Tiny SIMO PMIC charges wearables 4x faster, shrinks solution size by 50%

Analog Devices, Inc. has released its MAX77659 single-inductor multiple output (SIMO) power management IC (PMIC) with an integrated switch-mode buck-boost charger that claims to charge wearables, hearables, and internet of things (IoT) devices faster and in less space than any other PMIC available today. Aimed at consumer and medical wearable devices, the SIMO PMIC delivers over four hours of play time with a ten-minute charge, delivering four times faster charging compared to other solutions, and uses a single inductor to power multiple rails, helping to shrink the total solution size.

Prior to Covid-19, people with chronic conditions or who were very sick or elderly were the only ones monitoring their vitals at home, said Karthi Gopalan, executive director, Battery Power Solutions Business Unit, Maxim Integrated, now part of Analog Devices. “With Covid-19, we saw a paradigm shift in the world of wellness with healthy people buying these gadgets.”

MAX77659 SIMO PMIC applications. Click for a larger image. (Source: Analog Devices, Inc.)

Traditional medical companies were trying to shrink their form factors, go battery powered, and make the devices more stylish while the lifestyle brands were trying to add more vital sign monitoring, so the two worlds are coming together, she said. “We saw the big lifestyle brands starting to move into the medical space and the medical folks asking for the same power solutions that the lifestyle brand folks were using.”

For wearable designers this translated into challenges around comfort and the need for smaller and sleeker form factors, higher accuracy for precision measurements, faster charging, longer battery life, and growing demand for more integrated features.

These gadgets are sometimes worn 24/7 so a thin form factor and sleek and light design become critical for comfort, Gopalan said. “Accuracy is a no-brainer because we are doing vital sign monitoring so precision measurements become very critical and more and more of our customer base is asking for over 24 hours of charge and some medical companies ask for up to five days, so the longer battery life becomes very critical and we are able to hit that with our higher efficiency power solution.”

MAX77659 application example (Source: Analog Devices, Inc.)

In addition to delivering a faster charge, the new integrated SIMO PMIC is reported to reduce the bill of materials (BOM) by 60 percent and shrink the total solution size by 50 percent. By freeing up the board real estate designers can pack in extra sensors and/or memory as well as add new features such as location tracking and vital-sign sensing.

A traditional solution (see figure below on the left) has limited sensing and a very basic CPU, but lifestyle and medical brands are asking to pack more and more sensors like the BioZ and PPG sensor, and it doesn’t stop there, Gopalan said.

Designers are also looking to add location (GPS) tracking, haptics, and AI processing because a lot of data is being generated, she said, however, “the traditional CPU doesn’t cut it and the AI processor is more power hungry, and where do you squeeze in the power management solution?

“We developed a very unique SIMO architecture with the right amount of integration like the charger, and we were able to shrink the whole power architecture in half, so all these extra sensors (see figure below on the right) can be packed into the same compact form factor,” she said.

SIMO PMIC enables more integrated features. Click for a larger image. (Source: Analog Devices, Inc.)

Higher integration

The MAX77659 SIMO PMIC integrates a switch-mode buck-boost charger and three independently programmable buck-boost regulators that all share a single inductor to minimize the total solution size, which is thanks to the SIMO architecture.

“Generally, a typical power management IC will have multiple voltage rails – stepping up/down the voltage levels, so when you have three voltage or switching rails, you need three separate inductors, and these inductors are super bulky,” she said. “With the MAX77659, the three rails only require one inductor, which has freed up extra space.”

The PMIC is not only the smallest it also has the lowest Iq [quiescent current] in the industry, which means 20% longer battery life, Gopalan said.

The three regulators extend battery life by operating at 91 percent efficiency during moderate to heavy load conditions while consuming only 5 µA of quiescent current during light load conditions. It also includes an LDO with a high PSRR for sensitive applications.

In addition, the PMIC supports autonomous headroom control, which reduces heat dissipation by minimizing the voltage drop while providing enough headroom to regulate the charging current. Together, the fast charging with autonomous headroom control improves battery life.

This translates into four hours of playtime with just a ten-minute window of charging, compared to a linear charger with one and one-half hours of playtime with a 10-minute charge, Gopalan said.

Another issue is heat. “When you push a linear charger to go into fast charging, it causes a 25°C temperature rise and a hot spot. Certain countries like Japan, which has the JEITA standard [for safe charging of lithium-ion batteries], provide guidelines so if the temperature overshoots a certain level, the charging rate slows down to cool down the devices. But now that fast charging becomes very slow charging and it takes longer to charge,” she said. “With our solution not only do you get 4× faster charging it’s very cool with a maximum 5° temperature rise.”

SIMO charger delivers 4× faster charging with only a 5°C rise in temperature. Click for a larger image. (Source: Analog Devices, Inc.)

“Personalized health care will keep growing and that market is exploding with more and more of these battery-powered gadgets,” said Gopalan. “We continue to see this trend of more and more sensors, thermal management, GPS tracking, and AI processing; all getting packed into these tiny gadgets.”

The MAX77659 is available now in a 30-bump 2.55 × 2.37 × 0.5- mm WLP package. An evaluation kit, the MAX77659EVKIT, also is available.