[Introduction]ROHM (headquartered in Kyoto, Japan), a world-renowned semiconductor manufacturer, has established a new power supply technology “QuiCurTM” that improves the load response characteristics of various power supply ICs including DC/DC converter ICs*1 ( Hereinafter, referred to as “response performance”, it refers to the response speed and voltage stability of the post-stage circuit during operation).
In recent years, in various application fields, the process of digitization has been accelerated, and with the increase in the number of Electronic components installed, the design man-hours of applied products have also increased. Among them, capacitors are widely used in many applications, such as applications for stabilizing circuits, and there is an increasing demand for reducing the number of capacitors used. In addition, in power supply circuits, in order to reduce design man-hours when changing specifications, there is an increasing demand for high-quality power supply ICs that are excellent in response performance and that can achieve expected stable operation. These requirements can also be said to be the basic requirements for power supply ICs. In order to meet these requirements, ROHM has established a high-speed load response technology “QuiCurTM” that can maximize the response performance of power supply ICs.
To achieve a stable power supply function, a power supply IC incorporates a circuit (hereafter referred to as a “feedback circuit”) that fine-tunes the output voltage by constantly monitoring the output voltage and comparing it with a reference voltage inside the IC. If such a feedback circuit can respond faster, it is possible to recover output voltage fluctuations caused by fluctuations in input voltage and load current*1 in a short time. On the other hand, if the response is too fast, the circuit will be unstable, the output voltage will oscillate, and the response speed will also be affected by the capacitance of the output capacitor (hereinafter referred to as “output capacitance”), making it difficult to achieve the target response performance .
By adopting the newly developed high-speed load response technology “QuiCurTM” in the power supply IC, it is possible to prevent instability of the power supply IC feedback circuit and achieve the target response performance to a greater extent. For the output capacitor required by the power supply IC, not only can the capacitance be reduced to a lower level, the number of components and the mounting area of the circuit board can be reduced, but also the capacitance and output voltage fluctuation can be adjusted linearly (the constant is inversely proportional) , the expected stable operation can be easily achieved even when the capacitance is increased due to the specification change, so it is very helpful to significantly reduce the design man-hours of the power supply circuit from the viewpoints of a smaller number of components and a more stable operation .
At present, ROHM is promoting the introduction of power supply ICs using this “QuiCurTM” technology to the market as soon as possible, and plans to provide samples of DC/DC converter ICs in April 2022 and linear regulators in July 2022.
＜About high-speed load response technology “QuiCurTM”＞
QuiCurTM is a trademark named after ROHM’s own circuit “Quick Current” that realizes high-speed load response. Using this technology, the feedback circuit of the power supply IC can achieve the target load response characteristic (response performance) to a greater extent under the premise of stable operation. This technology has the following characteristics, which help to reduce the design man-hours of the power supply circuit of the application product.
1. Can reduce the number of output capacitors and board mounting area
Using QuiCurTM technology can quickly respond to fluctuations in the output voltage relative to the load current, therefore, the output capacitor capacity required for the power supply IC can be reduced, thereby reducing the number of components and board mounting area. Compared with the conventional ROHM technology, the same response performance can be achieved with less than half of the capacitor capacity.
2. The expected stable operation can be easily achieved even when the specifications are changed
As the output capacitor capacity increases, the output voltage stabilizes, but the transient response performance (the time it takes to start responding) deteriorates. Using QuiCurTM technology, even if the output capacitor capacity is increased, the transient response performance will not change, so the output capacitor capacity and output voltage fluctuation can be adjusted linearly (the constant is inversely proportional). Even when a more stable operation is required due to a specification change (when a further reduction in output voltage fluctuation is desired), the expected stable operation can be easily achieved.
＜Details of QuiCurTM technology＞
In order to pursue the response performance to a greater extent, QuiCurTM technology finely divides the signal processing tasks of response speed (control system) and voltage stability (calibration system), and solves the two problems existing in the feedback circuit of power ICs in the past: The low frequency band in front of the stable area creates an unusable area”, “The zero-crossing frequency*2 (f0) varies with the capacity of the output capacitor”.
For the first problem, “generating an unusable area”, this technique successfully solves it by configuring a dedicated error amplifier*3 that does not generate an unusable area in the feedback circuit. For the second problem “zero-crossing frequency variation”, this technology configures a second-stage dedicated error amplifier and adopts a technology that can adjust its gain (Gain) by current drive. Although the zero-crossing frequency varies with the capacity of the output capacitor connected, by adjusting the amplification factor according to this change, the zero-crossing frequency can always be set on the boundary line between the unstable region and the stable control region. A system constructed by separating the roles of these two error amplifiers can be widely used in power supply ICs such as DC/DC converter ICs with feedback circuits and linear regulators.
＜Integration with ultra-stable control technology “Nano CapTM”＞
Nano Cap™ provides stable control of the output of linear regulators by improving the response performance of analog circuits and minimizing wiring and amplifier parasitics, enabling output capacitors to be reduced to 1/1 the capacity of previous technologies 10 or less, therefore, for example, a capacitor on the output side of a linear regulator is no longer required, and only a 100nF capacitor on the microcontroller side can be used for stable operation. With QuiCurTM technology alone, the output capacitor capacity can only be reduced to the order of µF, but when QuiCurTM and Nano CapTM technology are combined, it can be reduced to the order of nF.
For more details about Nano CapTM, please visit: https://www.rohm.com.cn/support/nano
＜Explanation of terminology＞
*1) Load response characteristics (load transient response characteristics) and load current
From the point of view of the power supply IC, the subsequent circuits such as microcontrollers and sensors can be regarded as “loads”. When these loads operate, the current (load current) fluctuates, causing the output voltage of the power IC to drop. The load response characteristic refers to the response time and the stability of the power supply required to recover the voltage dropped due to the fluctuation of the load current.
*2) Zero-crossing frequency (gain zero-crossing frequency, gain crossover frequency)
In semiconductors and application circuits that process feedback circuits such as operational amplifiers and power supply ICs, the frequency at which the circuit’s gain (Gain) becomes 0dB. It is an index indicating load response characteristics and circuit stability (phase margin) without oscillation.
*3) Error Amplifier
It is responsible for extracting the difference between the reference voltage inside the power supply IC and the voltage of the feedback circuit, and controls the power supply output stage according to the extracted difference, and restores the output voltage of the power supply IC to the target voltage.