Patent Publication Number: US-2003222628-A1

Title: Auxiliary boundary regulator that provides enhanced transient response

Description:
FIELD OF THE INVENTION  
       [0001] This invention generally relates to electronic systems and in particular it relates to an auxiliary boundary regulator that provides enhanced transient response.  
       BACKGROUND OF THE INVENTION  
       [0002] There are a number of ways to accomplish a voltage regulation function, but two are more commonly used: (1) a continuous-time analog regulator or switched mode power supply (SMPS) with a continuous-time control loop, and (2) a ‘hysteretic’ type of converter which simply responds to provide energy when the regulated output falls outside of a hysteretic window. The first type provides a tightly controlled, low-ripple, output voltage, and in the case of the SMPS, a controlled operating frequency, but the transient response time is slow. A fast load or supply transient can send the output out of regulation limits before the control loop can respond. The second type has a large ripple voltage and uncontrolled frequency, but the response time is extremely fast.  
       [0003] One prior art device involves the use of a linear regulator to perform the boundary function about an SMPS main converter. Another prior art device involves using a similar fast recovery converter around the main converter, which is an SMPS.  
       SUMMARY OF THE INVENTION  
       [0004] A regulator circuit with an auxiliary boundary regulator that provides enhanced transient response includes: an upper comparator having a first input coupled to a feedback node and a second input coupled to a first reference voltage node; a lower comparator having a first input coupled to the feedback node and a second input coupled to a second reference voltage node; a first switching device having a control node coupled to an output of the upper comparator; a second switching device having a control node coupled to an output of the lower comparator; an inductor having a first end coupled to the first and second switching devices, and a second end coupled to an output node; and a feedback circuit coupled between the output node and the feedback node. This circuit provides a precise, quiet, linear regulator that provides a tightly regulated output with a fast regulator working in parallel to ensure that the output voltage stays within an acceptable boundary.  
     
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
     [0005] In the drawings:  
     [0006]FIG. 1 is a schematic circuit diagram of a preferred embodiment device with an auxiliary boundary regulator that provides enhanced transient response;  
     [0007]FIG. 2 is a diagram describing the operation of the circuit of FIG. 1.  
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS  
     [0008] The preferred embodiment device shown in FIG. 1 provides a precise, quiet, linear regulator to provide a tightly regulated output, but with a fast regulator working in parallel to ensure that the output voltage stays within an acceptable boundary. The device also integrates the boundary regulation function with the main continuous time function, using the same switching MOSFETs for both functions. In this way, the fast response of the boundary regulation is added without the expense of an extra pair of MOSFETs or an extra inductor.  
     [0009] The preferred embodiment device of FIG. 1 includes: main regulator  20 ; boundary regulatory  22  that includes upper comparator  24 , lower comparator  26 , transistors  28  and  30 , lower threshold voltage source V_LOW, and upper threshold voltage source V_HIGH; feedback resistors  32  and  34 ; inductor  36 ; load resistance  38 ; capacitor  40 ; output voltage Vout; supply voltage V_SUPPLY; and reference voltage VREF.  
     [0010] In the diagram shown in FIG. 2, the main regulator  20  provides a regulation point shown by the line labeled “Regulation”. The boundary regulator  22  simply consists of a pair of comparators  24  and  26  with thresholds V_LOW and V_HIGH set at some voltage above “Upper Boundary” and below, “Lower Boundary”, the regulation point.  
     [0011] The boundary regulator  22  remains off unless a transient presents itself of a magnitude sufficient to displace the output voltage Vout from the regulation line into the Boundary Regulator Active areas. Once the output Vout exceeds the upper or lower boundaries, the boundary regulator  22  will activate and provide counteractive energy until such time as the output voltage Vout returns to a point within the two boundary limits.  
     [0012] While this invention has been described with reference to an illustrative embodiment, this description is not intended to be construed in a limiting sense. Various modifications and combinations of the illustrative embodiment, as well as other embodiments of the invention, will be apparent to persons skilled in the art upon reference to the description. It is therefore intended that the appended claims encompass any such modifications or embodiments.