1. Introduction
In power electronic applications, boost converters are commonly used to step up the input voltage to meet specific load requirements. They are widely utilized in renewable energy systems (such as solar inverters), electric vehicle chargers, and portable electronic devices. These applications require efficient voltage conversion and stable output to ensure the proper operation and longevity of the equipment. Portable electronic devices, such as smartphones and tablet computers, rely on batteries as their primary power sources. To prolong service time, a high-performance power management integrated circuit (PMIC) is an essential component [
1,
2,
3]. With the rapidly increasing computational demands of these devices, the regulator must exhibit several key characteristics [
3,
4,
5,
6], including the following: (1) a high conversion efficiency across a wide load range, (2) a fast transient response to large load changes, and (3) a compact chip area along with a simplified architecture to meet the requirements of handheld devices.
Ripple-based control regulators, characterized by high efficiency, fast transient response, and simple structure, are well-suited for compact and energy-efficient applications [
6]. Among various control schemes, the hysteretic control scheme is particularly favored in high-performance converter designs due to its ease of implementation and inherent pulse-frequency modulation function in discontinuous conduction mode (DCM) [
6,
7,
8].
Figure 1 illustrates the simplest structure of a voltage-mode hysteretic control for a buck converter. The control circuit utilizes only a hysteretic comparator, without requiring an error amplifier or an external clock signal generator. However, to enhance the noise margin and stabilize the system, a large capacitor with significant equivalent series resistance (ESR) is necessary, which unfortunately degrades overall efficiency.
A current-mode (CM) hysteretic control, as shown in
Figure 2a, senses the inductor current ripple and combines it with V
FB to form the feedback voltage V
SEN [
8,
9,
10]. The ESR has a minimal impact on the system’s stability, and overall efficiency is further improved by using a small ESR.
Figure 2b depicts a typical implementation of the current sensor using an RC network across the inductor. The voltage across the capacitor captures the inductor current ripple and adds it to Vo. By appropriately adjusting the ratio between the parallel RC network and the inductor, a significant ripple voltage can be effectively generated. While the feedback voltage V
SEN indirectly regulates Vo, a larger inductor series resistance (DCR) can introduce static error in the output voltage and degrade the load regulation performance. The work in [
10] proposes a quasi-V
2 hysteretic control to overcome this drawback, but it introduces an error amplifier, compromising circuit simplicity. Another approach, presented in [
11], introduces a method of digital hysteretic average current control in a non-inverting buck-boost converter to improve the reference transient performance and achieve smooth mode transitions. Additionally, [
12] presents a time-based dual-mode control asynchronous boost converter, enabling a lower peak current and high integration for improved efficiency.
Meanwhile, different converter topologies present distinct implementation difficulties for CM hysteretic control. As shown in
Figure 3, CM hysteretic control can be easily applied in the buck converter since the inductor current i
L and the output voltage ripples are in phase [
13]. However, in a typical boost converter, the output capacitor current i
C is related to the inductor current in discontinuity. As a result, the output voltage ripples can only be indirectly utilized and require a complex circuit to combine the output voltage and the anti-phase inductor current.
Figure 4 illustrates several CM techniques for dc-dc converters [
14]. An RC-based dc resistance (DCR) current sensor can accurately replicate the waveform of the inductor current with the fastest sensing response when the time constant of an RC network aligns with that of the inductor (L) [
15]. However, in boost converters, the sensing gain is small, and the sensing output is often out of phase with the inductor waveform due to the reversed position of the inductor compared to buck converters. Despite this limitation, a SenseFET-based current sensor allows for in-phase current sensing across various converter topologies. Alternatively, integrating a feedforward-path current sensor with an operational transconductance amplifier (OTA) can improve sensing response time by eliminating the feedback loop, thus avoiding stability issues [
16,
17,
18]. However, the nonlinearity of the transconductance (GM) may compromise sensing accuracy when dealing with a wide range of sensing currents.
Figure 5 illustrates two variations in previously documented hysteretic controlled boost converters. In
Figure 5a [
19], a current-mode hysteretic inner loop is established by monitoring the inductor current, and the output is regulated by an error amplifier that governs the inner loop. This setup achieves decent regulation due to the high-gain amplifier; however, its compensation capacitor may significantly impair transient responses, and the current sensor adds to the design’s complexity and the power budget. In
Figure 5b [
20], a design is presented that combines the output voltage and inductor current information using three transconductance (gm) stages. In this configuration, as the anti-phase inductor current is superimposed onto the output voltage, regulation is attainable, and fast responses are achieved through zeroth-order control, which enhances transient response at the expense of additional inductor energy and circuit complexity.
