Flexible Power Islands Solve Difficult Power Problems in Mobile Devices

Power system design in the age of mobile devices, and especially wearable devices, is more challenging than it has ever been.  The end users of these devices want them to continue to get smaller, lighter and cheaper, while at the same time having bigger screens and longer battery life.  These opposing goals serve as one of many challenges facing the power system designer who are driving the power system market in new directions, and demanding innovative new solutions.  Figures 1a & 1b highlight several other challenges for power systems in mobile devices.  Silego Technology is responding to these challenges by introducing a new concept of Flexible Power Islands, which breaks up the traditional architectural boundaries in mobile device power systems.  These new devices are small yet powerful components, each of which gives the designer much greater levels of flexibility than they have ever experienced in the past.

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Figure 1a: Mobile Device Power System Challenges

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Figure 1b: Mobile Device Power System Challenges

Looking back in history, the functional elements needed in a computer power system have grown over time. These functions have traditionally included various types of voltage regulation, including both linear regulation as well as switching regulation.  As these systems have grown more sophisticated, the number of voltage rails has also grown.  The more power rails required, the more likely that some control elements are needed to manage the sequencing and timing of each of the rails.  Similarly, as the number of power rails increase, it is also more likely that some level of slew rate management and/or power gating is required.  The requirements for this level of sophistication in the power system is driven by the specifications of advanced CPUs or SoCs, which have stringent requirements regarding the sequencing and ramp rates of individual voltage rails in the system.  To enhance the robustness of the system, active monitoring of the power lines can be included, which will raise flags if the power system is acting outside of pre-determined levels.  Lastly, it is also common to include real-time clocking functions in the power system.

All of the functions listed above are available in the market in discrete form.  There are both positive and negative aspects of choosing to build the power system for a mobile device in discrete form.  Chief amongst the positive aspects is the fact that there are multiple sources for all of these functions.  This is especially true for switching and linear regulators, which are available from many vendors, and in an almost infinite variety of input voltage, output voltage, power performance and noise performance.  Another advantage of using discrete components to build these power systems is the inherent flexibility to locate the components physically close to the Point Of Load (POL).  This can increase the overall system efficiency by lowering the IR drops by shortening up trace lengths, as well as make the complex board level design easier.

Despite the fact that discrete power components can provide advantages in a mobile device, they do have a few big disadvantages that hamper their wide adoption.  The most important disadvantage is the physical size required to use these components, as every device manufacturer wants to drive down the board size, to either shrink the physical size of the end device, increase the size of the battery for better life, or a combination of the two.  A second large downside in using discrete components in mobile devices is that they do not offer the multiple power saving modes usually found in more integrated solutions. 

The drive to greater levels of integration in the power systems for mobile devices lead to the introduction of Power Management ICs (PMICs).  These devices are designed with the goal to be a complete power system on a chip.  These devices include a set of resources that are meant to match the power requirements of a particular SoC or processor.  They typically include some number of channels of linear and switching regulators, as well as power sequencing functions.  They do have a distinct advantage over discrete components by offering a higher level of integration, which usually means that the board area required by the power system is substantially reduced. 

As mentioned previously, battery life is one of the most important performance characteristics for the users of mobile devices.  For this reason, manufacturers of these devices are in fierce competition with each other to offer the best battery life in their product.  The fact that this performance characteristic is so important to their customers, leads to one of the most common complaints from power designers concerning PMICs. The complaint centers around the fact that when a power designer is using a PMIC to serve as most or all of their power architecture, this does not give them much latitude to differentiate the power architecture in their device relative to their competition.  The end result is that it hard to have a solution that exhibits noticeably better battery life than other similar mobile devices.  

Silego Technology is introducing the concept of Flexible Power Islands to overcome some of the limitations that are inherent in both PMIC and discrete power implementations for mobile devices discussed above.  In particular, customers are looking for solutions that have greater levels of integration than can be achieved using discrete components, but also having more flexibility to innovate than is available in existing PMIC architectures.  One aspect of the new level of flexibility that Flexible Power Islands offer is a distributed architecture, with the goal to be able to use these “islands” of local power control near the point of load on the target board. This can reduce power trace lengths, which will yield an inherent increase to efficiency.

The Flexible Power Island device that Silego is introducing is the SLG46580, which is an outgrowth of the GreenPAK™ (GPAK) product line.  The GPAK devices are Programmable Mixed Signal Matrix components, which offer a user-configurable combination of analog and digital functions.  These devices are all physically small, with packages ranging from 1.0 mm x 1.2 mm QFNs to 2.0 x 3.0 QFNs.  All of the devices in the GPAK family are programmable, and include the ability to both configure the analog and digital logic elements, as well as define the interconnections between the different resources. The user interacts with the resources on the device in a similar manner to doing a board level design with discrete components.  The software created by Silego to facilitate development, called GPAK Designer™, has a similar interface to schematic capture board level design packages.  Figure 2 shows the GPAK Designer software graphical user interface, with the user selected interconnect lines shown in green.

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Figure 2: GreenPAK Designer Software Graphical User Interface

The new SLG46580 has all the flexibility of the other members of the GPAK family, as well as some unique features that make it particularly well suited to implement a Flexible Power Island.  This device includes four 150 mA LDOs that are programmable in their output Voltage.  These LDOs can be controlled in a variety of ways, including enable/disable, output Voltage change and low power mode enable to save power.   Figure 3 shows the block diagram for the SLG46580, showing the various analog and digital resources.  This device includes four analog comparators, that can be very useful for monitoring of voltage rails.  It also includes “Combination Function Macrocells”, which are user selectable for either a Look Up Table (LUT) function, or in some cases as a DFF,  or in other cases as a timer/counter.  A unique function included is the Asynchronous State Machine microcell (ASM), which allows the user to define a logical state machine, define the allowed state transitions, and assign the signals that will drive each of these state transitions.  This device also has a Real Time Counter function block, that includes a 15-bit pre-scaler,  a 32-bit active counter and a 32-bit digital comparator which can be used for an alarm function. Even with this wide array of useful functions, the SLG46580 comes in a tiny 2.0 x 3.0 mm QFN package, sized to fit the most space constrained board.

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Figure 3: SLG46580 Block Diagram

There are several ways that a power systems designer can benefit from adding flexible power islands to their system.  One potential use for this technology is to augment existing PMIC based power systems.  In this role, the flexible power islands can allow the designer to quickly support the ever-expanding list of features that are being demanded by end users. A good example of this is support for the latest camera technology, which happens to be an area where mobile device manufacturers are working hard now to differentiate their products.  In smaller mobile devices, (think wearables), where the number of power rails is somewhere between three to six, this technology can serve as the heart of the power system, providing power sequencing, power monitoring and linear regulation.  The SLG46580 can also control external switching regulator components, to provide all the needed function for the entire power system.

The challenges facing the power systems designer in the mobile market are severe.  The performance in the power system must continue to go up, to give the end users the features and battery life that they demand, while at the same time the board area for the power system must get smaller.  Silego developed the Flexible Power Island concept, and the SLG46580 device, to give designers a new set of options to meet these challenges.  

For Flexible Power Islandstips, techniques & design examples, register for Silego’s upcoming online webinar, which will be hosted Wednesday, June 28, 2017 at 4:30 PM PST.  Register Here to attend & receive a video recording.

Silego Technology