The internet of things (IoT) manages a large infrastructure of web-enabled smart devices, small devices that use embedded systems, such as processors, sensors, and communication hardware to collect, send, and elaborate on data acquired from their environment. Thus, from a practical point of view, such devices are composed of power-efficient storage, scalable, and lightweight nodes needing power and batteries to operate. From the above reason, it appears clear that energy harvesting plays an important role in increasing the efficiency and lifetime of IoT devices. Moreover, from acquiring energy by the surrounding operational environment, energy harvesting is important to make the IoT device network more sustainable from the environmental point of view. Different state-of-the-art energy harvesters based on mechanical, aeroelastic, wind, solar, radiofrequency, and pyroelectric mechanisms are discussed in this review article. To reduce the power consumption of the batteries, a vital role is played by power management integrated circuits (PMICs), which help to enhance the system’s life span. Moreover, PMICs from different manufacturers that provide power management to IoT devices have been discussed in this paper. Furthermore, the energy harvesting networks can expose themselves to prominent security issues putting the secrecy of the system to risk. These possible attacks are also discussed in this review article.

Energy Harvesting towards Self-Powered IoT Devices

A regulator includes a transistor connected between an input and an output. A feedback voltage controls the transistor to keep the output voltage constant. A first circuit functions as a comparator to compare a detection voltage from the output of the transistor and the feedback voltage when the output current is higher than a predetermined value, and functions as a buffer when the output current is lower than the predetermined value. A second circuit receives a reference voltage, the feedback voltage, and an output from the first circuit, and generates (i) a difference between the feedback voltage and the first circuit output when the reference voltage is lower than the first circuit output, and (ii) a difference voltage between the feedback voltage and the reference voltage when the reference voltage is higher than the first circuit output, and supplies a control voltage to control the output of the transistor.

Semiconductor integrated circuit for regulator

Disclosed is an electronic control unit capable of identifying an abnormality in a power supply voltage without narrowing the operating voltage range, and having minimal effects on cost and the circuit mounting surface area. The ECU includes a microcomputer containing an input terminal VCCin and an input terminal Vrin, a power supply IC that supplies a power supply voltage VCC to the input terminal VCCin, and as a reference-voltage-generator circuit a voltage-divider resistor and a voltage-divider resistor configuring a voltage-dividing circuit that outputs a sub-divided voltage Vc is sub-divided from the power supply voltage VCC, a capacitor coupled at one end to the input terminal Vrin and coupled on at the other end to ground, and a voltage isolation element coupled between the voltage-dividing circuit and the input terminal Vrin.

Electronic control unit

In this paper, we propose a fully integrated switched-capacitor DC–DC converter with low ripple and fast transient response for portable low-power electronic devices. The proposed converter reduces the output ripple by filtering the control ripple via combining a low-dropout regulator with a main switched-capacitor DC–DC converter with a four-bit digital capacitance modulation control. In addition, the four-phase interleaved technique applied to the main converter reduces the switching ripple. The proposed converter provides an output voltage ranging from 1.2 to 1.5 V from a 3.3 V supply. Its peak efficiency reaches 73% with ripple voltages below 55 mV over the entire output power range. The transient response time for a load current variation from 100 μA to 50 mA is measured to be 800 ns. Importantly, the converter chip, which is fabricated using 0.13 μm complementary metal–oxide–semiconductor (CMOS) technology, has a size of 2.04 mm2. We believe that our approach can contribute to advancements in power sources for applications such as wearable electronics and the Internet of Things.

Fully Integrated Low-Ripple Switched-Capacitor DC–DC Converter with Parallel Low-Dropout Regulator

This paper presents an ultra-low-power solar energy harvesting system with a power management module (SEHS-PMU) for the Internet-of-Things (IoT) applications. The voltages generated are suitable for the IoT sensors used for smart cities as well as Internet-of-Medical-Things (IoMT) based biomedical applications. The SEHS-PMU is harvesting energy from the solar cell, and it can provide regulated voltages of 3.3 V, 1.8 V, 1 V, and 0.5 V. The harvesting mechanism leads to battery-less IoT, and is safe for the humanity and environment. Charge pumps (CP) are used as a boost and buck converter, which is suitable for monolithic integration. Low drop-out regulators (LDOs) are used for regulating the loads. A digital controller controls the selection of loads as per requirement for saving the power. The SEHS-PMU is designed in CMOS 180 nm technology library.

