Modular PoL power is becoming more accepted as a way to upply the power needs of devices such as ASICs, FPGAs, DSPs, microprocessors, and communications ICs
BY HENRY LEE
Murata Power Solutions, Mansfield, MA
http://www.murata-ps.com
As the semiconductor industry continues to move to smaller geometries, the demand for lower-voltage power converters increases correspondingly. Linked to this is a growing trend in both the data communications and industrial markets toward using a distributed-power architecture that employs an ac-to-12-Vdc power supply with one or more outputs, or isolated brick-type converters to distribute 5- or 12-V bus voltages.
The shift in power
The use of PoL modules has grown steadily over the past several years as more suppliers can now offer industry-standard products that meet customers’ power requirements at competitive prices.
Fig. 1. The Murata Power Solutions Okami OKL PoL dc/dcDC/DC power converter.
There is more behind the transition from discrete to modular PoL power than just the increase in choice and availability. Today, the ratio of analog to digital engineering know-how within most companies designing and manufacturing electronic equipment is heavily weighted toward digital, even to the point where smaller businesses have no in-house power-engineering specialists.
This happened because digital design has become the driving force behind the delivery of functionality in end products, and power generally plays the supporting role. The growing availability of modular power has helped make the outsourcing of power design possible, and has seen a shift in power knowledge and capability from OEM customers to power specialist suppliers, such as Murata Power Solutions.
Benefits of discrete PoL
In order to maximize ease of implementation and offset sometimes limited power engineering knowledge within the customer’s business, suppliers of the primary components within a discrete PoL power solution typically offer a schematic of the complete PoL circuit and a bill of materials (BOM). This is, of course, a great help to the customer when acquiring the various parts and implementing the design on a PCB.
Until recently the total cost of the components needed to achieve a discrete PoL solution was often less than that of a finished module. However, PoL module prices have become very competitive over the past few years. In addition to the board space savings they can bring, PoL modules can now be on a par or even lower cost when looking at a straight BOM cost comparison to discrete solutions.
Flexibility and ease of use
Specifying a PoL power module is now as simple as the placement of an industry-standard modular pad layout; customers need only provide the appropriate physical space and interconnects on their PCB. For a discrete approach the scenario is far more complex, as the placement of the multiple components required can be challenging depending on the size and shape of the space available on the board. In many cases a discrete approach requires the provision of more board area than a PoL module. This presents obvious issues for designers who are tasked with producing smaller equipment designs leaving less room for the implementation of a power solution.
Power requirements can often change late in the system design. With a discrete design, the system board may need to be redesigned to accommodate an increase (or decrease) in system power requirements. With a PoL module solution, multiple power levels are often available within the same package outline and pinout, giving system designers the flexibility to easily accommodate such changes with a simple change of the supplier part number on the BOM as opposed to having to respin their PCB.
In high-density circuits, where digital and analog devices are often in close proximity, the issues of EMI/RFI and thermal management must also be carefully addressed. When implementing a discrete solution, these can be time consuming and problematic to overcome with the challenge and the risk falling upon the equipment designer. With a PoL module, great consideration has been paid to the design, layout, and construction of the module in order to minimize the effects of EMI/RFI on nearby components.
Standard PoL solutions
In the isolated and non-isolated PoL power sector, the prevailing standard is the Distributed-power Open Standards Alliance (DOSA). DOSA was established by leading dc/dc converter manufacturers to ensure future product compatibility and standardization within what was becoming an increasingly fragmented power converter market. The goal of the alliance is to establish standards over a broad range of power converter form factors, footprints, feature sets, and functionality to help drive product development and facilitate alternate product sources.
DOSA defines certain criteria that make second sourcing easily achievable while still giving a fast-moving sector of the electronics market the freedom to evolve and meet the changing needs of the end applications.
New-generation PoL
Some examples of useful features seen on the latest generation modules include wide range input voltages and programmable single output voltages that make selection and implementation into a customer application more straightforward. Efficiency levels, often in the region of 93%, plus high power densities that allow designers to implement a PoL solution in a remarkably small area with excellent thermal derating performance, add to the appeal of a PoL module.
Additionally, as the majority of components become available in surface mount formats, it is advantageous for equipment designers to either eliminate through-hole components from their PCB designs or keep their use to a minimum. This enables the number of secondary PCB assembly processes to be kept to a minimum. In line with this, the latest PoL power modules are very often available in SMT as well as more traditional formats such as single-inline packages (SIP). In a further evolution of the SMT format, several of Murata Power Solutions’ Okami PoL dc/dc converters use an inspectable land grid array (iLGA) package (see Fig. 2 ).
Fig. 2. Underside view of the Okami OKL PoL dc/dc converter showing iLGA cutouts for easy access, and visual inspection as well as test probe access to all pads.
The conventional LGA interconnect package provides space savings and an excellent conduction path from the PoL module to the larger heat dissipating copper areas of the host PCB. However, they prevent easy visual inspection of the solder connection between module and PCB. To date, the only real way to overcome this was by expensive X-ray inspection methods or by destructive cross-sectioning to allow inspection of the solder joint. The iLGA package features small plated cutouts (castellations) that allow easy access for visual inspection as well as test probe access to all pads. ■
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