Power supplies are required for all electronic products: mobile phones, home appliances, automotive systems, and everything else. In serving this vast application area, Renesas has steadily developed solutions for improving performance in response to requests for chips that can make power supplies more efficient, stable and accurate. We've had particularly noteworthy success in developing semiconductor devices such as power-factor correction (PFC) ICs and low-voltage MOSFETs that reduce power losses.

Power supplies are essential system elements that convert the input power to the voltage(s) and current(s) required by all the various components in the electronic circuitry. Without the proper power supply, the system will not operate properly and may even fail. The input power is typically 100V or 200V AC from the mains, or a DC voltage from a battery. Generally, if the input power is AC, it's converted to a lower AC voltage by a transformer, then rectified and filtered to produce a DC voltage, and ― if necessary ― passed through a voltage conversion circuit (DC/DC converter) to obtain the DC voltage level(s) required in the embedded system. If the input voltage is supplied from a battery, a DC/DC converter is used to produce the DC voltage level(s) required by the various internal circuits.

In physical terms, a power supply is a function for converting energy from one form to another. Ideally, it should have no losses; in other words, it should have a conversion efficiency of 100%. This level of performance cannot be achieved in practice, but it can be approached. Ongoing improvements in design techniques and circuit components aim at enabling power supplies to achieve levels of efficiency ever closer to the ultimate goal of zero losses. Moreover, they also aim at delivering very high levels of reliability.

Across the vast span of power-supply applications, the detailed design requirements are, of course, necessarily diverse and depend on the specifics of the application. Thus, Renesas and other semiconductor manufacturers must offer power supply designs and component solutions that are optimized for customer specifications ― an increasing proportion of which specify greater efficiency in response to "green" initiatives. There is constant pressure to cut the power consumed by all types of electronics.

Renesas has long offered a very successful line of semiconductor solutions for power supplies, and we are steadily researching and developing better discrete semiconductors and ICs for this broad application area. In particular, working closely with our customers, we have honed our design skills and accumulated ― by design analysis as well as by a repeated trial-and-error approach ― a wealth of proprietary analog expertise. We incorporate this IP into solutions for powering electronic systems reliably and efficiently (see Figure 1).

Four application areas are the main focus of our development efforts for power-supply chips:

For the first three of these application areas, we have placed particular R&D emphasis on power-factor correction (PFC) ICs and low-voltage MOSFETs. Our success is evidenced by recent product introductions.

The flagship Renesas power-supply IC is the newly developed R2A20112, a PFC solution for power supplies in flat-panel TVs and flat-panel displays (FPDs). This device cuts wasted power and reduces high-frequency harmonic noise by correcting the phase and waveform of the AC power input. That is, the PFC IC ― in conjunction with the AC/DC converter ― changes the commercial AC mains voltage to the accurate and stable DC voltage needed by the internal supply-voltage distribution system.

Different control modes can be used for the PFC IC, all of which involve the use of a MOSFET switch and inductor. For situations in which the size of the power supply must be minimized, critical-mode control is recommended. With this control method and using interleaved operation, the R2A20112 provides high efficiency and also reduces the level of harmonic noise. More details are contained in the sidebar, "Critical-mode Interleaved PFC IC Features High Efficiency, Low Noise, Small Size, And Slim Profile."

One of the popular power-supply ICs that Renesas provides to manufacturers of digital cameras is the R2A20010 DC/DC converter IC. The device generates power for DSC circuits using the input voltage from a single-cell lithium-ion secondary battery or two dry cells. Because the DC/DC converter has eight output voltage channels, it can produce all of the different voltages required by the various electronic circuits in the camera. Of the eight outputs, five have internal MOSFETs. This level of integration, together with the R2A20010's use of synchronous rectification, helps reduce the external component count, thereby saving space and cost. Our ongoing efforts to increase chip integration in this and other types of power supply ICs aim to further increase efficiency, implement greater miniaturization, and facilitate additional reductions in system costs.

For notebook PCs, Renesas has developed the R2J24010, a system-in-package (SiP) device for portable computers with battery packs consisting of three or four lithium-ion cells. In a single package, this product combines an M37512 emulator MCU from our 740 family with the analog IP of an R2S20020 lithium-ion battery-protection IC. Besides implementing the battery-protection function, the R2J24010 very precisely manages the power remaining in the battery. Advantages of this SiP include a significant reduction in mounting footprint and wiring simplifications on the circuit board.

Low-voltage power MOSFETs are important power-supply components into which Renesas incorporates vital analog technologies. They're part of our line of general-purpose discrete semiconductors that also includes medium-voltage power MOSFETs, insulated-gate bipolar transistors (IGBTs), triacs and thyristors. In conjunction with our microcomputer and system solution businesses, these discrete semiconductors serve many different applications. For example, our IGBTs are the most world's top choices for camera strobes.

