Thin and efficient power conversion solutions

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With the development of various electronic devices towards miniaturization, traditional power conversion modules also need to reduce their size and improve efficiency to meet increasingly stringent system requirements. The new charge pump architecture will be the key to achieving thin and efficient power conversion modules. This article will introduce the characteristics of the charge pump architecture and the product advantages of the new power conversion solution introduced by Murata.

The charge pump architecture enables thinning and high-efficiency implementation

The charge pump is a DC-DC converter that utilizes capacitors to store energy, allowing it to generate doubled voltages, half voltages, and invert voltages. It consists of switching devices and capacitors, operates in an open-loop control manner, and the output voltage exhibits a drooping characteristic, which decreases as the load current increases. Additionally, the charge pump does not require inductors, which are typically the largest components occupying significant PCB space in DC-DC converters. On the other hand, the charge pump enables the realization of small and thin DC-DC converters.

Because the charge pump is a topology that supplies power to the output capacitor (COUT) discretely, it takes some time to delivering power from COUT to the output load. As a result, the output ripple voltage increases. To address this issue, many capacitors or large capacitance must be installed, leading to an increase in solution size. Moreover, during the charging period of discharged capacitors, transient currents occur on the capacitors, subjecting the components to stress from these transient currents. Furthermore, charge redistribution losses (specific losses related to charge transmission between capacitors) contribute to reduced efficiency. Consequently, charge pumps have not been widely applied in extremely low-power products.

Conventional step-down converters, typically composed of input and output capacitors, high-side MOSFET, low-side MOSFET, and an inductor, are commonly used for step-down conversion. They are power electronic circuits that convert DC input into variable DC output. By adjusting the ON time of the MOSFET, it can convert the input voltage to the desired output voltage. The ON time is determined by a feedback circuit to maintain a constant output voltage, even with variations in input voltage or output current.

In terms of architecture, the behavior of charge pumps differs from conventional inductor-based step-down converters. A charge pump is a divide-by-N capacitive voltage converter, with the voltage conversion ratio depending on each product. It operates as an open-loop converter and does not possess output regulation capability. Therefore, the output voltage decreases with an increase in load current.

The inductor current is determined by the voltage, on-time of MOSFET, and inductance. To reduce ripple current, it is necessary to increase the inductance or switching frequency, resulting in an increased number of turns or increased core cross-sectional area to achieve higher inductance. In traditional inductor-based buck converters, the DC resistance (DCR) increases with an increase in the number of turns, leading to increased conduction losses. When using thicker windings to reduce losses, additional winding space is required. Thus, a larger core is needed. Due to the larger core size, downsizing the inductor of high-current step-down converters become challenging. Setting the switching frequency to a higher value for smaller size leads to increased MOSFET switching losses, resulting in decreased efficiency. Due to the limitations of inductors, achieving smaller size, low-profile, and high efficiency becomes more difficult.

On the other hand, charge pumps power through capacitors. In circuit topologies that utilize inductors or transformers for voltage conversion, magnetic components often become the bottleneck for low-profile product. As mentioned above, using thin magnetic components leads to reduced efficiency. Charge pumps enable low-profile and high efficiency because the power density of capacitors is higher than that of inductors. Therefore, employing charge pumps allows for high power density power supplies.

The charge pump is a voltage conversion solution that enables small size and high efficiency, especially in applications that require low-profile. However, its disadvantage is that the load regulation is inferior to that of a step-down converter, it is suitable as a first-stage converter in intermediate bus systems, with the output voltage regulated by point-of-load (PoL) converters as the second stage.

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A small-sized and high-efficiency voltage conversion solution employing a charge pump architecture

Murata has introduced the MYC0409-NA, a product that utilizes a charge pump architecture. This module addresses the disadvantages commonly associated with charge pumps, such as increased output ripple, larger PCB size, and transient stress on the device, by incorporating Murata's proprietary design techniques.

The MYC0409-NA operates at a fixed divide-by-four conversion ratio from input voltage to output voltage, enabling conversion from 48V to approximately 12V. It is designed to provide stable intermediate bus voltage for both 48V and 54V systems. Thanks to Murata's proprietary charge pump technology, this module achieves high efficiency and power density within a height of 2.1mm. Furthermore, Murata's technology eliminates the need for higher or heavier parts, allowing for mounted on the backside of the PCB board.

Murata's charge pump utilizes small inductors that are connected after the charge pump and can be combined with LC filters to reduce output ripple voltage. Since the voltage amplitude across the inductor is significantly smaller compared to a step-down converter, high inductance is not required. The lower number of turns and lower inductance allow for the use of inductors with small DC resistance (DCR), resulting in reduced conduction losses. Although the average input current decreases proportionally with the conversion rate, the instantaneous input current is equal to the output current through the step-down converter and is smoothed by the input capacitor. Additionally, Murata's UltraCP™ employs a two-phase configuration with a fixed duty cycle of 50%, delivering power in each cycle of the input current. This design ensures no transient current change in the input capacitors. The ripple current flowing through the input capacitors is equivalent to 1/N of the inductor current (where N is the voltage conversion ratio). As a result, fewer capacitors can be used to achieve low input ripple voltage.

