3D Power Packaging® for Low Power DC/DC converters

Although millions of this style of through-hole DC/DC converter are sold each year, a long-term goal for RECOM has been to develop versions which can be handled, placed and soldered like any other modern SMT component, but also with a low profile to match today’s slim-line products. However, the footprint must still remain small to realize the advantages of a module over a discrete design. To achieve this, non-isolated DC/DC switching regulators and isolated converter modules have to utilize the Z direction by integrating 3D assembly techniques.

The RECOM RPH-3.0 is a compact 3A power module, encapsulated within a space-saving 10 x 12 x 4mm QFN SMD package. Embracing RECOM’s '3D Power Packaging' philosophy, this module integrates a shielded inductor and employs flip-chip mounting for its control IC, ensuring superior electrical and thermal efficiency.

This module boasts a very wide input voltage range spanning from 4.5V to 55V DC, accommodating various power sources such as 36V or 48V li-Ion batteries or 5V, 12V, 24V, or 48V power supply rails. Users can conveniently configure the output voltage within the range of 1V to 15V using two resistors, while the operating frequency, ranging from 100kHz to 1000kHz, can be set with a single resistor.

Equipped with comprehensive features, including on/off control, a power good signal, soft-start functionality, and robust protection mechanisms against short circuits, over-voltage, over-temperature, and overload, this module ensures reliable operation. Even under demanding conditions, it maintains operational integrity, capable of withstanding ambient temperatures of up to 125°C with appropriate derating.

At higher powers, the RECOM RPMB/RPMH series are an example of a 30W part 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 which utilizes plugged and blind vias for good thermal conductivity and efficient use of the available space.



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 RPM/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:

Non-isolated DC/DC switching regulator use has proliferated in ‘buck’ or ‘step-down’ formats, initially replacing inefficient ‘three-terminal’ linear regulators, but now widely used as onboard point-of-load (PoL) regulators to provide a set of local low-voltage rails for highly integrated ICs such as CPUs, GPUs and SoC devices. Ideally, such on-board PoL regulators should meet the exacting regulation and noise requirements of modern ICs, yet still run cool under full load. To achieve the required high efficiency has traditionally meant relatively slow switching frequencies and a consequently large output inductor – exactly the opposite of what’s needed to have the absolute minimum footprint and height dimensions. However, improved semiconductor technologies, advanced converter topologies and better magnetic materials have allowed switching frequencies to be moved up into the MHz range while still 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 the inductor integrated inside the package. For example, the RECOM RPX series have a footprint of just 4.5mm x 4mm in a 2mm high QFN package yet provide up to 4A of output current at a peak efficiency of over 90%. The 1.5A RPY-Q is even smaller, just 3mm x 5mm x 1.6mm high. This high 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. The RPY-Q and RPX-Q variants are also qualified to the automotive standard AEC-Q100, including optional ‘wettable’ flanks for automated optical inspection of solder joints.

The RPL-1.0, RPL-3.0 and RPL-5.0 are power modules with integrated inductor in a tiny 3 x 3mm LGA package. Despite their small size, they are complete power modules, requiring only input and output MLCC capacitors and two output voltage setting resistors to create a fully functioning power supply. For the 3A and 5A versions, a sense input compensates for any I²R losses in the output tracks, while all versions feature enable and power good connections to permit simple power rail sequencing in distributed power architecture applications. An internal LDO regulator provides a fixed 3.3 VDC/20mA output suitable for pull-ups or external control logic.

The higher current RPL-10 and RPL-20 are power modules with integrated inductor in a compact 7 x 7mm LGA package. Despite their small size, they are complete power modules, requiring only a few passive resistors and capacitors to create a fully functioning power supply. The RPL-10 and RPL-20 feature enable, tracking and power good connections to permit simple power rail sequencing in distributed power architecture applications, as well as adjustable operating frequency and start-up times.

The RPL series use constant on-time control for a fast reaction to abrupt load transients combined with a separate slow control loop for output stability, offering precise load regulation without compromising on transient response. This makes them especially suitable for powering highly dynamic loads such as microcontrollers, radios or pulsed current imaging systems.

