Power supplies that meet customer demand
Enhancing analog control with improved accuracy and logging featuresAnalog-Digital Hybrid Control Power Supply

Combining the Best of Analog and Digital Control

In power circuits, there are two types of control methods: analog topologies that use analog compensators such as error amplifiers for PWM calculations, and fully digital control power supplies that perform PWM calculations by employing digital compensators like DSPs.
Fully digital control offers a high degree of flexibility, allowing control methods and parameters to be adjusted through software. What’s more, since it does not depend on the characteristics of analog elements, margin design is unnecessary, leading to excellent long-term stability. However, to minimize delays in the loop, high-speed ADCs and high-performance CPUs/DSPs must be fully utilized, significantly increasing the cost and power consumption of the control circuit. In small power circuits typically ranging from 50W to 1kW that represent the volume zone for industrial equipment, analog control ICs have been preferred as reducing cost and power consumption has been prioritized over the benefits of digitalization.
LogiCoA™ is a new design concept that leverages the advanced functionality and efficiency of fully digital control while maintaining the low cost and power consumption of analog control (Fig. 1).

Figure 1. LogiCoA™ Fuses Analog and Digital in Power Supply Design

LogiCoA™ utilizes low-cost, low-power analog circuits for PWM control calculations while incorporating the advantages of digital technology, including functions for calibrating device variations, optimizing switching dead time, and acquiring operation logs useful for troubleshooting (Table 1). Furthermore, to help development engineers familiar with analog power design utilize digital technology without needing to focus on software design, the digital control aspects are easily implemented using our proprietary RMOS (power control OS).

Table 1 Advantages of Analog-Digital Hybrid Control

3 Benefits of Digital Control

Integrating digital control addresses common challenges faced by designers of analog control power supplies.

(1) Calibration Contributes to Component and System Miniaturization

With analog control, control operations are determined by the circuit configuration and component values, making it difficult to adjust parameters. To account for variations in component values, circuit designs often incorporate margins of several tens of percent, resulting in larger components and systems.
LogiCoA™ enables narrower margins and smaller elements through digital calibration (Fig. 2).

Figure 2. Benefit (1) Calibration Reduces Margins

(2) Enables Failure Analysis and Complaint Handling Through Operational Log Storage

With LogiCoA™, values such as output voltage during operation can be automatically saved to internal memory and retrieved for analysis at any time. Log storage and retrieval do not affect power control, allowing for accurate remote maintenance, root cause analysis during failures, claim management, and lifespan predictions due to aging degradation.

(3) Expands the Power Supply Product Range by Simply Changing Software

In analog control power systems, it is necessary to change the power control IC for each power supply topology. The leads to a diverse component inventory, increasing management burden.
LogiCoA™ can accommodate various power topologies through software, facilitating inventory management.

LogiCoA™ Hardware and Software

As illustrated in Fig. 1, LogiCoA™ designs the basic topology and analog compensator (error amplifier) tailored to each power supply, executing PWM control through an analog-digital hybrid circuit that utilizes comparators and timers. This approach is termed event-driven control, as the PWM duty is regulated for each clock by a high-resolution timer triggered by analog input, all without CPU intervention (Fig. 3). Meanwhile, the ultra-low power CPU operates in the background, managing power ON/OFF, input/output monitoring, current detection, communication control, and log acquisition according to the software schedule.

Figure 3. Event-Driven Control

To simplify the design of real-time schedule management, proprietary real-time OS RMOS was adopted for power control (Fig. 4). RMOS allows users to easily configure operations by defining the functions of each module in a template state transition diagram. In addition, sample software is available for each topology in power control applications. The operating parameters that define the characteristics of the power supply can be easily configured using an Excel-based input screen, eliminating the need to consider programming.

Figure 4. Overview of RMOS Simultaneous control of two converters with one MCU is possible

LogiCoA™ Development Environment and Evaluation Board

ROHM provides LogiCoA™ chips, development tools, and software, as well as evaluation boards for various topologies, including buck DC-DC converter and PFC + flyback converters.
The PFC + flyback converter reference board (shown in the title cut photo) integrates the LogiCoA™ chip along with the necessary external circuitry. A single LogiCoA™ chip can simultaneously run two software programs, one for PFC and the other for flyback.

LogiCoA™ is a trademark or registered trademark of ROHM Co., Ltd.