On the surface, the process appears logical: mount a 2x2mm controller IC of the latest generation with the manufacturer-recommended components on the PCB to create a fully functioning switching regulator. In theory, this should provide high efficiency, low idle current, and integrated safety and control features at minimal cost. However, in practice, various design complexities arise. As often happens, the devil is in the details.
Why Modular SMD Switching Regulators are More Efficient
Mar 20, 2019
With modern controller chips, designing switching regulators using discrete components should be straightforward. Instead of purchasing pre-assembled modules, manufacturers consider mounting the controller IC alongside the recommended external components directly on the SMD board. While this approach seems practical, real-world implementation reveals several challenges.
Table of contents
Handling Dynamic Loads
The circuits proposed by chip manufacturers typically assume that most loads are static. These designs, therefore, incorporate only a few additional components. However, in practical applications, static loads are the exception rather than the rule. Load cycles with ratios of 1:1 million are common—such as when a microcontroller enters sleep mode.
What happens in a switching regulator when the load current drops instantaneously from several amperes to a few µA? At this point, built-in "intelligence" becomes irrelevant, as fundamental physics take over. Energy stored in the inductor during one half-wave must be transferred to the load in the next half-wave. If the load suddenly decreases to zero, the energy can only be transferred to the output capacitor.
As illustrated in the formula above, excess energy results in a rapid voltage increase in the capacitor. When this occurs, the controller switches the on-time to zero. However, if residual energy remains in the inductor, the output voltage may become unregulated. In low-voltage designs, this could even double the output voltage unless capacitance is significantly greater than what the data sheet recommends.
Addressing this challenge in discrete designs is not simple. Advanced configurations buffer the output with six parallel capacitors (Fig. 1), exceeding typical chip manufacturer recommendations. This setup is standard in RECOM’s RPM series. Using multiple small ceramic capacitors instead of a single large capacitor increases surface area, enabling better heat dissipation from the IC and inductors to the GND plane. Additionally, this configuration reduces ESR.
Fig. 1: The compact RPM module board (1.5cm²) from RECOM features six parallel capacitors, effectively managing extreme load cycles.
What happens in a switching regulator when the load current drops instantaneously from several amperes to a few µA? At this point, built-in "intelligence" becomes irrelevant, as fundamental physics take over. Energy stored in the inductor during one half-wave must be transferred to the load in the next half-wave. If the load suddenly decreases to zero, the energy can only be transferred to the output capacitor.
As illustrated in the formula above, excess energy results in a rapid voltage increase in the capacitor. When this occurs, the controller switches the on-time to zero. However, if residual energy remains in the inductor, the output voltage may become unregulated. In low-voltage designs, this could even double the output voltage unless capacitance is significantly greater than what the data sheet recommends.
Addressing this challenge in discrete designs is not simple. Advanced configurations buffer the output with six parallel capacitors (Fig. 1), exceeding typical chip manufacturer recommendations. This setup is standard in RECOM’s RPM series. Using multiple small ceramic capacitors instead of a single large capacitor increases surface area, enabling better heat dissipation from the IC and inductors to the GND plane. Additionally, this configuration reduces ESR.
Fig. 1: The compact RPM module board (1.5cm²) from RECOM features six parallel capacitors, effectively managing extreme load cycles.
Improving EMC
While discrete designs can address load cycle issues, EMC remains a greater challenge. The effectiveness of an EMC filter depends not just on the controller IC but also on the PCB layout. This is why IC manufacturers typically refrain from providing definitive EMC recommendations. Many device designers lack in-depth knowledge of the interaction between ICs and PCBs, making it difficult to predict whether their circuits will pass EMC tests.
The EMC challenge becomes even more significant at high switching frequencies, as designers must reduce inductor size. Joseph Fourier demonstrated that a square wave consists of an infinite sum of sinusoidal waves at higher frequencies. The higher the switching frequency, the greater the number of harmonics—raising the likelihood of resonance effects within PCB-embedded inductors and capacitors.
