Compensation Methods in Voltage Regulators
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Compensation Methods in Voltage Regulators



Feedback signals are used in voltage regulator circuits in order to produce a ...

Feedback signals are used in voltage regulator circuits in order to produce a
controlled output voltage. When properly implemented, feedback will improve
the performance of the circuit. A major contributor to proper implementation of a
feedback circuit is the compensation network. This article will give an overview of
some methods used to implement compensation in voltage regulators including techniques for automatic digital compensation.

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Compensation Methods in Voltage Regulators Compensation Methods in Voltage Regulators Document Transcript

  • Compensation Methodsin Voltage RegulatorsAn Evolution from Analog to DigitalBy Bruce Rose, Technical Marketing Manager, CUI Inc
  • Compensation Methodsin Voltage RegulatorsFeedback signals are used in voltage regulator circuits in order to produce acontrolled output voltage. When properly implemented, feedback will improvethe performance of the circuit. A major contributor to proper implementation of afeedback circuit is the compensation network. This article will give an overview ofsome methods used to implement compensation in voltage regulators includingtechniques for automatic digital compensation.The Automotive AnalogyAn analogy to assist in understanding compensation by the switching regulator. The control stage consistsin voltage regulators lies in the suspension system of an attenuator, an error amplifier, a gain circuit andof an automobile. Operators of cars desire different a compensation circuit. The switching regulator canstyles of rides depending upon the use of the car. either be built with discrete components solderedRiders in limousines would like to enjoy a smooth directly to the host circuit board or obtained fromride and not notice any external disturbances. At the manufacturers that offer voltage regulator Point ofother extreme, race car drivers would like their cars Load (POL) modules with the components placedto respond quickly to the external forces of starting, on a daughter circuit board which is then connectedstopping and turning. While both of these styles of to the host circuit board. Some advantages of POLcars may experience similar disturbances, different modules are that much of the voltage regulatorreactions of the cars to the disturbances are desired. circuit design has been done by the module vendorAs a result, the suspension systems of the cars are and the modules can occupy less space on the hosttuned to react in the desired manner to specific board than would a discrete solution.disturbances. A properly tuned suspension systemwill give the car its desired ride qualities. Tuning Vinthe suspension of a car is similar to adjusting thefeedback compensation circuit of a voltage regulator. Error amplifier and gain stage FET VoutSwitching Regulators Vref + FET control L -In order to achieve good power conversion efficiency, Compensation FET Cdesign engineers often employ switching regulators Network(figure 1). Typical switching regulators consist of Attenuatortwo primary functional blocks; a power stage and a Control Stage Power Stagecontrol stage. The power stage conducts the currentflow in the voltage regulator. It contains switching Figure 1 Analog Switching Voltage RegulatorFETs (Field Effect Transistors), a circuit to controlthe switching of the FETs and an output filter which Vinincludes inductance and capacitance. The controlstage provides the signals to the power stage suchthat the desired output voltage waveform is produced Error amplifier and gain stage FET Vout Vref + FET L controlpage 2 User interface - bus Compensation FET C Network Limited digital configue, control Attenuator and monitoring Control Stage Power Stage
  • Compensation Methodsin Voltage RegulatorsCompensating Analog Voltage RegulatorsIn most analog switching regulators, internal nodes implemented or a POL module based upon an analogare brought external to the circuit so that the user switching regulator is used.can select the circuit compensation components.This external compensation feature allows the One can think of the design of the analog switchinguser to optimize the performance of the switching regulator as a similar process to purchasing a kit carregulator for their application. Optimizing the voltage and then selecting and installing all of the suspensionregulator transient response involves measuring or components. It takes specific tools, knowledge andmodeling the circuit and then calculating the values experience to properly tune the suspension of a car.of the compensation components. The circuit is Adjusting the suspension in the car posses risks,then modeled or measured with the compensation including damaging the car while driving it with acomponents installed. This process is often repeated poorly-tuned suspension, or breaking componentsmany times until the desired result is achieved. while making suspension adjustments. In either case,Optimizing the compensation of a digital switching time and resources will be required to repair theregulator is accomplished in a similar manner; damage caused while tuning the suspension.however changes are made using firmware rather Vinthan physical components. As a result of the increasing number of digital systems being implemented in today’s designs, voltageProper implementation of the compensation network regulator vendors are now offering analog switching Error amplifier and gain stagewithin an analog switching regulator requires regulators with ‘digital wrappers’FET (figure 2). The Voutengineers with special tools, skills and experience. voltage regulator portions of these circuits are very Vref + FET control L -If an analog switching regulator is measured during similar to the traditional analog switching regulators. FET Cthe compensation design phase, then the circuit The digitalCompensation enables the system to employ wrapper Networkboard needs to be re-soldered many times. If the software to implement Configure, Control and Monitorcircuit is modeled and not measured, there is still (CCM) functions of the voltage regulator, in a limited Attenuatorthe need to eventually solder together a physical manner. Control Stage to use CCM Power Stage in a voltage The ability functionscircuit to measure the performance. The process regulator via software control is of benefit to theof re-soldering the compensation components design team during the development phase and to theintroduces a substantial level of risk to the design user of the final product.process. It is common that the wrong value of a Vincompensation component is installed, another partof the circuit is accidently modified, or the circuit Error amplifier andboard is damaged during the design process. It gain stage FET Voutis also possible that the circuits drawing power Vref + FET L controlfrom the voltage regulator can become damaged interface User -due to improper compensation of the voltage bus Compensation FET C Networkregulator. When any of these events occur, time Limited digitaldelays and expenses are incurred to recognize the configue, control Attenuator and monitoringproblem, identify a solution to the problem, and Control Stage Power Stageimplement the repair. The above mentioned risks,procedures and required resources exist whether adiscrete design of an analog switching regulator is Figure 2 Analog Switching Voltage Regulator with ‘Digital Wrapper’page 3 Vin Digital and FET mixed signal Vout Vref configure, FET L control and control
