Power Density Roundup: New Assets in a Power Engineer’s ToolboxNovember 23, 2020 by Steve Arar
Power manufacturers are increasingly drilling down on power density as a priority. Here are a few recent updates around the industry.
While it's always nice to reduce the size of any electronic equipment, there are certain size-constrained applications that make board real estate an essential consideration. For example, in fitness-related wearables and hearables (wireless earbuds), space is at a premium. In such applications, the miniaturization of power solutions is of paramount importance and can largely affect the user experience.
Another application area in which the size of the power solution is crucial is the realm of IT and networking. With data-intensive applications such as cloud computing, artificial intelligence, 5G, and high-speed networking, massive computational power is a must.
In these cases, the designer has to miniaturize the power supply as much as possible to free up space for the computing horsepower. These examples are only some of the application areas where increasing power density can significantly improve existing systems or even enable new markets.
The following figure shows how the size of 6-A to 10-A power modules has shrunk over years.
Decreasing size of 6-A to 10-A power modules. Image courtesy of Texas Instruments
Reducing the Size of Passive Components
One of the keys to shrinking the size of a power module is cutting down the size of passive components, such as inductors, that are used for energy conversion. This can be achieved by increasing the switching frequency of a converter.
A switching converter uses passive components to store and release energy in every switching cycle. As we increase the switching frequency, a smaller amount of energy needs to be processed in each cycle and thus, we can employ smaller passive components.
However, with a higher switching frequency, some loss components referred to as switching losses increase. This can be intuitively understood by noting that with a higher switching frequency, the parasitic capacitances of the circuit needs to be charged and discharged at a higher rate. And, hence, more power will be consumed.
Another switching loss component that increases with frequency is related to the reverse-recovery phenomenon discussed in a previous article. To reduce the switching losses, we need to improve the semiconductor technology to have higher performance switches.
This can be achieved by either improving the existing technologies or working on more modern power process technologies such as GaN devices.
Thermal Performance of the Package Is Important
As discussed above, a higher switching frequency allows us to use smaller passive components and improve power density. However, this improvement comes at the cost of increased switching losses and consequently, a rise in the generated heat. Therefore, we’ll have a smaller module that generates a relatively larger amount of heat.
It turns out that it is more challenging to get the heat out of a smaller module. This is illustrated by the following figure that gives the package RΘJA (junction-to-ambient thermal resistance) versus the die area.
RΘJA vs. die area. Image courtesy of Texas Instruments
The above figure suggests that as the package size, die size, and overall power density increase, the thermal resistance goes up and innovative packaging solutions are required to efficiently transfer the generated heat to the surrounding environment. The better the package is at getting the heat out, the more power losses we can afford without experiencing unreasonable temperature rises.
Now that we are more familiar with the challenges of improving the power density, let’s take a look at three recently-announced products that aim to offer a higher power density.
Maxim Integrated's SIMO PMIC
The MAX77655 is a single-inductor multiple-output (SIMO) power management IC (PMIC) that offers four regulated outputs with a programmable output voltage in the range of 0.5 V to 4 V. The company claims that the new device enables 85 percent higher power density and can provide up to 700 mA total current from 17 mm2 PCB space.
But how can a SIMO improve the power density? A SIMO attempts to shrink the size of the power module by sharing a single inductor between different switching regulators as depicted below.
Block diagram of a SIMO architecture. Image courtesy of Maxim Integrated
This is in contrast to the traditional design where each switching regulator needs a separate inductor.
The MAX77655 targets applications, such as wearables, internet of things (IoT) sensor nodes, and health monitors, where the designer needs to miniaturize the power solution to free up space for the computing, memory, and sensor resources.
The new device enables extended battery life by providing an efficiency of 90 percent during moderate to heavy load conditions and a quiescent current of 6.9μA during light load conditions.
ABB’s DC-DC Converters
While the MAX77655 is designed for low-power wearables, ABB’s DJT090 is a 90-A DC-DC converter that aims at high-current applications such as high-speed switches and routers, artificial intelligence processors, and high-current FPGA-based processors.
The DJT090 offers a high power density of 178-A/in2. Placing up to 8 units in parallel enables a maximum output current of 720 A. A wide input voltage range of 7 V to 14.4 V is supported and the programmable output is a precisely regulated voltage in the range of 0.5 V to 2 V.
Silicon Labs’ Isolated Gate Drivers
Silicon Labs has also expressed a goal for power density with its recently-announced isolated gate drivers, the Si823Hx/825xx. These devices are designed to provide faster and safer switching with low latency (a maximum propagation delay of 30 ns) and high noise immunity.
The new gate drivers target power supplies for data centers, micro inverters for solar power, traction inverters for the automotive market, and industrial power supplies.
The Si823Hx/Si825xx are offered in several different package options to meet the space requirements of today’s compact power modules. These compact drivers are available in an 8-pin package versus comparable 16-pin package alternatives. This reduces the system size and allows us to place the driver close to the power transistor.
Besides, the new gate drivers provide symmetric 4 A sink/source capabilities. Compared to the previous generation drivers, the source current is almost doubled, which helps to reduce switching losses.
Packing a Punch in a Small Package
Power electronics may be one of the most crucial areas to focus on power density and system size. As Moore's law nears its end, it's likely we'll continue to see releases from big-name manufacturers that emphasize package size and the power that can fit therein.