Figure 3: Saving PCB real estate & reduction of BOM content
Figure 4. Example of SIMO efficiency achieved
Demand” block: the inductor charging cycle flows through Vsys; each of the subsequent inductor discharge cycles is switched individually by the “Output Order” block for VSBB0, VSBB1 and VSBB2.
Each rail can be individually programmed in a time multiplexed manner which in turn allows them to share the saturation current rating of the inductor, thereby reducing the peak current flow and the size of the inductor required.
Board space saving and power efficiency Wearable IoT devices with lightweight and compact form factors generally require tiny batteries to be integrated, the downside is these batteries have a reduced runtime. Therefore, when the voltage rails are not in use, the device should ideally shut down the unused power rails to conserve energy. To efficiently manage voltage rails in wearable IoT designs, a power management integrated circuit (PMIC) can be used to provide this flexibility by enabling/disabling power rails and blocks when required. Designing products for the wearable, portable and IoT market with low power requirements and multiple voltage rails, also requires a solution that fits in a small PCB space area with energy efficiency and long battery life. With the combined functionality of buck-boost, LDO and battery management all contained within the one compact sized device, the Analog Devices’ SIMO portfolio allows the designer to achieve this limited footprint goal using a device with a single inductor, a typical example of this can be seen in Figure 3.
In this design example, the MAX77658 SIMO device integrates the power management integrated circuit (PMIC), buck-boost regulators and fuel gauge into one device providing flexibility to enable/disable power blocks when required making the most of the small battery capacity typically available, thus enabling the device to operate for a longer period between charges. The PMIC integrates the power tree, administering power sequencing and switching, protection, monitoring, and control to bring the maximum system efficiency.
It should be noted, typical power management systems perform DC-DC power conversion in three distinct forms, with differences in physical size, flexibility, and efficiency. ● Linear regulators—can be fully integrated and have voltage scalability, but are not efficient.
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● Capacitor-based switching regulators—can be fully integrated and efficient, but do not have voltage scalability.
● Inductor-based switching regulators—can be highly efficient and have voltage scalability, but tend not to be fully integrated.
In general, capacitor-based switching regulators—also called charge pumps—aren’t favoured because of their limited output voltage scalability. For example, charge pumps are considered a suitable choice for gate drivers; however, for the circuit blocks in wearables, charge pumps aren’t equipped to output the required current needed at specific voltages.
That’s why for these devices, linear and inductor-based switching regulators provide the most flexible power management. With this type of regulator, it is possible to efficiently step down (buck) the voltage of a fully charged battery while stepping up (boost) a low battery voltage as the battery discharges. As such, the battery powers the device across its full voltage range, maximizing operating time based on the current consumed. The Analog Devices SIMO portfolio utilises these combined topologies to provide the most energy and space efficient solution. An example of the level of efficiency that can be achieved by the SIMO family is shown in Figure 4. The efficiency of a specific circuit is a combination of load constraints, passive component values (inductor/ capacitor/resistor) used and end-users power expectations.
Selection of the SIMO
To help customers choose the correct device for their application, Analog Devices provides the SIMO Calculator. This tool is an excellent spreadsheet facility to allow the designer to explore the trade-offs associated with the different SIMO parameters. This spreadsheet tool can be used to estimate corresponding values for the power budget. Download using the QR code:
In addition to the SIMO Calculator, Analog Devices also provide a product selection table outlining the specifications for each device in the series with links to the various product pages. The full selection of SIMO Regulator products can be
viewed/selected from the table by scanning the QR code: Conclusion
For hearables, wearables, and similarly small, battery- operated electronics, long battery life is essential for customer satisfaction. Compared to traditional buck-boost topologies, the SIMO architecture reduces
component count and often extends battery life. This paper examined PMICs integrated with SIMO switching regulators that are ideal for meeting the challenges of ultra-low-power, space-constrained applications.
Design support
Anglia offers support for customer designs with free evaluation kits, demonstration boards and samples of Analog Devices products via the EZYsample service which is available to all registered Anglia Live account customers. Anglia’s engineering team are also on hand to support designers with power management designs and can offer advice and support at component and system level. This expertise is available to support customers with all aspects of their designs, offering hands on design support along with access to Analog Devices’ vast resource of technical application notes and reference designs.
Scan the QR code or visit
www.anglia-live.com
References
My thanks to extracts from Analog Devices publications and discussions attributed to: n Cary Delano, distinguished member of technical staff and Gaurav Mital, product line director: “SIMO Switching Regulators: Extending Battery Life for Hearables and Wearables”. n Norberto Sánchez-Dichi and Mohamed Ismail: Application Note 6628: “How a SIMO PMIC Enhances Power Efficiency for Wearable IoT Designs”. n Kevin Nguyen, snr product line manager, battery & consumer power.
Components in Electronics March 2023 11
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