Future Electronics – DC/DC Converters: The DRAM of Power Products?

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By: J. David DeLeonardo, Regional Analog & Power Specialist, Future Electronics

After a few blissful decades of relatively stable margins, in recent years, analog and power products have finally come under the same pressures that have driven down prices and margins for digital products. In this paper, we will take a look at the general trends that are driving these declines and are common to nearly all classes of analog and power products.

Definitions and Benchmarks
Let’s get started with some definitions of the power products we will be considering along with their typical performance characteristics.

Power Stages: These products contain the FETs and the requisite drivers needed to implement a single phase of a synchronous buck topology (see Figure 1). A standardized product class of power stages is referred to as “DrMOS” whose name is derived from a shorthand of “Drivers + MOSFETs.” Some recently introduced power stages include the passives (inductor and some output capacitance) required to implement a single phase of a synchronous buck converter, MINUS the controller. Typically, these products are aimed at 12V down conversion applications with current ratings from 30A to 80A. (Some parts range up to 24V/5A.)

Figure 1: While “sole source” power stages can have unique pin outs, footprints and functionalities, the DrMOS products (generally) share a standardized pin out, footprint and function set. Figure 1 shows a typical application where a controller is driving a power stage to implement a single phase synchronous buck DC/DC conversion stage. Feedback from the output back to the controller has not been shown for sake of clarity.

Figure 1: While “sole source” power stages can have unique pin outs, footprints and functionalities, the DrMOS products (generally) share a standardized pin out, footprint and function set. Figure 1 shows a typical application where a controller is driving a power stage to implement a single phase synchronous buck DC/DC conversion stage. Feedback from the output back to the controller has not been shown for sake of clarity.

Controllers: These products contain the sense and control circuitry required for implementing a single or multi-phase switch-mode power conversion stage absent the power switches and associated passives (see Figure 2). Some controllers also contain the drivers required to switch the external power FETs for lower current applications. Input voltages typically range from 3V to 70V with some newer product ranging up to 100V. Output current is determined by the particular power FETs or power stage(s) used. Controllers can range from a simple single phase/single control loop device to multi-phase/multi-loop parts used to support high-end processors/ASICs/FPGAs.

Regulators: These products contain a controller circuit PLUS the requisite power switches and their associated drivers. Input voltages range from 3V to 70V with some newer products ranging up to 100V. Output currents are typically in the range of tens of milliamps to 10A. These are typically single or dual output devices, but recent parts also provide LDO outputs and/ or triple switcher outputs. Of course, highly specialized PMICs (Power Management ICs) have many switchers and LDOs (and other functions), but these are outside the scope of this paper (see Figure 2).

Figure 2: DC/DC Product Definition Summary

Figure 2: DC/DC Product Definition Summary

Modules: These contain a controller, drivers, power switches and the passives (inductor and output caps) required to implement a power conversion stage. The amount of additional EXTERNAL output capacitance that will be needed is application dependent. These can be open frame or potted, isolated or not, and through-hole or SMT. Input voltages typically range from 5V to 75V with currents ranging from about 400mA to 40A (see Figure 2).

Bricks: This is a term that was originally used to refer to a specialized class of isolated DC/DC power supplies that generally accepted a nominal 48VDC input (36VDC to 72VDC) and produced one or more isolated and down-converted DC outputs. They had a standardized form factor including their power, control and monitoring pins or pads. Size categories ranged from “full brick” to “1/8 brick” (recently down to 1/32 size). However, over the past decade, this term has been considerably broadened to include a wider input voltage range and alternative form factors. One constant that remains is that the output(s) are still isolated from the input.

Picture 1 shows a typical brick that implements integrated magnetics to facilitate the small form factor. Integrated magnetics replace the wire coils of the transformers with circular traces on multiple layers of the PCB. The core is then assembled around them in such a way as to complete the magnetic circuit. Due to the high number of wide circuit “turns” required, the PCB can end up being quite thick as seen in Picture 2.

Picture 1 shows a typical brick that implements integrated magnetics to facilitate the small form factor. Integrated magnetics replace the wire coils of the transformers with circular traces on multiple layers of the PCB. The core is then assembled around them in such a way as to complete the magnetic circuit. Due to the high number of wide circuit “turns” required, the PCB can end up being quite thick as seen in Picture 2.

High-Level Trends in Power and Analog Products
Trends in Pricing and IP: With “expiring” IP and accelerating investment in analog processes and products, when prices are taken on a normalized basis for a given set of performance parameters, price erosion for nearly all analog and power products is actually accelerating. For example, in 2014, sub-24V DC/DC regulators saw a 15% decline in overall ASPs. Thus, a simple 14V/3A sync buck regulator is now available for under $0.50 in high volumes. In the module space, the metric “cents/amps” is used to characterize the prices found in various products classes. Thus, for example, in the sub-6V range, prices have fallen from $0.85/A in large quantities just 2 years ago to below $0.50/A today.

This trend is happening so quickly, that it has resulted in a market condition where a parametric search can yield functionally identical parts that differ in price by a factor of 2x or even 4x. As previously proprietary IP passes into the public domain, established vendors are responding by pushing to higher voltages where there are higher barriers to entry, resulting in fewer competitors and higher margins. Additionally, because customers increasingly want to avoid “sole source” components, interoperability alliances are emerging among the module and controller vendors. Also, sockets are being “up-converted” such that applications that once would have used controllers now use regulators and those that once used on regulators often now use modules. Finally, the “inflection point” where applications transitioned from FETs to power stages has risen from about 20A per phase 5 years ago to roughly 30A per phase today.

