“The wireless IoT industry is producing a large number of battery-powered devices (Figure 1). While the basic battery management system is easy to understand, specific configurations vary by battery technology (primary, secondary, chemistry, or form factor) and load constraints (voltage, current, or noise sensitivity).
The wireless IoT industry is producing a large number of battery-powered devices (Figure 1). While the basic battery management system is easy to understand, specific configurations vary by battery technology (primary, secondary, chemistry, or form factor) and load constraints (voltage, current, or noise sensitivity). With all these variables, it seems that we should take a discrete approach to designing the system: a dedicated IC for each module, such as the typical system shown in Figure 2. However, this approach contradicts other important requirements of such portable, lightweight devices, especially the requirement of small size. This article explores three very important portable applications and demonstrates that even if multiple modules are required, an integrated power management approach tailored around SIMO core converters can easily solve this challenge.
Figure 1. Wirelessly connected IoT devices
Integrated Power Design Methodology
Traditional solutions typically use multiple switching regulators and associated inductors or use multiple linear regulators. For portable power management, the single-Inductor multiple-output (SIMO) architecture addresses the power inefficiencies and size issues faced in traditional solutions.
Compared to other methods, SIMO solutions provide higher power in less space, support longer battery life and smaller form factors.
While SIMO converter ICs represent a major step forward in integration, additional functionality may be required to meet more complex system requirements. This brings up the question: is it possible to integrate the core SIMO converter with various levels of auxiliary functions, thereby implementing the entire power management system in a single IC?
In the following case studies, we address this question by applying SIMO technology to three distinct portable applications.
Typical Rechargeable Battery System
Figure 2 shows a typical rechargeable battery system. When there is an AC adapter, the AC adapter charges the battery through the charger and supplies power to the load through SW2; in the absence of an adapter, the battery takes over and supplies power to the system through SW1. Due to space and cost constraints, it is often necessary to use multiple LDOs while utilizing a single switching regulator (BUCK) to power the heaviest loads. One or more LED drivers may also be required to support IR remote control or RGB signals.
Figure 2. Typical Hearable Device Power Flow Diagram
In the following sections, we customize the system for three different applications.
SIMO PMIC rechargeable battery system
Figure 3 shows a fully integrated SIMO PMIC solution to support a rechargeable battery system. This scheme uses two buck-boost switching regulators (BB3, BB2) to replace the LDO (LDO3, LDO2 in Figure 2) to efficiently power two loads. A third buck-boost regulator (BB1) replaces the BUCK in Figure 2. Integrated LDO1 for noise sensitive loads. The solution also integrates the LED driver. Finally, the charger and switch in Figure 2 are also integrated into the charger and power path module in Figure 3.
The power efficiency and size advantages of using SIMO switching regulators compared to using linear regulators are obvious. By using a buck-boost regulator, it can regulate even when the input voltage drops below the output voltage, using up the last drop of energy from the battery.
Figure 3. Rechargeable battery system using SIMO PMIC1
Case Study: Rechargeable Remote Control
Rechargeable remotes such as TVs or smart homes require a power management system, including a charger and an IR LED driver.
For these systems, SIMO PMICs are ideal. The PMIC in Figure 5 uses a linear charger (375mA), a triple-output SIMO buck-boost regulator (300mA total), an LED driver (425mA), and an LDO (50mA). A bidirectional I2C interface allows configuration and checking of device status.
Figure 4 shows the implementation of the charger and switch in the PMIC. An intelligent power path circuit distributes power between the system (SYS) and the battery. When the AC adapter is used as the power source, the input control loop regulates the system voltage (SYS) to 4.5V (VSYS-REG). In this case, the charger (transistor T2and its associated controls) are powered by the SYS pin and charge the battery. In the event that the AC adapter does not provide input power, the battery passes through the T2Supply power to IC circuits and system loads. Compared to the configuration in Figure 2, since T2This configuration has higher silicon efficiency as both a pass transistor for the linear charger (with an AC adapter) and a switch (without an AC adapter).
