Novel Reference Designs for Small to Medium 50W to 1kW Power Supply SystemsLogiCoA™ power supply solutions replace analog control
with a hybrid analog-digital design - provides the functionality of
fully digital control with the low power consumption of analog

ROHM has recently introduced LogiCoA™, a lineup of power supply solutions designed for small to medium power industrial and consumer equipment (50W to 1kW class) that delivers the same functionality as fully digital control power supplies while maintaining low power consumption and costs equivalent to analog power types.

LogiCoA™ represents the industry’s first ‘hybrid analog-digital control’ power supplies, integrating a digital control block centered around LogiCoA™ MCUs with an analog circuit topology comprised of MOSFETs and other power devices.

Using low-power LogiCoA™ MCUs and power control OS (RMOS) allows ROHM to propose new solutions that overcome challenges previously unachievable with conventional analog control, including design optimizations that considers component variations, enhanced customer complaint response/failure analysis, streamlined lineup/derivative product development, and improved parts inventory management.

Introducing LogiCoA™ Power Supply Solutions

Power Supply Circuits in the Industrial Equipment Market

In industrial power systems, the market for small to medium power applications is expected to grow steadily.

While digital control is prevalent in high power applications, analog-control power supplies are commonly used in switching power systems operating in the small to medium power range of 50W to 1kW.

However, recent demands for higher reliability and more precise control have made it increasingly difficult to meet market expectations with analog-only configurations.

On the other hand, although fully digitally controlled power supplies offer advanced control and settings, they are not widely adopted in the small to medium power range due to the high power consumption and cost of digital controllers.

Current Issues in Power Supply Systems

Switching power supplies are generally classified into two types: analog and fully digital control.

Analog control power supplies utilize analog control ICs to achieve low power consumption, low cost switching power control circuits. However, they function solely as power supplies providing no additional features. They are also highly susceptible to component variability, requiring large design margins for component ratings, which leads to increased costs and larger circuit sizes.

Conversely, fully digital control power supplies process signals using high-speed CPUs or DSPs. This allows software-based adjustments of key parameters such as output voltage, dead time, and protection circuits to compensate for component variability, but issues remain, including high costs and increased power consumption due to the need for high-speed CPU clock operation.

To address these challenges, ROHM developed LogiCoA™ power solutions that blend analog and digital control. These solutions feature a user-friendly design that incorporates the functionality of fully digital control while maintaining the cost effectiveness and low power consumption of analog power supplies.

LogiCoA™ offers four main benefits: high performance, low cost, low power consumption, and easy implementation

Examples of Challenges Addressed by LogiCoA™

Challenge ① Design that accounts for variability

One of the most difficult aspects of switching power supply design is managing the saturation current of components like inductors and transformers. Increasing the current beyond the saturation point can cause the power supply to fail during operation, so it is crucial to limit the current before reaching this threshold. In analog control, the OCP (overcurrent protection) value is set by the IC, but due to variations in power supply voltage and temperature, a design margin of approx. ±30% is typically required to accommodate for these fluctuations.

In contrast, LogiCoA™ power solutions allow the OCP variability to be adjusted during the power supply manufacturing process to as low as ±1%. This enables the use of power components with lower current ratings, contributing to both miniaturization and cost reduction.

Issue ② Customer Complaints/Failure Analysis

When a power supply issue arises, analog control systems cannot determine the state at the time of anomaly, making failure analysis difficult. In contrast, LogiCoA™ power solutions can log data in Data Flash (non-volatile memory), such as input voltage, output voltage, output current, and temperature, using software without impacting power control.

At the same time, a command interface is provided that allows easy retrieval of log data from the MCU, streamlining complaint handling and failure analysis. This makes LogiCoA™ ideal for industrial equipment power supplies that require logging as a safeguard against failures.

Other uses for logs include estimating the lifespan of a power supply based on operating time and temperature fluctuations well as detecting component degradation over time, enabling replacement before failure occurs. This is especially beneficial in applications like servers, where prolonged power outages are unacceptable.

Issue ③ Lineup/Derivative Development and Parts Inventory Management

When developing a new power supply series or custom products, traditional analog control requires changing the control IC and peripheral components, followed by extensive re-tuning, which is time-consuming and costly.

Using LogiCoA™, series development can be accomplished with minimal circuit modifications by simply adjusting parameters such as the output voltage, startup/shutdown voltages, and overcurrent, requiring only minor component changes. In addition, customizations like ON/OFF control of the RC (Remote Control) terminal and polarity changes can be easily implemented through parameter changes. The startup timing sequence of external devices other than the power supply can also be controlled via software.

Moreover, since a single MCU can support multiple topologies, there is no need to maintain separate IC inventories, simplifying both management and design. Going forward, ROHM will continue to release sample programs for different power topologies.

LogiCoA™ Power Supply Solution Technologies

LogiCoA™ MCUs

LogiCoA™ MCUs integrate an original 16-bit RSC CPU core along with a comprehensive set of analog circuits, including comparators, programmable gain amplifiers, 12-bit A/D converters, 8-bit D/A converters, and PWM circuits operating at 64MHz resolution. This makes them ideal for switching power supply control across a variety of power topologies.

At the same time, ROHM's unique event-driven control allows the built-in timer and comparator to be set according to the PWM switching timing. LogiCoA™ power solutions also do not require high-speed CPUs, reducing power consumption, while the optimized peripheral configuration for power management achieves low costs comparable to analog controllers.

Power Supply Control OS (RMOS) and Application Software

Controlling a switching power supply with an MCU requires extensive software expertise. What's more, implementing advanced, multifunctional control of switching power supplies necessitates the development of complex, large-scale programs. To simplify this process, ROHM provides the RMOS operating system for switching power supply control MCUs.

RMOS includes state transition modules that consider power control sequencing, eliminating the need to develop detailed control software. Moreover, communication and log control are managed as background modules, ensuring they do not interfere with power control operations.

RMOS significantly reduces programming complexity compared to other languages. ROHM supports power system design by providing RMOS along with application software tailored to each power topology.

Until now, controlling two different power topologies simultaneously, such as State Transition Module 1 (PFC) and State Transition Module 2 (DC-DC), required either separate control ICs or a dedicated IC. However, with LogiCoA™, a single MCU can manage both topologies, significantly reducing mounting area and overall costs.

Reference Designs

LogiCoA™ solutions utilizing LogiCoA™ MCUs provide an optimized environment for seamlessly controlling various power supply topologies. This enables the design of innovative switching power supplies that incorporate advanced digital functions while maintaining low power consumption equivalent to analog control.

Summary

ROHM hybrid analog-digital control LogiCoA™ power supplies are innovative solutions that overcome the challenges of conventional switching power supplies, achieving exceptional functionality along with low cost and power consumption while facilitating implementation. In addition to LogiCoA™ MCUs, ROHM offers a comprehensive range of components that support various power topologies, including power devices such as MOSFETs, comparators, shunt resistors, and diodes.

LogiCoA™ power solutions unlock new possibilities for small to medium power supply systems that were previously unattainable with conventional analog or digital control. This enables adoption by a broad range of power supply manufacturers for industrial robots, semiconductor manufacturing equipment, and gaming devices, as well as general industrial and consumer electronics.

Looking ahead, ROHM plans to release multi-PIN versions and LogiCoA™ MCUs compatible with LLC power supplies, expanding support for more complex power topologies. We remain committed to advancing LogiCoA™ power supply solutions to accommodate increasingly diverse power supply designs, contributing to a sustainable society by making the power supply block – one of the primary sources of power loss in applications – more energy-efficient and compact.