Renesas low-voltage power MOSFETs for power-supply applications are mainly used in DC/DC converters that operate using synchronous rectification. Two types of MOSFETs are needed for a converter design: a "high-side MOSFET" located on the supply side, and a "low-side MOSFET" located on the earth (ground) side. These MOSFETs are switched on and off, in turn, controlled in a way that ensures that the converter delivers the required output voltage and current.

The efficiency of a DC/DC converter is strongly influenced by the losses in the high-side and low-side MOSFETs. In general, to minimize those losses, the gate-charge (Qg) of the high-side MOSFET must be reduced, while the on-resistance (Ron) of the low-side MOSFET must be made as small as possible. However, differences in application requirements mandate the use of different components. For example, the best low-voltage power MOSFETs for DC/DC converters for notebook PCs are different from the best design choices for converters for desktop PCs and servers.

The latest low-voltage Renesas power MOSFETs for PC power supplies benefit from many improvements made in previous generations (see Figure 2). As a result, the devices achieve losses 30% lower than previous models because they combine low capacitance, fast switching speeds, and low on-resistance characteristics. The mainstays of the power-MOSFET product range are the tenth-generation "Jet" series (development code name) devices for DC/DC converters, and a second-generation DrMOS (Integrated Driver-MOSFET) power module for Intel's "Voltage Regulator-Down" (VRD) power-supply voltage control technology for the microprocessors in high-end PCs and servers.

An indicator of the overall performance of power MOSFETs for DC/DC converters is the figure-of-merit (FOM) index, which is based on the value of Qg x Ron. The smaller the FOM, the better. Whereas our ninth-generation MOSFETs (code name: "Speed") have an FOM index of 97mΩnC, the FOM of the tenth-generation Jet devices has been has been reduced to 78mΩnC, a 20% improvement in performance. In terms of both Ron and Qg, the values for the "Jet" MOSFETs are 30% lower than those for the "Speed" components.

The improved second-generation DrMOS power module uses system-in-package (SiP) technology to combine a gate driver circuit and two power MOSFETs (a high-side device and a low-side device) in a single package. The module delivers both a faster switching frequency and improved efficiency compared to our first-generation product by using a Schottky barrier diode inside the low-side power MOSFET, instead of the pn-junction diode previously used.

For all PCs and servers, the industry faces a challenge in supplying MOSFETs suitable for next-generation power supplies. That's because the operating supply voltage used by circuitry drops in steps due to issues of physics that arise as the advanced semiconductor processes used to build the system chips get smaller. In turn, proportionately larger supply currents are needed in order to obtain the requisite total input power. For instance, a computer system that that dissipates 100W and runs from a 5V supply needs a total current of 20A, whereas a 100W system that runs on 2V needs 50A. Low voltages accompanied by such huge increases in current are difficult combinations for power supplies to deliver. Fortunately, Renesas has the analog technology and semiconductor manufacturing expertise needed to meet this design challenge.

Organizationally, we have bolstered the importance and visibility of the Renesas solutions for power-supply applications ― PFC ICs, low-power MOSFETs, and all the others ― by moving them into our general-purpose product business, alongside microcomputers and so on. The strengthened organization can more quickly supply optimum power supply solutions for all sorts of different customer requirements.

We are working to increase Renesas' share-of-market not only for the low-voltage MOSFETs for power supplies previously described, but also for the power MOSFETs we offer for automotive applications. Our recently introduced automotive power MOSFETs provide more sophisticated operation with twice the current rating of previous models through the use of ultra-low on resistance and package technologies suitable for use with high-output electric motors. Figure 2 shows the roadmap for these product lines. More details are discussed in the Special Feature, Part 4 story, "Comprehensive Performance Is Built into Automotive MSIGs and Power Devices Step-by-step, from Chip Design to Device Manufacture to Component Mounting."

Two of the operating modes for power-factor correction ICs are continuous-current mode and critical mode. Continuous-current mode requires a complex design but is suitable for high power levels. Critical mode provides excellent efficiency and is easy to miniaturize.

The newly developed, space-saving R2A20112 PFC IC is small (10.0mm x 5.5mm) and thin (2.2mm). In critical-mode operation, it uses interleaved operation, whereby two MOSFETS are switched on and off, in turn, to minimize the current flowing through the inductor. As a result, small-sized filters, inductors, and capacitors can be used. Figure 3 shows a typical design, and the photographs show waveforms at two levels of output power, 100W and 400W.

Besides reducing ripple current and achieving high efficiency, the R2A20112 generates lower levels of radiated and conducted noise.