Consumers - A test for power converters
25 July 2008
Enhancements to point-of-load regulation may not be the first thing on a designer’s mind when it comes to developing next-generation consumer applications
However, International Rectifier argues that developments in integrated POL devices that enhance the flexibility of consumer product design, without incurring cost penalties, can lead to benefits from a commercial and technical perspective.
Consumer product design is dominated by two factors; cost and features. Design improvements that impose higher costs can usually only be justified if they deliver a benefit that is visible to the end user. It is
more difficult to make a case for improving the power infrastructure, (for example to increase efficiency or ease design pressures), than to upgrade the features of products such as gaming equipment or set top boxes.
Market insistence on price parity between conventional lighting ballasts and electronic ballasts, which deliver higher performance, greater efficiency, easier design and faster time to market, provides one example of how the purchase price remains the top priority for consumers.
However, developers must continue delivering updated products at a fast rate in line with today’s consumer
expectations, while achieving energy efficiency improvements to satisfy green initiatives. To meet these
objectives, a persuasive case must be made to improve power conversion in highly price-sensitive products.
Discrete designs Currently, cost pressures tend to drive many designers toward a discrete solution for local, or POL, power conversion in consumer products such as game terminals, graphics cards and digital TV receivers. In addition to enabling a lower cost compared to most monolithic converters, a discrete product also provides some flexibility for designers to re-use a design throughout a range of products by
selecting MOSFETs of a different rating.
Figure 1 illustrates this approach. The synchronous rectifier provides POL regulation and comprises a control IC with two SO-8 MOSFETs plus associated external passive components. A typical total footprint
for this solution is around 100mm2.
Some disadvantages of implementing a discrete solution include greater consumption of board space, difficulty in implementing voltage sequencing, (where required), lower reliability compared to an integrated solution, and a generally more difficult design challenge. Also, with several suppliers providing components for a single functional block, responsibilities can be more difficult to assign in the event that problems are encountered.
Despite these potential drawbacks, extreme cost pressures in consumerproduct markets can force designers to continue building converters similar to the type illustrated in figure 1. The technical benefits of conventional monolithic POL converters are not sufficient to justify their adoption.
Cost-neutral integration
A new converter architecture that enables a single component solution at the same overall price as a discrete implementation offers product developers a cost-neutral way to reduce design risks, shorten time to
market, increase reliability and improve operating efficiency.
By combining synchronous buck control IC technology with a half-bridge output comprising HEXFET trench MOSFETs in a single package, International Rectifier's SupIRBuck POL voltage regulators allow designers to maintain the same total solution cost compared to a discrete converter. This approach also overcomes
some of the technical limitations of conventional POL converters while delivering the miniaturisation advantages inherent in a monolithic solution.
The wide input voltage range from 2.5V to 14V allows single-stage power conversion, which allows designers to eliminate the conventional intermediate conversion before the POL device. This is vitally important in minimising the overall bill-of-materials cost to implement the power infrastructure for a cost-sensitive consumer device. An additional technical benefit is seen in increased efficiency compared to typical distributed power architectures using intermediate conversion. The overall efficiency is higher since the combined losses of two powerconversion stages are replaced by those of a single device capable of achieving around 90 per cent efficiency; even at high input voltages. If system constraints require an input voltage higher than 14V to be used, the upper limit of acceptable input voltage can be increased to 21V by applying a second Vcc bias voltage between 4.5V and 14V. This may already be available if the system has a
5V rail.
A total of nine modules, spanning current ratings from 4A to 14A, share a 5mm x 6mm Power QFN outline and have common pin-outs to combine the benefits of a small footprint with scalability and flexibility. Converters can be easily scaled from one current rating to another without changing the PCB layout, and designers can copy and paste their layout to reduce risk and shorten time to market. In contrast, traditional
monolithic or co-pack solutions feature different footprints for each current level, which requires changes to the board layout if a higher output current is required to support higher performance or increased functionality, or if the rating is to be reduced to achieve a lower cost configuration. Implementing board-level design changes increases cost, adds to the project duration, and increases risk.
In addition, the Power QFN package has a 0.9mm profile and can be mounted on the back of the PCB if necessary, to enable further space savings. When combined with the reductions in board space achievable
thanks to single-stage power conversion, this lower profile makes the devices ideally suited for space constrained, high density applications.
As an integrated product, the SupIRBuck regulator saves designers from tackling the complexities of optimising the layout and placement of the power stage portion of the circuit. EMI problems caused by sources such as parasitic board-trace inductances are also avoided. Integrated protection circuitry helps to minimise the overall footprint, including output over-current protection function implemented by sensing the voltage developed across the onresistance of the synchronous rectifier MOSFET. This method enhances the
converter’s efficiency and reduces cost by eliminating a current sense resistor.
Optimised for consumer designs
For consumer applications, six models within the SupIRBuck family are configured with features optimised for highly cost-sensitive designs. The IR380x variants include the standard SupIRBuck features such as prebias start up, fixed switching frequency, hiccup current limit, thermal shutdown, output voltage range of 0.6V to 12V, a 0.6V voltage reference accurate to ±1.5 per cent, and precise output voltage regulation.
However, where other members of the family provide additional options, such as a programmable Power-Good output and tracking capability for powering DDR memory in data-centre applications, the IR380x variants save cost by eliminating these features. Three of the available regulators are optimised for 600kHz switching frequency, and provide 4A, 7A or 12A output-current ratings. In addition, three further devices are optimised for 300kHz switching frequency. This enables a 2A increase in maximum output current, thereby delivering 6A, 9A and 14A regulators in addition to the standard output ratings.
Figure 3 shows a converter of equivalent output current and voltage rating to the discrete implementation shown in figure 1, built using a single IR380x SupIRBuck converter and requiring minimal external components. Compared to figure 1, which occupies 100mm2, the integrated regulator occupies 30mm2; thereby saving 70 per cent board space while also delivering timeto- market, scalability, efficiency, quality and reliability improvements for an equivalent cost.
When compared to conventional monolithic POL converters, IR’s SupIRBuck is typically 35 per cent smaller, thanks to a wide input voltage range and thermally enhanced Power QFN package capable of sustaining high continuous current without exceeding safe junction-temperature limits.
The time-to-market, size and cost benefits of scalable, single-stage converters mean that designers of consumer applications now have access to technologies that deliver a number of benefits without incurring cost penalties over more traditional discrete approaches. Specifically, new and emerging generations of high-efficiency co-packaged regulators offering a wide input voltage range allow consumer product brands to cost-effectively meet multiple requirements dictated by consumer expectation, economic pressures, and environmental commitments.
PARVIZ PARTO is senior systems/ applications manager, enterprise business unit senior systems / applications manager GORAN STOJCIC is executive director, IR enterprise power applications and technical marketing
Contact Details and Archive...
Related Articles...
Most Viewed Articles...