  • Compensation Methods in Voltage Regulators Vin engineers (figure 3), providing superior performance Analog switching regulators with digital wrappers to earlier topologies. Similar to analog switching are being offered to design engineers for discrete regulators, digital regulators require a control designs andamplifier and modules. Some module vendors Error as POL gain stage FET circuit and a power stage. The power stage for a have chosen to include most of the compensation Vout digital switching regulator is similar to that for Vref + FET L components internal to the module. The module - control an analog switching regulator. The control circuit user is then provided a single internal compensation Compensation FET C in a digital regulator is implemented with digital node and is required to select only one resistor and Network and mixed-signal circuits. An advantage of this one capacitor to adjust the performance of the topology is that extensive CCM functions can be Attenuator module. The advantage of this process is that tuning implemented. The extensive set of CCM functions in Control Stage Power Stage the performance of the module is simpler than a digital voltage regulator provides greater benefit when the user must select all of the compensation than the limited CCM functions present in an analog components. A trade-off of this compensation switcher with a digital wrapper. Another advantage technique is that the user is not able to select the of digital switching regulators is that optimizing the Vin complete set of compensation network components. performance of the circuit can be accomplished The ability to select all of the compensation more easily and automatically. components would enable greater optimization of the Error amplifier and gain stage FET performance of the voltage regulator. The ability to Vout The compensation function in a digital voltage select Vref only+a single resistor and capacitor is similar FET control L regulator can be implemented as Proportional, User -interface bus to selecting the shock absorbers for a car, but not Integral, Differential (PID) taps, which are coefficients Compensation FET C being allowed to tune any other component in the Network used in the digital control circuit to define the Limitedsuspension system. digital response of the voltage regulator. An advantage configue, control and monitoring Attenuator of using firmware PID taps is that the designer Compensating Digital Voltage Regulators Control Stage Power Stage can configure and control the performance of the voltage regulator with software. An infinite number of The technical evolution of voltage regulators started changes can be made to the response characteristics with analog switching topologies for increased of the circuit without risk of damaging components efficiency, transitioning to the addition of digital or the circuit board. In addition, the behavior of the wrappers for limited CCM functions. Today digital system can be monitored and the performance of the switching voltage regulators are available to design voltage regulator circuit can be re-tuned throughout Vin the life of the product. This ability to easily modify the performance of the voltage regulator is similar to push-button suspension tuning which is available in Digital and FET some cars. mixed signal Vout Vref configure, FET L control and control monitor Auto Compensation FET C Some advanced digital regulator controllers User interface bus offer the ability to automatically compensate the regulator for optimum performance by monitoring Control Stage Power Stage the characteristics of the output voltage waveform. One advantage of automatic compensation Bild 3 Digital Switching Voltage Regulator is that the circuit designer does not need any page 4
  • Compensation Methodsin Voltage Regulatorsspecial tools, knowledge or experience to optimize to operate at optimum performance. All of thesethe performance of the voltage regulator. In a topologies traditionally require a design team withregulator with analog compensation components, special tools, knowledge and experience in powerthe compensation must be set such that the supply design to create an acceptable solution. Theoutput voltage characteristics are acceptable over multiple families of digital POL modules from CUI’schanges due to initial component tolerances, aging, Novum® Advanced Power line incorporate automatictemperature, input voltage and many other factors. compensation, allowing system designers ease ofThis means that the circuit is never operating at use and superior performance in nextgenerationthe optimum performance point. Digital voltage applications.regulators with automatic compensation enable thevoltage regulator to operate at peak performance For more information visit of changes in the system. Automaticcompensation of digital voltage regulators can bethought of as having an expert mechanic alwaysin the car to optimize the ride without any burdenon the driver or passengers. CUI Inc is the only POLmodule manufacturer in the industry to offer multiplefamilies of commercially available digital voltageregulator modules with automatic compensation.Proper compensation of voltage regulators enablesusers to realize optimum performance from theircircuits. Tuning the performance of a circuit usingtraditional analog switching regulators involves asubstantial level of risk. Vendors of some analogvoltage regulator-based POL modules offer productsthat simplify the task of compensation by limitingthe choices available to the user. Digital voltageregulators, on the other hand, enable firmware basedCCM functions which permit the voltage regulator 20050 SW 112th Ave. Tualatin, Oregon 97062 11/2012 ©CUI Inc 2012. All rights reserved. Solus and Novum are trademarks of CUI Inc. Other namespage 5 and brands are the property of their respective owners.