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Digital Hybrid Ripple-Based Constant On-Time Control for Voltage Regulator Modules

Fig. 1. Comparison of the control-to-output transfer function of the analog enhanced ripple-based con-trol scheme with capacitor combinations.
This paper presents a digital hybrid ripple-based constant on-time control scheme for voltage regulator modules (VRMs). Due to the sampling effects of the digital implementation, stability issues become worse than in analog ripple-based control schemes, especially when low-ESR decoupling capacitors are used to filter output. In order to stabilize the system and fulfill the output impedance requirements of adaptive voltage positioning (AVP), a hybrid ramp compensation strategy, which includes the external ramp and the estimated current ramp, is proposed. A small-signal model of the proposed architecture is derived to provide the design guideline for the ramp compensation gains and the number of output and decoupling capacitors. In addition, only low sampling-rate Analog-to-Digital Converters (ADCs) are required to sample the input voltage, the output voltage, and the average current, making the proposed architecture compati-ble with the cost/complexity constraints of VRM applications. Simulation and experimental re-sults show that the ripple-based control scheme can be used to achieve high-bandwidth perfor-mance, and the proposed digital control architecture can fulfill the AVP design requirements of single-phase VRMs.


Fig. 2. Comparison of the output impedance transfer function of the analog enhanced ripple-based con-trol scheme with capacitor combinations.
Fig. 3. Theoretical and simulated frequency response of the output impedance of the proposed hybrid ripple-based constant on-time control scheme.
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