Trends in Process and Materials: In the last few years, power FETs and diodes have become available in alternative materials including SiC and GaN. These materials remain substantially more expensive than the more mature Silicon devices, but the price premium between them is rapidly declining. For those applications that are able to take advantage of their performance advantages, devices built with these new materials can be used to increase the overall system performance and lower the system cost. Given the pervasive push for higher energy efficiency in nearly all applications and the increasing importance of applications that require high voltage/ high current devices, devices implemented in these materials will continue to displace traditional Silicon devices. Presently, these materials have only been used in discretes and in power stages. No controllers or (monolithic) regulators are yet made in these materials as they are very difficult to process. Modules and bricks are only recently using these advanced process materials such as SiC and GaN. However, as the price/performance premium for these materials continues to decline, this migration will accelerate due to the inherent performance advantage of these materials in those applications that favor modules/bricks.

Trends in Packaging
Power Stages: Due to advances in process and packaging, power stages now enable per phase currents from 30A to 90A. Additionally, passives are being combined with drivers and discrete FETs to create “integrated power stages.” Beyond even this, there are a products coming out that combine multiple “integrated power stages” onto PCB carriers to create “multi-phase power stage assemblies” (see Picture 2).

Picture 2

Picture 2

Modules: Perhaps more than any other product category, modules have seen a steady advancement and proliferation in packaging technology. Table 1 shows a few of the many varieties now available.

This thermally enhanced over-molded QFN package requires no heat sink, even at full load. It allows use of standard SMT assembly equipment while facilitating easy probing of all pins.
This “land grid array” package was among the first means of producing ultra-compact DC/DC modules. Its internal PCB structure allows for quick product development without the need for a custom lead frame.
This “PFM”package accommodates wide input voltages and very high output currents while allowing the use of standard “IC mounting” techniques. The package also supports the use of very large inductors for wide input/output voltage ranges and differentials.
When the output current requirements in an application increase to where an LDO can no longer be used, this through-hole package allows “pin-for-pin” drop in replacement by a switching power supply (module).
This through-hole package allows for isolated DC/DC conversion stages with dual outputs and ample space to meet most creepage and clearance specifications.
These DFN packages (2.5 x 2.0mm and 3 x 3mm, respectively) offer exceptionally high power density with heights below 1.1mm.

Table 1

Bricks: From the original “full brick” form factor of 110 x 50 x 12mm (approximate), brick products are now available in 1/2, 1/4, 1/8, 1/16 and even 1/32 fractional size categories. These fractions represent (roughly) the fractional size of the product as compared with the original “full brick” form factor. Due to increases in process, design and packaging technology, the power density of these products is also steadily increasing with a 1/32 brick now able to deliver 30W (see Picture 3).

Trends in Integration/Digitalization
For power stages, there is a trend toward integrating such features as diode emulation, thermal monitoring and adaptive dead-time control. All these require additional digital (and analog) circuitry, but add substantial value in increased efficiency and performance. For the other product categories (controllers, regulators, and modules/bricks) there is increasing availability of “all digital” devices in both single and multi-phase configurations. There is also increasing availability of hybrid products available. These have analog control loops operating under the control of a digital “wrap” that can be configured, monitored and controlled by the application host via a digital communication port.

Considering each product category separately, for controllers, a wider range of topologies (beyond buck) are being supported in both “hybrid” and “all digital” devices including flyback, forward and sync boost. For regulators, products have been released that provide access to the internal microcontroller that is “supervising” the analog control elements. This allows the part to fill the role of a simple “application processor” or host as well as the primary power conversion device. Modules and bricks are increasingly available in both “hybrid” or “all digital” options that enable enhanced in-application monitoring and control of the power stage by the application host micro.

Picture 3

Picture 3

Trends in Relative Socket Loss
Power Stages: In lower current applications, improvements in power FETs and drive capabilities of controllers displace previously needed power stages. However, as load current requirements for very large silicon devices continues to increases, opportunities for power stages increase.

Controllers: As the current and voltage capability of regulators continues to improve, controllers lose sockets to that class of products. DC/DC controllers are being integrated into RF modules, microcontrollers and processors as well as being functionally implemented with general purpose microcontrollers. It should be noted that shortening design cycles also favor regulators vs. controllers.

Regulators: Many applications are integrating the DC/DC conversion stage(s) into the application module as in the case of Bluetooth Low Energy (BTLE) modules. Similarly, many host processors now have sufficient analog resources to allow them to “simply” implement this functionality for themselves. In applications where space is at a premium and cost must be minimized, and as modules continue to improve with regard to current/voltage capability, regulators will continue to lose sockets to modules. It should be noted that shortening design cycles also favor modules over regulators.

Module/Bricks: As their current and voltage capabilities continue to increase, modules are gaining ground in nearly all applications that value high power density or quick design turn or ease of design.

Trends in Support Tools: All power product categories have seen a rapid and extensive introduction of online design and simulation tools. These range from simulators that focus on individual FET switch performance to full system level design assistant type environments that allow a designer to quickly model a given power system in terms of input sources and output loads, select likely power conversion components and then simulate the performance of the overall system as well as each conversion stage. These tools have substantially cut the development time required for power systems and increased the degree of refinement possible, even in increasingly short design cycles.

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