This article presents a digital V2 constant on-time control buck converter with adaptive voltage positioning (AVP) and automatic closed-loop output impedance (Zoc) calibration for advanced system-on-a-chip processors. To ensure that the output voltage deviation remains within the desired range, the system is equipped with AVP. For an optimal AVP design, the system includes a second-order digital inductor current sensor for deriving a constant Zoc within a wide bandwidth. A detailed system-level analysis was performed to design the proposed control architecture. Considering the inevitable variation and aging of power stage components, the system is equipped with an online real-time Zoc calibration mechanism established to ensure the performance of AVP control. A prototype chip was fabricated using a 90-nm complementary metal-oxide-semiconductor (CMOS) process. The digital controller was fully realized using a standard cell library. Under a 0.9-A load transient, the measured output voltage could be adequately constrained within a specified 1.1-V and 110-mV AVP window.
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