Peak-buck peak-boost current-mode control for switched step-up step-down regulators

Abstract

A peak-buck peak-boost current mode control structure and scheme for a synchronous four-switch and non-synchronous two-switch buck-boost regulators sense input and output voltages to smoothly transition between buck mode, buck-boost mode, and boost mode for high power efficiency and low output ripples. With the inductor current sensing, the control scheme achieves the best performance in continuous conduction and discontinuous condition mode operations.

We claim: 
     
         1 . A peak-buck peak-boost control circuit for a voltage regulator capable of being configured as a buck regulator, a buck-boost regulator or a boost regulator, the buck-boost regulator receiving an input voltage and providing an output voltage. 
     
     
         2 . The peak-buck peak-boost control circuit of  claim 1 , comprising:
 a mode selection circuit generating control signals representing (a) a first control state in which the input voltage is greater than the output voltage by at least a predetermined value; (b) a second control state in which the input voltage is greater than the output voltage less than or equal to the predetermined value; (c) a third control state in which the output voltage is greater than the input voltage by less than or equal to a second predetermined value; (d) a fourth control state in which the output voltage is greater than the input voltage by at least the predetermined value; and   a switch control signal generation circuit for generating control signals for operating switches in the voltage regulator, such that the voltage regulator is configured as (a) a buck regulator in the first control state, (b) a buck-boost regulator in the second and third control states, and (c) a boost regulator in the fourth control state.   
     
     
         3 . The peak-buck peak-boost control circuit of  claim 2 , wherein the mode selection circuit incorporates hysteresis for transitioning between the first and second control states, or for transitioning between the third and fourth control states. 
     
     
         4 . The peak-buck peak-boost control circuit of  claim 2 , wherein the output voltage is provided as a scaled feedback signal. 
     
     
         5 . The peak-buck peak-boost control circuit of  claim 2 , wherein the voltage regulator comprises an inductor and wherein the switch control signal generation circuit includes a signal generator that provides a ramping voltage signal and a current sense amplifier that determines a peak value in a current flowing in the inductor. 
     
     
         6 . The peak-buck peak-boost control circuit of  claim 5 , wherein the ramping voltage signal comprises a linear segment. 
     
     
         7 . The peak-buck peak-boost control circuit of  claim 5 , wherein the current flowing in the inductor is determined from a voltage across a sense resistor. 
     
     
         8 . The peak-buck peak-boost control circuit of  claim 5 , wherein the switch control signal generation circuit comprises a first comparator that determines an occurrence of the peak value using the ramping voltage, the inductor current, and an error signal derived from the output voltage. 
     
     
         9 . The peak-buck peak-boost control circuit of  claim 8 , wherein the first comparator controls switches in an output side of the voltage regulator. 
     
     
         10 . The peak-buck peak-boost control circuit of  claim 9  wherein, when in either the third control state or the fourth control state, in response to the occurrence of the peak value, the switch control signal generation circuit closes a switch connecting the inductor from an output terminal of the voltage regulator and opens a switch connecting the inductor to a ground reference. 
     
     
         11 . The peak-buck peak boost control circuit of  claim 10  wherein, in the third control state, at a predetermined time following the occurrence of the peak value, the switch control signal generation circuit opens a switch connecting the inductor from an input terminal of the voltage regulator and closes a switch connecting the inductor to a ground reference. 
     
     
         12 . The peak-buck peak-boost control circuit of  claim 8 , wherein the error signal is an amplified difference between a reference voltage and the output voltage. 
     
     
         13 . The peak-buck peak-boost control circuit of  claim 8 , further comprising a compensation circuit receiving the error signal for providing loop stability in the voltage regulator. 
     
     
         14 . The peak-buck peak-boost control circuit of  claim 5 , wherein the switch control signal generation circuit comprises a second comparator that determines an occurrence of the peak current using the ramping voltage, the inductor current, an offset voltage and an error signal derived from the output voltage. 
     
     
         15 . The peak-buck peak-boost control circuit of  claim 14 , wherein the offset voltage is derived from a difference in voltage at two time points of the ramping voltage. 
     
     
         16 . The peak-buck peak-boost control circuit of  claim 15 , wherein the two time points are specific time points within a switching cycle of the peak-buck peak-boost control circuit. 
     
     
         17 . The peak-buck peak-boost control circuit of  claim 14 , wherein the comparator controls switches in an input side of the voltage regulator. 
     
