An Emulated Peak/Valley Curve Assisted Fast-Transient Buck Converter Achieving Precise One-Cycle Charge Balance with One-Parameter Calibration

In high-performance computing applications, a fast-transient and high-efficiency buck converter is crucial. It is desirable to achieve one-cycle charge balance (OCB) that minimizes the undershoot/overshoot (US/OS) voltage and the recovery time $(\mathrm{t}_{\text{US}}/\mathrm{t}_{\text{OS}})$, under a rapid load current change $(\Delta \mathrm{l}_{\text{LOAD}})$. Fig. 1 explains how to achieve OCB for a buck converter. It detects an $\mathrm{l}_{\text{LOAD}}$ step-up at $\mathrm{t}_{0}$ and turns on the high-side switch instantly, raising the inductor $(\mathrm{L}_{\mathrm{O}})$ current $\mathrm{l}_{\mathrm{L}}$ that intersects $\mathrm{l}_{\text{LOAD}}$ at $\mathrm{t}_{1}$ (the output capacitor $\mathrm{C}_{\mathrm{O}}$ 's current $\mathrm{l}_{\text{CO}}=0$). After that, $\mathrm{V}_{\text{OUT}}$ begins to recover to the reference voltage $\mathrm{V}_{\text{REF}}$, The high-side switch turns off at $\mathrm{t}_{2}$ and hence $\mathrm{l} _{\mathrm{L}}$ ramps down, crossing $\mathrm{l}_{\text{LOAD}}$ at $\mathrm{t}_{3}$. Clearly, if we detect $\mathrm{t}_{0}$ and $\mathrm{t}_{1}$ accurately, t2 can be derived from eq. (1)–(2), ensuring the areas $\mathrm{Q}_{1}=\mathrm{Q}_{2}$ and thus OCB. Similarly, we can achieve OCB under an ILOAD step-down if $\mathrm{t}_{2}$ is obtained from eq. (3)–(4). This scheme is also applicable to a low-slew-rate $\Delta \mathrm{l}_{\text{LOAD}}$, where the resultant $\mathrm{Q}_{2}$ is slightly larger than $\mathrm{Q}_{1}$ (almost OCB). Hysteretic control [1]–[3] can realize fast $\mathrm{t}_{0}$ detection, but it fails to detect $\mathrm{t}_{1}$ for OCB. [4]–[5] used capacitor current sensor (CCS) for precise $\mathrm{t}_{1}$ detection. However, the mismatches on Co, equivalent series resistance ESR, and inductance ESL undermine the detecting accuracy. Fig. 1 compares the detected signal $\mathrm{V}_{\text{SENS}}$ with $\mathrm{l}_{\text{CO}}$ under ESR mismatch, where the zero-crossing point $(\mathrm{t}_{1})$ detection lags behind. Therefore, the CCS schemes should calibrate three parameters $\mathrm{C}_{\mathrm{O}}$, ESR, and ESL, assisted by high-accuracy inductor current sensors and hence complexing the design.