in data centres creates unique thermal management challenges. The increasing power density and reduced component area can dramatically raise operating temperatures. Minimising a capacitor’s ESR can partly address these
thermal challenges. Since power loss follows the I²R relationship, reducing the resistance directly decreases power loss and, consequently, heat generation. This makes low ESR crucial for maintaining safe operating temperatures in compact designs.
Figure 3: Shown is a selection guide for hybrid capacitors based on ripple current, capacitance, size and operating temperature. (Image source: Panasonic)
However, even the most effi cient capacitors can experience
high operating temperatures due to their environment. T us, selecting a capacitor that can withstand the heat of a tightly packed data centre is essential. Figure 3 shows a selection chart that factors in the operating temperature, among other considerations. While the high switching frequencies enabled by GaN
technology allow for smaller packages, the capacitor technology must maintain adequate capacitance to handle high ripple currents. With capacitance options from 47 μF to 680 μF and the ability to handle up to 2.3 amperes (A) at 100 kHz, the EEH-ZL Series hybrid capacitors address these challenges. T ey also have guaranteed operation to +135°C and an ESR down to 14 mΩ. An example is the EEH-ZL1E681P 680 μF capacitor, which has an ESR of 14 mΩ and a package diameter of 10.0 mm.
Using high-precision resistors for precise power monitoring DC/DC converters in data centre applications require highly accurate feedback for power control. This is especially critical in GaN-based designs, where even minor errors in duty-cycle feedback can result in dangerous overvoltage or overcurrent conditions. While various current-sensing technologies exist, shunt
resistors are particularly appealing for the space-constrained environments of servers, storage infrastructure and power supplies. However, modern designs' high-power density creates significant challenges for resistive current sensing. The primary challenge lies in thermal stability. Resistance
values can drift significantly as operating temperatures change, potentially compromising measurement accuracy. This makes the thermal coefficient of resistance (TCR) a critical specification. It must be as low as possible to maintain measurement precision across the wide temperature ranges encountered in data centre operations. The Panasonic ERA-8P series resistors (Figure 4) address
these challenges through several innovative features: • An ultra-low TCR of ±15 × 10-6 per degree Kelvin (K) achieved through precision thin-film processing
www.electronicsworld.co.uk February 2025 23
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