Figure 4. Smart Power Path
Thanks to its SIMO switching regulator and high-efficiency biasing LDO, the small form factor PMIC (in a 2.15mm x 3.15mm x 0.5mm WLP package) provides power with minimal losses and only 21mm of PCB space2, less than half of the common implementation method. The scheme layout shown in Figure 5 takes into account all passive and active components.
Figure 5. SIMO PMIC1 solution (21mm2)
In addition, the PMIC consumes only 300nA in standby mode, which is at least 2 times better than other available solutions. This capability and its efficiency gains extend valuable battery life, help reduce system size by using the smallest battery, and extend the time between charges.
SIMO PMIC non-rechargeable battery system
In Figure 6, the smaller PMIC2 implements all the necessary functions for a non-rechargeable battery system.
Figure 6. Non-rechargeable battery system using SIMO PMIC2
Case Study: Non-Charging Activity Monitors
Activity monitors and insulin pens use LEDs for various functions and are usually powered by AA or AAA cylindrical batteries. The smart insulin metering device helps fill the pen with the correct amount of insulin and lights up an LED when the filling is complete. Activity monitors such as physical activity, seizure and sleep monitors are worn on the wrist like a watch. The light from the LEDs is tuned to a variety of different frequencies and penetrates the skin. Photodetectors detect modulated signals reflected from blood and body tissue, providing information about a patient’s physical activity, such as heart rate, movement, and breathing.
SIMO PMICs are ideal for such systems. The PMIC in Figure 7 uses a triple-output SIMO buck-boost regulator (300mA total), 3 LED drivers (3.2mA each), and an LDO (150mA). Bidirectional I2The C interface allows configuration and checking of device status.
The PMIC (in a 2.15mm x 2.75mm x 0.7mm WLP package) is packaged in the smallest PCB area (16mm2) to achieve power supply. The scheme layout shown in Figure 7 takes into account all passive and active components.
Figure 7. SIMO PMIC2 solution (16mm2)
In addition, the PMIC consumes only 300nA in standby mode and 5.6µA in active mode.
SIMO small size non-rechargeable battery system
In Figure 8, the compact PMIC3 integrates three buck/boost regulators, forming the simplest and smallest size non-charging system implementation.
Figure 8. Non-rechargeable battery system using SIMO PMIC3
Case Study: Coin Cell Battery-Powered Sensors
Humidity and other IoT sensors require small, reliable power management systems for minimum size and maximum operating and shelf life.
SIMO PMICs with low quiescent current are ideal for such applications. The PMIC shown in Figure 9 uses a three-output SIMO buck-boost converter (300mA total). Bidirectional I2The C interface allows configuration and checking of device status.
The PMIC (in a 1.77mm x 1.77mm x 0.5mm WLP package) has a minimal PCB area (14mm2) to achieve power supply. The scheme layout shown in Figure 9 takes into account all passive and active components.
Figure 9. SIMO PMIC3 solution (14mm2)
In addition, the PMIC consumes only 330nA in standby mode and 1.5µA in active mode.
We discuss the challenges in implementing small size and high-efficiency power management systems for battery-operated devices. A tailored integration scheme is proposed to take full advantage of the space and power efficiency of the SIMO architecture by selectively integrating the necessary circuits to support a given complexity into a monolithic PMIC.
We apply SIMO technology to three different portable applications. For each case, SIMO PMICs are tailored to the application for the best results, minimum PCB size and long battery life.
The first PMIC (MAX77278) integrates a linear charger, smart power path, triple-output SIMO buck-boost converter, LED driver, and LDO, making it ideal for rechargeable applications.
The second PMIC (MAX77640) integrates a triple-output SIMO buck-boost converter, 3 LED drivers, and an LDO, providing a tailored solution for non-charging applications.
The third PMIC (MAX17271) integrates a triple-output SIMO buck-boost converter tailored for small-footprint, compact applications.
This tailor-made power management implementation maximizes the space and power efficiency advantages of the SIMO architecture, providing the smallest size and highest efficiency power management solution for portable applications.