The RPZ-0.5 and RPZ-1.0 versions in 2mm x 2mm QFN packages accept an input voltage range from 2.3V up to 5.5V, allowing 3.3V or 5V fixed supply voltages or a single Li-ion cell to be used. The 0.5A or 1A output voltage can be set with two resistors in the range from 0.6VDC up to 5.25VDC. The RPZ-2.0 and RPZ-3.0 versions in 2.5mm x 3.5mm QFN packages accept an input voltage range from 2.75V up to 6V, allowing 3.3V or 5V fixed supply voltages or a single Li-ion cell to be used. The 2A or 3A output voltage can be set with two resistors in the range from 0.6VDC up to 5.5VDC. The RPZ-6.0 version in a 4 x 6mm QFN package accepts an input voltage range up to 7VDC and down to 2.75VDC, allowing 3.3V or 5V fixed supply voltages or a single Li-ion cell or a 6V battery to be used. The 6A output voltage can be set with two resistors in the range from 0.6VDC up to 6.65VDC.

The RPZ series internal controller uses constant on-time control for a fast reaction to abrupt load transients combined with a separate slow control loop for output stability, offering precise load regulation without compromising on transient response. This makes them especially suitable for powering dynamic loads such as microcontrollers, radios or pulsed current imaging systems.

The RS12-Z series of DC/DC converters achieves class-leading power density in a SIP8 format by leveraging off planar transformer technology with advanced packaging and thermal design. In a metal case, the series features high efficiency and operates at full 12W load to 75°C with convection cooling only (24V input). Pinout is industry standard with backwards-compatibility to 3W and 6W parts in the SIP8 format, for an easy power upgrade. Minimal external filtering is required to achieve EN 55032 EMC compliance, class A or B. The parts also include an output trim function and input under voltage lockout as well as continuous short circuit protection.

The parts are ideal when a wide input range is required, covering multiple nominal voltages.

These DC/DC converters feature a 3D packaging technique that is unique to RECOM. A custom plastic moulding supports the control PCB which forms the top surface of the part, while the isolation transformer mounts underneath to achieve a minimum footprint overall, with a height between 5.8 and 8.5mm depending on family. The open-frame construction has particular value when surface-mount reflow profiles are too severe for potted or moulded parts. The R1SX series provides a single output at 1W up to 100°C while the R1DX provides dual outputs. Both parts are agency-certified with 3kV/1 second isolation. The R1ZX series is similar to the R1SX but includes a linear regulator for a precise, low noise output with 2kV/1 second isolation. The R2SX series provides 2W up to 75°C (100°C with derating) and withstands 3kV/1 second.

All devices in this packaging format have industry standard and compatible pin-outs and are ideal for use in bus isolators, industrial controls and battery management systems.

The examples described so far have been non-isolated converters. When safety agency certified isolation is required, besides voltage withstand, minimum creepage and clearance distances are defined. For example, in medical applications with mains system voltages, 8mm creepage is required between input and output for two Measures of Patient Protection (2MOPP). Given this minimum packaging dimension, a more traditional approach can be taken, with an internal die comprised of a power chiplet and control chiplet wire-bonded to a DVE SOIC-16 leadframe, then conventionally over-molded, such as in the RECOM RxxCT(E) and RxxC05TE parts. The transformer in these DC/DC converters is a proprietary, very low profile, planar-type design, achieving up to 5k VAC/1min isolation voltage and reinforced, 2MOPP isolation. The overall height of these parts is only 2.50-2.65mm, making them suitable for card-type applications as the height of the isolated DC/DC converter is not higher than all of the other SMT components. The RxxCT(E) and RxxC05TE series are available in cut-tape (-CT) or tape-and-reel (-R) packaging options.

The isolated SMD DC/DC converter RxxC1TFxxS comes in an ultra-compact 5mm x 4mm x 1.2mm LGA package. The input voltage range covers both 3.3V and 5V rails and the regulated and protected output is pin selectable for 3.3V or 5V. The part offers 3kVAC/1s isolation, and a wide operating temperature range from -40°C up to +80°C without derating. The fully automated manufacture makes it particularly suitable for high-reliability industrial applications, such as isolated communication ports, industrial automation, IoT applications, and sensor isolation.