New-Tech Europe Magazine | Q1 2021

become standardized as the DOSA format for higher power SMT converters, with multilayer internal boards and planar magnetics, but also with the expectation that airflow is available for full output power. As modules, these products have a clear advantage over discrete solutions which could not easily fit in the same footprint. At low power however, cost considerations rule- out expensive multi-layer boards and components so the hunt for an ‘IC style’ solution continued. Non-isolated DC/DC switching regulator use has proliferated in ‘buck’ or ‘step-down’ formats, initially often replacing the traditional ‘three-terminal’ linear regulators, but now used widely as higher input voltage Point-of- Load regulators, providing a set of precise low-voltage rails for highly integrated ICs such as CPUs GPUs and SoC devices. Again, to confer a benefit over discrete solutions, a DC/DC switching regulator should occupy the absolute minimum footprint and height and run cool while meeting the exacting regulation and noise requirements of modern ICs. To achieve this small size implies high efficiency, which traditionally has meant low switching frequency and a consequently large output inductor – exactly the opposite of what’s needed. However, improved semiconductors, converter topologies and magnetic materials have allowed frequencies to push into the MHz range while maintaining excellent efficiency with a small integrated inductor. This has allowed converter designers to be creative with the packaging and achieve astonishing miniaturization, even with an integrated inductor Isolated and non- isolated package technologies vary

Figure 1: Flip chip on leadframe construction in the RECOM RPX series

which utilizes plugged and blind vias for good thermal conductivity and efficient use of the available space, along with an integrated inductor. Construction is a four- layer PCB enclosed by six-sided metallic shielding for low EMI. This type of construction is low profile, but needs a little over 1.4 cm² of real estate to allow proper heat dissipation in order to deliver full power at ambient temperatures exceeding +85°C. The advantage of the RPMB/ RPMH design is that the complex construction is all inside the module. The end-user can use a low- cost two-layer PCB without using expensive plugged vias, yet still be able to utilize a high performance, very compact, SMT on-board power supply without resorting to forced air (fan) cooling. There are three RPM series available, all with identical pad designs so that they are interchangeable:

in the package. For example, the RECOM RPX series has a footprint of just 4.5mm x 4mm and 2mm high in a QFN package, yet provides up to 2.5A of output current at a peak efficiency of over 90%. The 1A version is even smaller, just 3mm x 5mm x 1.6mm high. This power density is achieved with a low-cost flip-chip on leadframe and integrated-inductor construction with over-molding, with the added benefits that the tight switching current loops generate very low EMI, along with high power density and optimized thermal performance, in a QFN package, that cannot be matched by a discrete solution. At higher powers, the RECOM RPMB/RPMH series are examples of 30W buck or step-down DC/DC switching regulators in a thermally- enhanced 25-pad LGA package 11.7mm x 12.19mm x 3.75mm high. This power density is achieved with a multilayer internal PCB

Series Input Voltage Range Output Voltage Output Current Options RPM Up to 15V Up to 17V 3.3V or 5V, trimmable 3.3V or 6V, trimmable 1A, 2A or 3A 6A

3.3, 5, 12, or 15V, trimmable 3.3, 5, 12, 15V or 24V, trimmable

RPMB Up to 36V

2A or 3A

RPMH Up to 65V

0.5A

Figure 2: Summary of RECOM RPM/RPMB/RPMH series specifications Evaluation boards are also available to permit rapid prototyping or to confirm the performance in the end application.

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