Improved transient response of controllers by synchronizing the modulator with the load step: application to v2ic

Abstract

Abstract-V2 I C is a ripple-based control with an excellent performance for load transients and reference voltage tracking because it exhibits a feedforward of the load current and the error of the output voltage. However, if V 2 I C is modulated with constant frequency, constant on-time or constant off-time, its dynamic response is hindered by delays in the response. This paper proposes a technique that synchronizes the clock of the converter to initialize the duty cycle when a worst-case load transient occurs using the current through the output capacitor to detect load transients. It is exemplified on a V 2 I c control but it is applicable to most of controllers as it only acts on the modulator.Index Terms-Clock synchronization, dynamic voltage scaling, load transient, point of load, V 2 I C .

<inline-formula><tex-math notation="LaTeX">$v^1$</tex-math></inline-formula> Concept: Designing a Voltage-Mode Control as Current Mode With Near Time-Optimal Response for Buck-Type Converters

“…3(b)]. The dynamic response can be further improved by synchronizing the modulator with the load step [8].…”

“…In [4] and [5], the inductor current is added to the v 2 control to stabilize it. On the other hand, Del Viejo et al [6] proposed in 2011, instead, to add the capacitor current information using only the output voltage, which allows the control to behave almost optimally under load transients [7], [8]. This control is named v 2 i c (or "current-mode control of the output capacitor current" in a previous version from 2010 [9]).…”

Overview, equivalences and design guidelines of v¹ concept: A voltage mode control that behaves as a current-mode with near time-optimal response

“…In [4,5], the inductor current is added to the v 2 control to stabilize it. On the other hand, [6], proposed in 2011, instead, to add the capacitor current information using only the output voltage, which allows the control to behave almost optimally under load transients [7,8]. This control is named v 2 i c (or "current-mode control of the output capacitor current" in a previous version from 2010 [9]).…”

Analysis of the effect of modulation delays on the size of the output capacitor

“…For example, if a loading transient occurs when the converter is in the off-time with constant switching frequency modulation, then the control needs to wait till the beginning of the next period to command an on-time because the modulation forces a constant period. The effect of this inherent delay of the modulation can be very dominant in the total voltage deviation and even shift the worst-case load transient from the unloading to the loading in applications with small duty cycle [6]. Therefore, the delays of the modulation affect the worst-case voltage deviation and, consequently, the minimum required size of the output capacitor to comply with dynamic requirements.…”

“…This paper studies the effect that different modulations have on the size of the output capacitor. It also shows a novel technique called "Clock Pulse Synchronization" based on the capacitor current (CPSI c ) in order to counteract the limitations of the modulator [6].…”