     
         18 . The peak-buck peak-boost control circuit of  claim 17  wherein, when in either the first control state or the second control state, in response to the occurrence of the peak value, the switch control signal generation circuit opens a switch connecting the inductor from an input terminal of the voltage regulator and closes a switch connecting the inductor to a ground reference. 
     
     
         19 . The peak-buck peak boost control circuit of  claim 18  wherein, in the second control state, at a predetermined time, the switch control signal generation circuit closes a switch connecting the inductor from an output terminal of the voltage regulator and opens a switch connecting the inductor to a ground reference. 
     
     
         20 . In a voltage regulator capable of being configured as a buck regulator, a buck-boost regulator or a boost regulator, the buck-boost regulator receiving an input voltage and providing an output voltage, a method for controlling the voltage regulator comprising:
 selecting a mode of operation based on determining (a) a first control state in which the input voltage is greater than the output voltage by at least a predetermined value; (b) a second control state in which the input voltage is greater than the output voltage less than or equal to the predetermined value; (c) a third control state in which the output voltage is greater than the input voltage by less than or equal to a second predetermined value; (d) a fourth control state in which the output voltage is greater than the input voltage by at least the predetermined value; and   generating switch control signals for operating switches in the voltage regulator, such that the voltage regulator is configured as (a) a buck regulator in the first control state, (b) a buck-boost regulator in the second and third control states, and (c) a boost regulator in the fourth control state.   
     
     
         21 . The method of  claim 20 , wherein selecting the mode of operation further comprises incorporating hysteresis for transitioning between the first and second control states, or for transitioning between the third and fourth control states. 
     
     
         22 . The method of  claim 20 , wherein the output voltage is provided as a scaled feedback signal. 
     
     
         23 . The method of  claim 20 , wherein the voltage regulator comprises an inductor and wherein generating the switch control signals includes using a ramping voltage signal to determine a peak value in a current flowing in the inductor. 
     
     
         24 . The method of  claim 23 , wherein the ramping voltage signal comprises a linear segment. 
     
     
         25 . The method of  claim 23 , wherein the current flowing in the inductor is determined from a voltage across a sense resistor. 
     
     
         26 . The method of  claim 23 , wherein generating the switch control signals comprises determining an occurrence of the peak value using the ramping voltage, the inductor current, and an error signal derived from the output voltage. 
     
     
         27 . The method of  claim 26 , wherein the occurrence of the peak value determines switching in switches in an output side of the voltage regulator. 
     
     
         28 . The method of  claim 27  further comprising, when in either the third control state or the fourth control state, in response to the occurrence of the peak value, closing a switch that connects the inductor from an output terminal of the voltage regulator and opening a switch that connects the inductor to a ground reference. 
     
     
         29 . The method of  claim 28  further comprising, in the third control state, at a predetermined time following the occurrence of the peak value, opening a switch that connects the inductor from an input terminal of the voltage regulator and closing a switch that connects the inductor to a ground reference. 
     
     
         30 . The method of  claim 26 , wherein the error signal is an amplified difference between a reference voltage and the output voltage. 
     
     
         31 . The method of  claim 26 , further comprising compensating for loop stability in the voltage regulator using the error signal. 
     
     
         32 . The method of  claim 23 , wherein generating the switch control signals comprises determining an occurrence of the peak current using the ramping voltage, the inductor current, an offset voltage and an error signal derived from the output voltage. 
     
     
         33 . The method of  claim 32 , wherein the offset voltage is derived from a difference in voltage at two time points of the ramping voltage. 
     
     
         34 . The method of  claim 33 , wherein the two time points are specific time points within a switching cycle of the control method. 
     
     
         35 . The method circuit of  claim 33 , wherein the occurrence of the peak current controls switching in switches in an input side of the voltage regulator. 
     
     
         36 . The method of  claim 35  further comprising, when in either the first control state or the second control state, in response to the occurrence of the peak value, opening a switch that connects the inductor from an input terminal of the voltage regulator and closing a switch that connects the inductor to a ground reference. 
     
     
         37 . The peak-buck peak boost control circuit of  claim 36  further comprising, in the second control state, at a predetermined time, the switch control signal generation circuit closing a switch that connects the inductor from an output terminal of the voltage regulator and opening a switch that connects the inductor to a ground reference.