27.6 Background Capacitor-Current-Sensor Calibration of DC-DC Buck Converter with DVS for Accurately Accelerating Load-Transient Response

摘要

Switching buck converters with dynamic voltage scaling (DVS) for high-efficiency high-performance computing applications need to reduce the output-voltage undershoot/overshoot (V_US/V_OS) and settling time t_S under a large and fast-changing load current (I_load). A multiphase topology with a fast load-transient response meets these requirements. The load-transient response can be accurately accelerated to reduce V_US/V_OS and t_S to near their ideal values by measuring the output-capacitor current I_Co to control the inductor's energizing and de-energizing times, since I_Co instantly reflects the load-current transients. An integrated capacitor-current sensor (CCS) [1] can be used to sense I_Co by emulating the output-capacitor impedance Z_Co: comprising capacitance C₀, the equivalent series resistance R_ESR, and inductance L_ESL. However, I_Co will be inaccurately sensed if Z_Co varies with different output voltages V₀, manufacturing variations, PCB parasitics, temperature, and aging. The state-of-the-art CCS calibration technique [1] for such Z_Co variations is suitable for foreground operation and DVS with pre-characterized V₀ levels, since calibration starts immediately after being enabled and runs continuously until it ends. The CCS in [1] is calibrated with a low-power cost-effective comparator and successive approximation logic, with an acceptable calibration time T_CAL for foreground operation. To broaden the range of applications, this work proposes an ADC-based CCS and a background CCS calibration (BCC) controller. The proposed CCS uses a flash ADC with a dynamic reference to shorten T_CAL. The BCC controller automatically finds a quasi-steady state (QS), namely a short period of steady-state behavior when there is no load transient or DVS event, to trigger CCS calibration, and can interrupt CCS calibration when