Designing Hearables? Tiny PMICs Boost Battery Life

August 8, 2017

By: Christine Young
Blogger, Maxim Integrated


Hearables have been called the next big consumer thing, enhancing hearing and understanding via applications such as sound control, noise cancellation, speech amplification, and even real-time language translation. Looking ahead, these in-ear micro-computers will encompass much more than hearing aids and other listening devices. Development is already underway on hearables with capabilities such as heart rate monitoring and measurement of other biometrics, activity tracking, and even personal identification.

Probably the biggest challenge around designing hearable applications stems from their tiny form factors. Think about earbuds – smaller than your thumb, they’re still expected to deliver rich sound with long battery life. Other design requirements:

  • Efficient power management
  • Increased memory
  • Faster processing
  • Higher accuracy
  • High level of integration
  • Low bill-of-materials (BOM) cost 

Needless to say, power and battery management for hearable designs is tough. Since hearables can support only tiny batteries, they need very accurate fuel gauges to assess and maximize battery life to prevent sudden or early shutdowns. For battery management, Maxim offers its highly accurate ModelGauge battery fuel gauge ICs, which save cost and space since they do not require current-sense resistors and other external components. 

On the power management side, circuits should be compact, highly efficient, and have low quiescent current. Ideally, they should support multiple battery types and provide the variety of rails needed for different circuit blocks. Keeping in mind the miniature form factor, ideal power management ICs (PMICs) for hearables should integrate multiple functions, such as regulation and charging. A wide input voltage range is essential if you want to support various battery types over their full range (full charge to near empty). Also important is the fact that PMICs have independent regulators, which improve solution efficiency by allowing individual power rails to be tailored to specific system needs. 

EarbudsGiven their tiny size, earbuds need PMICs that are low power, highly efficient, and small.

New PMICs for Space-Constrained Designs

Maxim has launched two new ultra-low-power PMICs that address the challenges of hearables, wearables, and other space-constrained internet of things (IoT) applications, particularly those powered by lithium-ion batteries. The MAX77650 and MAX77651 PMICs integrate regulators, chargers, and current regulators for LED indicators into a 19.2mm2 space—less than half the size of existing component combinations. By contrast, most PMICs for products using lithium-ion batteries rely on additional discrete components. What makes these PMICs truly unique, according to Scott Kim, executive business manager in Maxim’s Mobile Solutions Business Unit, is their single inductor multiple output (SIMO) buck-boost regulators. The SIMO regulators provide three independently programmable power rails from a single inductor, 150mA low dropout (LDO) regulators, and three current sink drivers, reducing overall component count while maximizing available board space. The ICs provide some key advantages:

  • Lowest standby power: 0.3µA, with 5.6µA operating current
  • High efficiency: 3-output SIMO channels and LDO extend lithium-ion battery life
  • Smallest solution size: reduced component count due to multi-channel SIMO regulator 

The regulators in this configuration deliver highly accurate power regulation, extending lithium-ion battery life with high efficiency while reducing power-wasting heat dissipation. For flexibility and ease of use, each output automatically assumes buck, boost, or buck-boost operating mode. Also, these aspects are all programmable:

  • VOUT, from 0.8V to 5.25V
  • Peak inductor current
  • Programmable power-up/down sequencing 

The MAX77650 and MAX77651 also feature a low-power linear charger that provides safe charging with designs that have small batteries. Charger features include:

  • 7.5mA to 300mA programmable fast-charge current
  • Accurate termination currents down to 0.75mA
  • Battery regulation voltage that’s programmable from 3.6V to 4.6V

Evaluation kits are available for both PMICs, so you can test drive them for your next hearable design.