Shrinking Footprints in the Landscape of Switching Regulators

The history of non-isolated switching regulators is one of continuous component integration, coupled with increasing efficiency and functionality. This progression has occurred against a background of decreasing output voltages, as load requirements have dropped from 5V to 3.3V, and now to sub-1V levels seen now. Simultaneously, input voltages have risen as well as system power levels increase, necessitating higher bus voltages with consequent lower current draw. Discrete component designs were simplified by IC controllers that integrated the switching transistors, and more recently, even the magnetics as well. Peripheral functions such as fault monitoring, current sharing, synchronization, and sequencing have been increasingly swept into the IC design.

Even from the early days of switching regulator designs, complete packaged converter modules have been available from vendors, offering proven solutions and saving customers the effort and risk of designing their own. This was sometimes a challenging proposition, as more experienced engineers were often hesitant to pay a premium for something they felt they could design themselves. The development time and risk incurred making an in-house design might be tolerated for a product with a long sales life, expected to recoup R&D costs many times over. There was also an element of professional pride in being able to design a switching power supply from scratch.

Today’s landscape is markedly different. Power design expertise is becoming scarcer within OEMs, and the techniques required for optimum performance are highly specialized, sometimes involving processes an OEM might not have in-house, such as the custom molding of ferrite materials. Furthermore, product life cycles are also much shorter, meaning development costs and delays—whether from design optimization or repeated EMC testing—have a far greater impact on the return on investment (ROI) (Figure 1).

Of course, control IC manufacturers do provide extensive application information, often making designs seem deceptively simple. However, these simplified design tools cannot always predict actual circuit requirements under real-world conditions. For example, suggested output capacitance is often far too low for real-life dynamic loads which may swing by a factor of one million between active and sleep states, potentially producing unacceptable voltage jumps (Figure 2).

Inductors are also frequently ‘glossed over’ in application notes, with suggested parts often chosen for best performance rather than optimal cost and practicality. In reality, the selection of an optimum inductor can take many weeks of evaluating performance over temperature, frequency, and load current variations, both static and dynamic. Other parameters, like inductor saturation characteristics and leakage field, can be critical in designs; EMC performance of a completed design often remains a ‘great unknown’ until the circuit is laid out on the end-PCB and final component choices have been made, at which point changes are costly to make. The story is similar with capacitors, with the optimum parts for performance and cost complex to evaluate with vital information such as self-inductance often not adequately documented in the datasheets.

State-of-the-art switching regulator designs achieve their high power density using control ICs that are frequently BGA packages that might be just 2mm x 2mm with a matrix of pads on a tiny 0.4mm pitch. This may not be compatible with a user’s existing PCB assembly process, potentially requiring precision solder paste application and expensive X-ray imaging for inspection to check for shorts or bad joints. Similarly, a converter control IC may need a complex multilayer PCB with filled and buried vias leading to ground planes to efficiently dissipate heat out of the package into the circuit board. If the user does not need this board complexity for other circuitry, a penalty is paid in the PCB manufacturing cost. Using a pre-designed module can circumvent these specialized manufacturing needs.

One might argue that power modules, being general purpose products, may not be the optimal solution for just one specific application, but the latest generations achieve exceptional performance over a wide range of operating conditions. For instance:

• The RPMH series from RECOM includes both a 0.5A and a 1.5A version. The RPMH-0.5 offers an input range of up to 65V, while the RPMH-1.5 supports up to 60V. Both feature a trimmable output between 2.5V and 28V. They come in a compact, EMI-shielded package measuring just 12.19mm x 12.19mm x 3.75mm. With operation possible up to 105°C without forced air cooling (Figure 3), the series is ideal for demanding industrial environments.
• For higher currents, up to 3A, The company’s RPMB series in the same package operates up to 36V input with its output trimmable from 1V to 24V, offering flexibility for various voltage rail requirements.
• A 6A part, the RPM series, is also available,, with a lower maximum input, in the same versatile package size, suitable for space-constrained applications needing robust power delivery.
• For mid-power applications, the RPZ series covers a wide output current range from 0.5A up to 6A, combining efficiency and flexibility in a space-saving design.
• The RPH-3.0 offers 3A output and targets high-performance applications that require a compact footprint and robust thermal handling.
• For even higher current demands, the RPL series provides solutions from 1A all the way up to 20A, making it suitable for applications requiring high current density and precise voltage regulation.

Thanks to extreme integration in these types of modules, there is little manufacturing cost increment to add a comprehensive range of control and monitoring features such as:

• On/off control
• Remote sensing
• Remote trimming
• Soft start capabilities
• Power-good signaling
• Power sequencing

Modules routinely feature robust fault protection against input under-voltage, short circuits, over-currents and over-temperature conditions. It is understood that applications may operate from almost zero current draw (sleep states) to rated maximum (fully loaded) conditions so modules will often incorporate features to minimise light load power consumption while maximising efficiency, with techniques such as phase shedding in multi-phase converter topologies.

For the highest power density, modules utilize advanced production techniques such as flip-chip on leadframe technology with over-moulding. RECOM’s RPX series (Figure 4) is an excellent example, achieving a 4A rating in a tiny 5.0mm x 5.5mm x 4.0mm QFN package with some parts in the range rated up to 95°C ambient at full load without forced air.

The RPX series is an example of a part that requires external capacitors to function to specification. This can actually enhance overall power density as, for example, input capacitors may already be present on the supply and output capacitors can be precisely chosen for the exact voltage rating required. If these were internal, they would need to be oversized, rated at the maximum possible trimmed-up voltage, consuming valuable space.

On-board regulators often need to be able to boost as well as drop voltage (buck-boost capability). A typical application is in battery-operated equipment where power needs to be maintained for as long as possible as the battery discharges. Traditional solutions like SEPIC, ZETA or Cuk converters, all needing two magnetic elements and involve complex control loops. Modern modular converters, with their degree of integration, can implement a different topology like the four-switch buck-boost at low cost.

This topology effectively uses an array of MOSFETs which can be configured ‘on-the-fly’ as switches or diodes to seamlessly switch between buck and boost modes. The RECOM RBB series is an example featuring up to 4A rating in an LGA package and even a 3kW part in a half-brick format with a wide 9V to 60V input and 0V to 60V output. Typical applications for this part would be 48V to 24V or 12V to 24V battery power conversion, electric vehicles, battery voltage stabilisers or high-power laboratory DC power supplies.