22 POWER CAPACITORS www.empowersemi.com Issue 4 2023 Power Electronics Europe www.power-mag.com layers separating the processor die pins and the PCB (see figure 4). A de-coupling capacitor located on the PCB is thus separated by impedance contributed by the many steps to reach the processor die pins. De-coupling capacitors on the processor die are limited in capacitance and are meant to de-couple the transients with signatures exceeding 1GHz. Capacitors placed on the PCB will see at least two levels of RL impedances to get to the pins of the die. Since E-CAPs demonstrate low ESL and superior de-coupling capability up to many 100s of MHz, their ideal location should be on the SoC package, so that they see minimal impedance to the processor die pins. Silicon capacitors can be realised in profiles down to 50µm and therefore capable of being located within the processor package in tight spaces such as the ball-height of the package, or even embedded within a package substrate which would provide the lowest possible impedance to the processor pins (apart from the on-chip capacitance themselves). High frequency integrated voltage regulators Another notable trend for DC/DC converters used in high performance applications are integrated voltage regulators (IVRs). IVRs leverage high switching frequency techniques in DC/DC converters, enabling orders of magnitude higher bandwidth, and fast response to load steps with minimal droop and recovery. Often neglected at low frequencies, the ESR and ESL of the output capacitor become critical design elements for IVRs that operate at high frequencies, in order to minimise noise and ripple. IVRs are meant for PoL (point of load) power, targeting output voltages from 0.4V to 2.0V. Figure 5 illustrates the difference in ripple of solutions that use MLCC vs ECAPs on the output ripple signature of a DC/DC converter operating at 10MHz. In addition, the ripple waveform is smoother, resulting in fewer harmonics limiting the EMI signature of the design. Growth in demand Over the last decade, the demand for high power applications has grown considerably. Use cases such as compute-intensive server boards used for cloud computing, machine learning deployments, the rise of electric vehicles (EVs) and the need for fast, energy-efficient charging stations are just some examples. There is also the need for ever-faster computing and highly dynamic computational workloads in high frequency, high bandwidth systems and in power conversion applications, high frequency switching topologies yield fewer energy losses while reducing the size of the critical supporting inductors and capacitors. With these game-changing technological innovations, power rail decoupling is even more critical than before. The availability of silicon-based capacitors significantly aids the development of these high frequency, high power applications. www.empowersemi.com Figure 5: MLCC / ECAP output ripple comparison at 10MHz, showing the MLCC at 12mV and E-CAP at 7mV. Table 1: Summary of technical differences between a conventional MLCC and a silicon E-CAP.
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