As an example of the UltraCP™ series applied in small cell systems, the MYC0409-NA can be mounted after an AC/DC converter or DC/DC isolation converter to generate 12V from a 48V line. By employing the UltraCP™ series, high-efficiency and small-sized systems can be realized.

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Ultra-efficient non-isolated DC-DC converter module

The UltraCP™ MYC0409 by Murata is a non-isolated DC-DC converter module that offers ultra-high efficiency. The MYC0409 is a fully integrated module with a 48Volt divide-by-4 charge pump capacitor, capable of delivering up to 72W of power with a peak efficiency of 96.5%.

The MYC0409-NA is an ultra-thin and highly efficient integrated power solution that combines a 72W DC-DC converter with components. It occupies minimal space on the PCB backside with a thickness of less than 2.0mm. This complete power solution is suitable for systems that do not require loop compensation and only need three external components in the minimum case.

Despite its small and thin 11.5 x 9.5 x 2.0mm LGA package, this fully integrated module achieves an efficiency of up to 96.5%, reaching 95.0% efficiency at 48V input and 6A output. Murata's module features an easy-to-use pinout arrangement design that allows for a simple power layout and maximizes efficiency by minimizing routing parasitic resistance. The module has a fixed divide-by-4 conversion ratio from input voltage to output voltage, with an input voltage range of 20V to 60V, supporting 48V bus systems. It offers high power density (5.4kW/inch3), excellent thermal performance, low ripple, low electromagnetic interference, and operates in a temperature range of -40 to +105°C.

The MYC0409 module demonstrates a peak efficiency improvement of 2.5% over a 1/16 brick 70W power supply. It also exhibits lower temperature rise (50°C lower than) and reduced output ripple (75% lower). Additionally, it shows a 20dB reduction in radiated electromagnetic interference. A single MYC0409 module can save more than 80% in size and 75% in height compared to a 1/16 brick 200W power supply. When three MYC0409 modules are parallel-connected, it can achieve more than 35% size reduction and 75% height reduction compared to the 1/16 brick 200W power supply. MYC0409 is highly versatile and Murata can provide industry customers with packages that comply with the DOSA standard.

The MYC0409 modules can be connected in parallel, with up to four modules paralleled together to provide a high-power, high-efficiency solution. They feature good open-drain power outputs, overcurrent and over-temperature protection, use a compensation loop-less charge pump, and can synchronize with an external clock. They are suitable for various 48V-to-12V step-down applications such as data centers/servers, network routers, base stations, optical equipment, test equipment, and LED signage.

Murata also offers the MYBSN-P2 evaluation module, which accelerates customer product development. The MYBSN-P2 is a 1/16 brick high-efficiency non-isolated DC-DC converter module that utilizes the MYC0409. By simply applying the input voltage, the MYBSN-P2 generates a divided voltage on its output. It has a fourfold division ratio (VOUT=VIN/4), a wide input voltage range of 20V to 60V (divided by four), an efficiency of up to 96.3%, and achieves 95.0% efficiency at 48V input and 10A output, supporting outputs of up to 10A.

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Compact, low-profile, and highly efficient step-down DC-DC converter solution

Murata's FlexiBK™ PE24108 power semiconductor is a compact, low-profile, and highly efficient step-down DC-DC converter solution. It provides an output current of 10A per stage within an input voltage range of 3.0V to 3.6V. It supports a nominal 3.3V bus voltage operation for the output voltage, which can be adjusted between 0.4V and 1.0V through external feedback resistors. The solution offers a peak efficiency of 92% and output voltage regulation accuracy better than ±1% for all line and load variations.

The PE24108 features an innovative two-stage architecture, consisting of a two-phase interleaved charge pump and an interleaved buck regulator. This design achieves a significantly low profile and compact footprint, reducing the reliance on inductors for efficient solutions in small footprint and height-constrained applications.

Each phase of the PE24108 can deliver 10A of current, and up to 4 phases can be paralleled to support 40A. The output can be adjusted externally using an AVS DAC, and an external synchronization pin allows synchronization with an external clock. The PE24108's ultra-high efficiency and low ripple performance make it suitable for space-constrained and noise-sensitive applications, including low-profile load point (POL) regulators, DSP/ASIC in optical modules or FPGAs in network equipment, and core power supplies.

Conclusion

Traditional power conversion modules are typically the largest components in a system. If it is possible to reduce the volume of the power conversion module and improve the conversion efficiency, it would significantly shrink the system's overall size, improve system stability, and lower power consumption. The new UltraCP™ MYC0409 DC-DC converter module with a novel charge pump architecture introduced by Murata, along with the innovative two-stage architecture design of the FlexiBK™ PE24108 power semiconductor, would be an ideal solution for reducing the size and improving the efficiency of power conversion modules.

 

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