Design of an integrated single-input dual-output 3-switch buck converter based on sliding mode control

Abstract

This paper presents the design, implementation, and testing of a proof-of-concept monolithic single-input dual-output buck converter. The proposed architecture implements an analog hysteretic controller. This avoids the use of extra circuitry to generate a dedicated reference carrier signal to create the pulse-width modulated waveform, thus saving area, and reducing static power consumption. Furthermore, the proposed topology implements only three switches (instead of four switches in conventional solutions), and can save additional silicon area with proper design of the power switches in the voltage regulator. The IC prototype was fabricated in standard 0.5 μm CMOS technology (V_THN = 0.78 V, V_THP = −0.93 V), operates with a single voltage supply of 1.8 V, generates 1.2 and 0.9 V output-voltage levels, and supplies a maximum total current of 200 mA (100 mA provided by each output), reaching up to 88 % efficiency.

Appendix 1 sliding mode controller

In this appendix, the general form of the switching function in a SMC for asymptotic tracking is discussed [11]. The SMC can be derived if the system is expressed in its controllable canonical form

$$ \begin{array}{cc} {\dot{e}}_{a}(t) &= e_b(t) \\{\dot{e}}_{b}(t) &= e_c(t) \\ \vdots & \vdots \\ {\dot{e}}_{\rho-1}(t)&= e_{\rho}(t) \end{array} $$

(12)

where e_a is the error function, e_ρ is the control input, and ρ is the order of the system to be controlled. The control input in Eq. (13) is the linear combination of all state canonical state variables where its coefficients are chosen in such way that the polynomial expressed in Eq. (14) meets the Hurwitz criterion, i.e. all its roots have negative real part.

$$ e_{\rho} = -(k_ae_a + k_be_b + \cdots + k_{\rho - 1}e_{\rho - 1}) $$

(13)

$$ P(s) = s^{\rho - 1} + k_{\rho - 1}s^{\rho - 2} + \cdots + k_{a} $$

(14)

The switching function in Eq. (15) represents the (ρ − 1) dimensional surface where the points of discontinuity merge.

$$ s(e_{a}, t) = (k_{a}e_{a} + k_{b}e_{b} + \cdots + k_{\rho - 1}e_{\rho - 1}) + e_{\rho} = 0 $$

(15)

For the particular case of ρ = 2, Eq. (15) simply becomes Eqs. (5) and (6).