An One-Cycle Load Transient Response and 0.81 mV/A Load-Regulation Time-Domain Cascaded-VCO-Controlled Buck Converter for Powering Gaming SoC

Time-domain PWM controlled buck converter offers many advantages such as high switching frequency and compact area; however, it cannot fit the needs of gaming SoC in terms of <1 mV/A precise output load regulation and a fast load transient response to prevent under-voltage crash [1]-[5]. Fig 1 shows the issues of conventional time-domain PWM controlled buck converter for powering gaming SoC. The mismatch of the VCO gain K-VCO shown in the transfer curve inside the bottom of Fig 1 complicates the design. The K-VCO mismatch between two oscillators, VCO FB and VCO REF, leads to the mismatch between the control voltages of two VCOs, and results in an output voltage offset Delta V-OS(= F-SW/ K-vcoREF F-SW/ K-vcoFB). In prior art, the FLL [1], chopping [5], and calibration techniques are developed to mitigate the offset under different loading condition. However, the reported 6.25mV/A [1] and 18mV/A [5] load regulations are still insufficient. Furthermore, when the operating condition varies, such as a load transient event, the relocking and resettling procedure worsen the transient trajectory. The control loop bandwidth (BW) and maximum loading current must be compromised for a stable operation. [1]-[5] show that the load step is limited to below 510mA, and the load transient response is longer than 1.8 mu s even though the FSW is in the range of 10MHz. Besides, the low-cost surface-mount-device (SMD) inductor Ls and multilayer-ceramic capacitor (MLCC) Co could be adopted as the F-SW increases. However, the parasitic components of output inductor L-S and output capacitor Co such as C-Ls and L-Co form an additional resonant loop as shown in top of Fig 1. This loop introduces unwanted switching noise coupled from V-LX to V-O path. For a conventional time-domain controller, the switching noise directly modulates VCO and makes the control loop unstable so that the BW and transient response are further limited.