Digital controller design for point-of-load DC-DC converters with variable switching frequency

Abstract

Presented is a digital controller to regulate a point-of-load Buck converter. The regulator varies both the duty cycle, as well as the switching frequency, by controlling not only the on-time, but also the off-time of the switching period. The multi-loop digital controller, which achieves a tight voltage regulation and an excellent dynamic performance, is presented and its effectiveness is proven by means of experimental results. The controller architecture, together with an analogue-todigital converter, has been integrated in a 0.13 mm CMOS technology.Introduction: Regulation techniques for power-management units (PMUs) are gaining more and more importance in the research community, as well as for industrial products. In the field of point-of-load (PoL) converters, more and more digital controller implementations are emerging, since they are capable of realising configurable and high performance control algorithms [1][2][3][4]. Furthermore, digital CMOS implementations inherently profit from technology scaling, besides the significant advantage that such circuits can be easily incorporated in complex system-on-chip (SoC) solutions.In this Letter, a novel voltage-mode controller architecture, which has been implemented in a 0.13 mm CMOS technology, is presented. The controller regulates both the on-phase time and the switching frequency of the digital pulse-width modulated (DPWM) signal. The former is contolled by a classical proportional-integral-derivative (PID) structure. The switching frequency is appropriately chosen by a second, faster control loop. This ensures a tighter voltage regulation and avoids overreaction of the PID controller.

Modeling, Control, and Implementation of DC–DC Converters for Variable Frequency Operation

“…where x ∈ R n×1 , u ∈ R m ×1 , and y ∈ R p×1 define the states, inputs and outputs of the system, whereas switch configuration of the dc-dc converter can now be found, such that i = 1 for the configuration during the on-time, whereas i = 2 during the off-time. In contrast to [18] and [19], where (2) has been used as the starting point, here, (3) is substituted in the derivation of the averaged model, such that a more generalized model is acquired. The state-space equations representing the averaged system are then given by…”

“…Both the on-time and the off-time are modulated by the controller, yielding a variable frequency operation. A similar multiloop PID controller has been proposed by the authors in [18] and experimental results have been presented in [19], where in the previous publications, the switching period has been directly introduced as an additional control input. In the current study, a more flexible and generalized approach is presented, with the on-time and the off-time of the switching period as control inputs.…”

One‐comparator counter‐based controller for synchronous DC/DC converters

“…It is assumed that the counter has a very high resolution and that the clock period is much smaller than the settling time of the DC/DC converter. The counter in this case can still be modelled as an integrator according to (8); however, it is now followed by a quantiser block with a quantisation interval equal to the resolution of the PWM generator Δ P . The resolution of the PWM generator Δ P is generally equal or smaller than ΔD, therefore in this case…”

“…[1] classified controllers for DC/DC converters into five groups; hysteresis controllers [2][3][4][5][6][7], linear controllers in their digital form such as voltage-mode [8][9][10] or current-mode controllers [9,[11][12][13][14] and the classical PID controller [15][16][17][18][19][20][21][22][23], fuzzy-logic controllers [24][25][26][27], sliding-mode controllers [10,[28][29][30][31], predictive controllers [32][33][34][35][36][37][38] and other advanced controllers [39][40][41][42][43]. All of these controllers have been tested and demonstrated to provide precise control, excellent performance and robustness.…”

A self-calibration scheme for improved current share of multiphase DC-DC converter

“…The gain function is given by Eq. (8) [15][16]. In this paper, the digital voltage mode control is based on [17][18][19][20] for implemented into this control scheme.…”