When you wear your earbuds for a long hike or an afternoon at the gym, you don’t want to be interrupted by having to stop and recharge the earpieces. You expect your hearables, wearables, and other tiny, battery powered electronic devices to perform reliably over long periods of time. From a design standpoint, these user expectations are a tall order to meet. The form factor constraints dictate the need for a small Lithium-Ion battery, which must last a long time between charge cycles and be utilized sparingly. Power supplies, in turn, must meet the distinct and diverse voltage requirements of the sub-systems within the design.
Delivering long battery life in tiny devices
Introducing ‘SIMO’ Single Inductor Multiple Output power architecture solutions from Analog Devices
When you wear your earbuds for a long hike or an afternoon at the gym, you don’t want to be interrupted by having to stop and recharge the earpieces. You expect your hearables, wearables, and other tiny, battery powered electronic devices to perform reliably over long periods of time.
From a design standpoint, these user expectations are a tall order to meet. The form factor constraints dictate the need for a small Lithium-Ion battery, which must last a long time between charge cycles and be utilized sparingly. Power supplies, in turn, must meet the distinct and diverse voltage requirements of the sub-systems within the design.
The SIMO architecture provides an optimal solution for these systems, integrating functionality that would otherwise require multiple discrete components.
In this month’s issue Kevin Doyle, Field Applications Engineer at Anglia gives an insight into what a SIMO architecture is and how it works for buck-boost regulators.
SIMO Regulators
Single Inductor Multiple Output (SIMO) ICs harness the high efficiency of switching converters with the compact, space saving architecture of a single inductor design for multipower rails applications. Analog Devices’ family of single inductor multiple outputs (SIMO) power management ICs provides multiple switching buck-boost regulators using only one single inductor. The high efficiency conversions benefit and extend battery life, while the ultracompact size and low bill of materials provide a perfect solution for space constrained wearables, hearables, IoT and other small form factor battery powered industrial, eHealth and consumer devices.
Additional integrated functionalities and features further simplify the design of low power portable devices by incorporating functions such as battery management (charger and fuel gauging), LDO outputs for noise-sensitive rails and on-board sequencing for controlled power-up and power-down. Additionally, an I2C interface provides the capability to enable complete customization of the power management IC and supports dynamic voltage scaling (DVS) for additional power savings and custom power profiles.
SIMO Architecture
In a traditional multiple switching regulator topology, each switching regulator needs a separate inductor (Figure 1). The inductors can be physically large and costly, this is a major disadvantage for small form factor products. The other option is to use linear regulators, which are fast, compact, and low noise, but have higher power dissipation. There’s also the hybrid alternative of using multiple low-dropout regulators (LDOs), in conjunction with DC-DC converters. However, while this configuration would result in intermediate power and heat dissipation, it still yields a larger design than LDOs alone.
Figure 1: Traditional Architecture for Buck-Boost Switching Regulator and the MAX77643 SIMO
The featured buck-boost SIMO converter can regulate up to three (four on the MAX77655) output voltages over wide output voltage ranges using a single inductor. The buck-boost topology helps to better utilize the inductor since it requires less time to service each channel compared to a buck-only SIMO.
A buck-only SIMO will suffer when an output voltage approaches the input battery voltage. Presently, a buck-only SIMO requires the inductor for too much time, which impacts the other output channels. The topology of the SIMO buck-boost is outlined in Figure 2.
Figure 2: SIMO Architecture
Note: the flow arrows are illustrative only and do not represent current flow at any specific time.
As shown in Figure 2, under the control of the “Service On 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
Designing products for the wearable, portable and IoT market with low power requirements and multiple voltage rails, 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.
Figure 3: Saving PCB Real Estate & reduction of BOM Content
In this design example, the MAX77658 SIMO device integrates the power management integrated circuit (PMIC) providing flexibility to enable/disable power blocks when required to make the most of the tiny batter capacity normally available, enabling the device to operate for a longer period between charges. This PMIC integrates the power tree, administering power sequencing and switching, protection, monitoring, and control to bring the maximum system efficiency
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 available on www.anglia-live.com. This design tool has an excellent spreadsheet facility to allow the designer to explore the trade-offs of associated with the different SIMO parameters.
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.
Visit www.anglia-live.com to see the full range of Analog Devices products available from Anglia.
References
My thanks to extracts from Analog Devices publications and discussions attributed to:
· Cary Delano, Distinguished Member of Technical Staff and Gaurav Mital, Product Line Director: “SIMO Switching Regulators: Extending Battery Life for Hearables and Wearables”.
· Norberto Sánchez-Dichi and Mohamed Ismail: Application Note 6628: “How a SIMO PMIC Enhances Power Efficiency for Wearable IoT Designs”.
· Kevin Nguyen, Snr Product Line Manager, Battery & Consumer Power.
