QuiCur maximises the response performance of power supply chips
Rohm has developed a new power supply technology that improves the load transient response characteristics for DC-Dc converters and Low Drop Out regulators (LDOs)
The QuiCur technology involves response speed, and voltage stability of subsequent stages to allow a frequency boost to 300kHz with fewer external components.
Power supply ICs are used to monitor the output voltage to ensure stable power supply functionality and includes a feedback circuit that fine-tunes the output voltage by comparing with an internal reference voltage. Providing faster response makes it possible to reverse changes in the output voltage caused by fluctuations in input voltage and/or load current in a shorter time.
However, shortening the response time too much can cause the circuit operation to become unstable and the output voltage to oscillate, and as the response speed is also affected by output capacitance. Until now it has been difficult to achieve the desired response performance.
The QuiCur technology solves the two problems of conventional power supply IC feedback circuits when pursuing maximum response performance. The first addresses the unusable region generated in the frequency range lower than the unstable area. The second addresses variations in the zero-cross frequency (f0) due to the output capacitance by fully dividing the roles of signal processing for response speed (control system) and voltage stability (compensation system).
The first problem was solved by using a dedicated error amp that does not generate an unusable area in the feedback circuit. The second is addressed with a dedicated second-stage error amplifier with a design that allows the gain to be adjusted by current drive.
Although the zero-cross frequency may vary depending on the connected output capacitance, by adjusting the amplification factor, the zero-cross frequency can always be set at the limit (on the boundary line) between the unstable and stable control regions. This system, in which the roles of the two error amps are shared, is widely applicable to power supply ICs such as DC-DC converter ICs and LDOs that incorporate feedback circuits.
Not only can the number of external components and mounting area be reduced by minimizing the capacitance of the output capacitor required by the power supply IC, but linear adjustment of the capacitance and output voltage fluctuations (negative constant proportional relationship) is enabled, ensuring stable operation even when the capacitance increases due to specification changes. This contributes to a significant reduction in power supply circuit design resources by providing stable operation with fewer external components.
Although QuiCur can reduce the output capacitance to the order of µF, combining with Nano Cap brings this down to the order of nF.
Nano Cap provides stable control of the linear regulator output by improving response in analog circuits while minimizing parasitic factors related to wiring and amplifiers. This allows the output capacitance to be reduced to less than 1/10th that of conventional solutions, eliminating the need for a capacitor at the output of the linear regulator and ensuring stable operation with just a 100nF capacitor at the MCU side.
Rohm is currently working to commercialize QuiCur power supply ICs, with plans to ship samples of DC-DC converter ICs in April and LDOs in July 2022.
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