Certified modular components are optimized for EMC. RECOM’s RPM series modules, for instance, feature a 4-layer PCB with a bottom shielding layer and metal housing, offering excellent EMC performance (Fig. 2). Their data sheets specify simple SMD ferrite beads, enabling reliable Class A or Class B compliance, verified through RECOM’s EMC lab tests (Fig. 3). Depending on primary power quality and module-to-load distance, additional filtering may not even be necessary.
Fig. 3: Electromagnetic emissions of an RPM5.0-6.0 with external filter components for Class B compliance.
The EMC challenge becomes even more significant at high switching frequencies, as designers must reduce inductor size. Joseph Fourier demonstrated that a square wave consists of an infinite sum of sinusoidal waves at higher frequencies. The higher the switching frequency, the greater the number of harmonics—raising the likelihood of resonance effects within PCB-embedded inductors and capacitors.
Certified modular components are optimized for EMC. RECOM’s RPM series modules, for instance, feature a 4-layer PCB with a bottom shielding layer and metal housing, offering excellent EMC performance (Fig. 2). Their data sheets specify simple SMD ferrite beads, enabling reliable Class A or Class B compliance, verified through RECOM’s EMC lab tests (Fig. 3). Depending on primary power quality and module-to-load distance, additional filtering may not even be necessary.
Fig. 3: Electromagnetic emissions of an RPM5.0-6.0 with external filter components for Class B compliance.
Effective Heat Management
After addressing EMC, designers must consider heat dissipation. Compact modern controller ICs make effective heat management difficult, yet proper thermal design is crucial for longevity and reliable operation in varying ambient temperatures. A 4-layer PCB is the preferred solution, with the GND plane acting as a heat sink. For devices where a two-layer board suffices electrically, using pre-engineered modules is often more cost-effective. RECOM’s RPM series integrates advanced thermal management features, optimized at RECOM’s R&D lab in Gmunden.
These 12x12mm RPM modules incorporate innovative thermal enhancements, such as multiple vias designed as heat pipes. While this technology incurs additional costs, it provides highly efficient heat dissipation from BGA ICs and passive components to the metal housing and GND plane. This results in higher thermal performance, allowing RECOM’s RPM modules to operate at ambient temperatures up to 105°C without derating.
These 12x12mm RPM modules incorporate innovative thermal enhancements, such as multiple vias designed as heat pipes. While this technology incurs additional costs, it provides highly efficient heat dissipation from BGA ICs and passive components to the metal housing and GND plane. This results in higher thermal performance, allowing RECOM’s RPM modules to operate at ambient temperatures up to 105°C without derating.
Advanced Technical Features
The RPM series includes non-insulated SMD switching regulator modules built to modern standards. Current options offer 3.3V and 5V outputs with 1A, 2A, 3A, or 6A currents, with adjustable output voltages between 0.9V and 6.0V via external resistors. The ultra-low-profile design achieves efficiency ratings between 97% and 99%, particularly excelling in the 5% to 20% load range (Fig. 4).
Maximum permissible ambient temperatures are similarly high—e.g., +107°C for the 1A model without external cooling. These modules also include features such as soft start, sequencing, and output voltage tracking. Manufactured in a fully automated European facility, the RPM series is available through standard distribution channels. Pricing for the most powerful model starts at approximately 4 Euro, depending on order volume.
Maximum permissible ambient temperatures are similarly high—e.g., +107°C for the 1A model without external cooling. These modules also include features such as soft start, sequencing, and output voltage tracking. Manufactured in a fully automated European facility, the RPM series is available through standard distribution channels. Pricing for the most powerful model starts at approximately 4 Euro, depending on order volume.
Evaluation Boards for Accelerated Prototyping
Choosing modular DC/DC converters over discrete designs accelerates prototyping. Previous module generations had pin connectors for easy mounting, but modern RPM modules feature 25 pads, each measuring approximately 1mm². To simplify prototyping, RECOM provides dedicated evaluation boards that integrate the switching regulator and external filtering components without soldering.
Conclusion
Although integrated controller ICs enable relatively simple non-isolated switching regulator designs, pre-assembled modules often offer a more practical alternative. They expedite prototyping, lower the risk of EMC compliance issues, and simplify BOM management by consolidating multiple discrete components into a single part. Additionally, modules eliminate the challenge of placing miniature controller chips beside significantly larger components on a PCB.
Applications