A Solar Based Power Module for Battery-Less IoT Sensors Towards Sustainable Smart Cities

A switching converter (DC-DC) cascaded with a low dropout regulator (LDO) gives the best trade off in terms of high system efficiency and low output ripple for automotive power management applications. The dropout voltage of the LDO is fixed based on its peak load. An adaptive LDO dropout technique, based on LDO load-current sensing, has been proposed to improve the moderate and light load system efficiency of the cascaded DC-DC and LDO combination. The feedback from LDO output to DC-DC output is stable and has minimal overhead (< 2%) in terms of area and current consumption. The 1V LDO with adaptive dropout gives an efficiency improvement of 74% for 1A load to 81.6% for 100uA load across input voltage range of 6V to 18V. The overall hybrid regulator efficiency improvement upto 5% is achieved in simulations using 0.35μm AMS H35 process.

Automotive hybrid voltage regulator design with adaptive LDO dropout using load-sense technique

This paper proposes a novel method for ripple cancellation in multi-phase converters. Unlike the conventional multi-phase converter, the proposed topology can cancel the ripple irrespective of the duty ratios. The proposed topology is designed to give 3.3V output for wide supply range of 4.5 to 18V and load range of 0 to 3A in AMS 0.35um high-voltage CMOS process. Transistor level simulation results validate that the proposed method can reduce the ripple by 80% in a multi-phase converter. Cancelling the current ripple at the output allows the inductors and capacitors to be sized much smaller compared to the state of the art reported designs.

A low-cost multi-phase 3A buck converter with improved ripple cancellation for wide supply range

A switching converter (DC-DC) cascaded with parallel low dropout regulators (LDO) gives the best trade off in terms of high system efficiency and low output ripple for automotive Power Management ICs (PMIC). The minimum DCDC output voltage is dependent on the highest LDO output and its corresponding dropout voltage. An adaptive LDO dropout technique based on Maximum Load Current Selector (MLCS) circuit has been proposed to improve the moderate and light load system efficiency of the cascaded DC-DC and multiple LDO combination. The input currents to the MLCS circuit is provided by current scaler circuit. The proposed circuit has been designed in AMS 0.35 m High-Voltage CMOS process and simulated across wide supply voltage (6V to 18V), wide load range (2mA to 300mA) and wide temperature range (-40°C to 150°C) to meet the automotive requirements. The adaptive dropout scheme works for any output voltage and load current of the LDOs. The overall system efficiency is improved by about 3% to 10% with minimal overhead (< 2%) in terms of area compared to conventional fixed dropout architecture.

System Efficiency Improvement Technique for Automotive Power Management IC Using Maximum Load Current Selector Circuit

A switching converter (dc–dc) cascaded with parallel low-dropout (LDO) regulators gives the best tradeoff in terms of high system efficiency and low output ripple for automotive power management ICs (PMICs). The minimum dc–dc output voltage is dependent on the highest LDO output and its corresponding dropout voltage. An adaptive LDO dropout technique based on maximum load current selector circuit has been proposed to improve the moderate and light load system efficiency of the hybrid PMIC with dc–dc supplying three independent LDO regulators. The circuit has been fabricated in AMS 0.35- $\mu \text{m}$ high-voltage CMOS process and tested across wide supply voltage of 6–18 V, wide temperature range of −40 °C to 150 °C, and maximum load of 450 mA to meet the harsh automotive application requirements. The adaptive dropout circuit has minimal overhead (<2%) in terms of area compared to fixed dropout architectures and negligible current consumption overhead. The overall system efficiency improvement of about 3%–10% is achieved with adaptive dropout scheme as per the experimental results. The concept is independent of dc–dc and LDO architecture and can be extended to many system-on-a-chip-based power supplies with dc–dc and LDO combination.

A 6–18 V Hybrid Power Management IC With Adaptive Dropout for Improved System Efficiency Up To 150 °C

This paper describes the system design considerations and challenges faced during the design of automotive power management ICs (PMIC). Rear view camera have been considered as a case study because of wide spread acceptance as driver assistance systems. Optimal IC architectures with DC-DC and LDO combination and their trade-offs have been carefully analyzed. Key considerations regarding automotive transients, high temperature, IC technology, package and pinout have been analyzed and a two-chip architecture has been proposed as an optimal partitioning between cost, efficiency and reliability in harsh automotive environment.

Krishna Kanth Gowri Avalur

Papers

Automotive hybrid voltage regulator design with adaptive LDO dropout using load-sense technique

A low-cost multi-phase 3A buck converter with improved ripple cancellation for wide supply range

System Efficiency Improvement Technique for Automotive Power Management IC Using Maximum Load Current Selector Circuit

A 6–18 V Hybrid Power Management IC With Adaptive Dropout for Improved System Efficiency Up To 150 °C

Power management IC architecture in automotive environment: Case study of rear view camera