From the literature review above, an area-efficient current-mode (CM) hysteretic control boost converter with superior regulation performance, fast transient response, and compact structure is preferred. In this paper, we propose a simple anti-phase AC-coupling current emulator, which effectively combines the output voltage and anti-phase inductor current in the boost converter. Additionally, we introduce a high-speed hysteresis window tunable comparator, which is adaptively adjusted using a phase-locked loop (PLL) to achieve a pseudo-fixed switching frequency over a wide range of operating conditions. This design aims to provide fast response and stable and precise regulation.
The rest of this article is organized as follows.
Section 2 provides an explanation of the operational principle and circuit implementation of the proposed scheme. In
Section 3, the measurement results are presented, followed by the discussion in
Section 4.
Table A1 and
Table A2 in
Appendix A list the meanings of the main abbreviations and variables appearing in the text.
3. Measure Results
Using a 180 nm CMOS process, we successfully implemented and validated the proposed hysteretic boost converter. The layout and die photograph of the prototype, occupying an approximate chip area of 1.24 mm
2, are presented in
Figure 15.
The prototype is designed to operate within an input voltage range of 2.7 V to 4.5 V, providing a stable output at 5 V with a load current capacity of up to 400 mA. Load-transient responses were evaluated by varying the load from 0 mA to 300 mA at a 3.3 V input, as illustrated in
Figure 16. Observing the figure, the output voltage (V
O) exhibits undershoot and overshoot values of −42 mV and 38 mV, respectively, with corresponding settling times of 124 μs and 104 μs at 0.1%. Further examination of the magnified sections below reveals that despite load current fluctuations of approximately 500 mA, the output voltage regulation errors remain insignificant. The impact of inductor DC resistance (DCR) on load-dependent regulation errors is effectively mitigated, and the waveforms of the load current indicate minimal peaking, demonstrating robust stability margins and well-optimized loop parameters.
Figure 17 presents the line-transient responses measured under a load current of 300 mA. The observed V
O under/overshoot voltages of −14 mV and 10 mV occur as the supply fluctuates between 3 V and 3.6 V. Additionally,
Figure 18a illustrates the measured load and line regulation performances. Specifically, the converter demonstrates a load regulation of 5 mV/A at an input of 3.3 V and a line regulation of 2.3 mV/V with a load current of 300 mA. Furthermore,
Figure 18b provides a comprehensive overview of the converter’s efficiency and switching frequency across the entire load range. Notably, the converter achieves a peak efficiency of 95.3% while tightly maintaining the switching frequency within ±0.2% of 600 kHz throughout the load range.
4. Discussion
This paper introduces an energy-efficient hysteretic boost converter that incorporates the proposed anti-phase AC-coupling emulate current control and a hysteretic comparator control. The converter utilizes a two-transistor current emulator and a hysteretic comparator to achieve rapid transient responses and precise closed-loop regulations. By adopting this simple scheme, the need for additional control circuits is eliminated, resulting in reduced power consumption and simplified frequency compensation. Additionally, the proposed high-speed high-gain hysteretic tunable comparator allows for a consistent switching frequency of 600 kHz across the entire load range. Experimental results obtained from the prototype, which operates at a quiescent current of 50 μA, demonstrate undershoot and overshoot voltages of −42 mV and 38 mV, respectively, during load transitions ranging from 0 mA to 300 mA. Furthermore, the measured load regulation performance is 5 mV/A, while the line regulation performance stands at 2.3 mV/V.
The performance summary presented in
Table 1 compares the outcomes of the proposed work with those of the prior state-of-the-art boost converters. We can see that our chip has a much smaller area compared to the other models while achieving the highest peak efficiency, the lowest load regulation, and relatively lower line regulation. However, the switching frequency is only 600 kHz, much lower than the other models, and its load current range is also smaller. Therefore, further optimization and improvement are needed in applications requiring high frequency and a large load current.
The current control scheme based on anti-phase AC coupling and the single-lag comparator control method proposed in this study not only achieves innovation in the control algorithm but also demonstrates superior performance through experimental validation in practical applications. This scheme successfully reduces power loss and chip area, simplifies circuit design, and provides high-precision, fast-response voltage regulation. These characteristics make the BOOST converter highly suitable for various applications that require an efficient and stable power supply. For instance, in the battery management system of electric vehicles, the proposed BOOST converter control scheme can effectively enhance energy conversion efficiency, reduce power losses, and thus extend the battery’s lifespan. Furthermore, renewable energy systems, such as photovoltaic power generation systems, can leverage this control scheme to optimize the power conversion process, improving the overall energy utilization of the system. Additionally, the scheme is applicable to various portable devices, where it can provide stable and reliable power support in cases requiring precise and rapid voltage regulation.
By integrating this control method into practical applications, the system’s performance can be significantly enhanced while overall costs are reduced. Based on this scheme, there is potential for its application in a broader range of scenarios in the future, such as applications with higher input voltage ranges, higher switching frequency, or adaptive improvements under varying load conditions. Given its low power consumption and high performance, this approach can offer a new technological pathway for efficient power supply design, with practical benefits across various fields.
