In wearables, optical-sensing accuracy is impacted by a variety of biological factors unique to the user. Designers have been striving to increase the sensitivity of optical systems, in particular the signal-to-noise ratio (SNR), to cover a broader spectrum of use cases. Traditional low-quiescent-current regulators favored in wearable applications come with tradeoffs that degrade SNR on the wrist, such as high-amplitude ripple, low-frequency ripple and long-settling times. Some designers have even turned to high-quiescent-current alternatives to overcome these drawbacks, but they must deal with increased power consumption, which reduces battery runtime or requires a larger battery.
The MAX20345 features a first-of-its-kind buck-boost regulator with low ripple at high frequency that will not interfere with the highly sensitive heart-rate, blood-oxygen (SpO2) and other optical measurements. The regulator delivers the desired low-quiescent-current performance without the drawbacks that degrade SNR and, as a result, can increase performance by up to 7dB (depending on measurement conditions).
The PMIC integrates a lithium-ion battery charger; six voltage regulators, each with ultra-low quiescent current; three nanoPower bucks (900nA typical) and three LDO regulators with ultra-low quiescent current (as low as 550nA typical). Two load switches allow disconnecting of system peripherals to minimize battery drain. Both the buck-boost and the bucks support dynamic voltage scaling (DVS), providing additional power-saving opportunities when lower voltages can be deployed under favorable conditions.
“With sales of fitness and wellness wearable electronics expected to rise to over 114 million units by 2020, there is increasing demand for better, more precise sensing technology for measuring health vitals including heart rate and blood-oxygen levels,” said Kevin Anderson, senior analyst for power semiconductors at IHS Markit.