The Next Evolution of Digital Compensation Compensation-Free Point-of-Load Modules 10101010101 01010101010 10101010101 www.cui.com The Next Evolution of Digital Compensation Traditional power supplies and voltage regulators are able to produce stable output voltages due to the incorporation of control loops with negative feedback. A major challenge to properly implement negative feedback is to provide the correct frequency compensation associated with the feedback network. Initial implementations of voltage regulators employed analog circuitry for the control and feedback circuits. Later improvements in technology have allowed digital circuits to replace almost all of the analog functions in voltage regulators and power supplies. The incorporation of digital circuits has allowed the development of automatic compensation algorithms to ease the burden on the power design engineer. Auto-compensation is a great improvement over traditional topologies but still has some limitations due to the requirements of the circuits to determine the compensation parameters. Recent developments in digital voltage regulator controllers have created “compensation-free” topologies. These compensationfree designs provide superior voltage regulation while eliminating the issues associated with determining compensation parameters. ANALOG VOLTAGE REGULATORS Analog voltage regulators require the design engineer to determine the values for compensation resistors and capacitors and then to solder these components onto the PCB. The selection, placement and modification of the discrete compensation components adds delays and risks to power delivery designs. Some vendors simplify the compensation component selection process by allowing the user to select a single resistor and a single capacitor to compensate the regulator. While this option simplifies the user tasks, it reduces the probability that the resulting load current transient behavior of the power supply is acceptable. The design and implementation of analog voltage regulators is a manually-intensive process and thus carries undesirable risks and costs. Vin Error amplifier and gain stage FIGURE 1 Analog Switching Voltage Regulator Vref + Compensation Network FET Vout FET control L FET Attenuator Control Stage Power Stage page 2 Vin C Vin Error amplifier and gain stage www.cui.com The Next Evolution of Digital Compensation Vref + - FET Vout FET control Compensation Network ANALOG VOLTAGE REGULATORS WITH DIGITAL WRAPPERS Attenuator L FET C When an IC vendor adds a digital wrapper to an analog voltagePower regulator Control Stage Stagethere are benefits in the ability to configure, control and monitor some of the characteristics of the power supply. Selecting analog voltage regulators with digital wrappers improves upon the challenges and delays in designing with a traditional analog voltage regulator, but the risks and costs associated with the compensation components still exist. Vin Error amplifier and gain stage FIGURE 2 Analog Switching Voltage Regulator with ‘Digital Wrapper’ Vref User interface bus + - FET Compensation Network Limited digital configue, control and monitoring Vout FET control L FET C Attenuator Control Stage Power Stage DIGITAL VOLTAGE REGULATORS A digital voltage regulator topology can allow the user complete configurability, controllability and monitoring capability of the power supply via a software interface. Vin the user to Many digital voltage regulators are designed in a manner that allows select proportional, integral and derivative (PID) tap coefficients rather than physical compensation components to provide compensation for the voltage regulator feedback loop. With these topologies, the risks and delays of soldering (and unsoldering and then re-soldering) discrete compensationDigital resistors eliminated since the PID and and capacitors areFET mixed signal coefficients are entered and altered as software functions. The software compensation Vout FET Vref configure, L techniques reduce many of the delays and risks associated control with soldering components but control and the design engineer still needs to havemonitor extensive knowledge of compensation theory in FET C order to produce an optimized design. User interface bus page 3 Control Stage Power Stage configue, control and monitoring Attenuator Error amplifier and Control gainStage stage User interface bus The Next Evolution of Digital Compensation Limited digital configue, control and monitoring FIGURE 3 Digital Switching Voltage Regulator L FET Compensation Network C Attenuator Control Stage Vref Vout FET control + - Vref www.cui.com PowerFET Stage Power Stage Vin FET Digital and mixed signal configure, control and monitor Vout FET control L FET Vin C User interface bus Control Stage Digital and PowerFET Stage mixed signal configure, control and monitor Vref Vout FET control L FET C DIGITAL VOLTAGE REGULATORS User interface bus WITH AUTOMATIC COMPENSATION Stageinclude the incorporation Power Stage Recent advances in digital voltage Control regulators of an automatic Error Gain, the Kp need for the user to have knowledge and compensation topology that eliminates Signal experience in compensation techniques. These regulators are able to determine the optimum compensation (values for Kp , Ki and Kd ) for the circuit when power is applied to + the regulator or at any other time that a software to the unit re-calculate Integrator with command is sent Dutyto Cycle + the compensation. Automatic compensation risks and delays Gain, K i eliminates the costs, Signal associated + with topologies that require a design engineer to determine the compensation values. Differentiator with Gain, K d Gain, Kp Error Signal FIGURE 4 Digital PID Compensator Integrator with Gain, K i + + + Duty Cycle Signal Differentiator with Gain, K d page 4 Error Signal Fast Sampler Slow Sampler Gain Integator with Gain + + + - + Duty Cycle Reset with Gain - Duty Cycle Signal Vref www.cui.com FET Digital and mixed signal configure, control and monitor Vout FET control L FET The Next Evolution of Digital Compensation C User interface bus Control Stage Power Stage COMPENSATION EVOLVES AGAIN WITH COMPENSATION-FREE DESIGNS A superior digital voltage regulator topology to those that provide automatic compensation is one that requires no compensation at all. This is the promise of CUI’s NDM3Z-90 digital POL module, which is based on compensation-free technology. These modules determine the load current transient response by monitoring and adjusting the charge delivered to the load on a cycle-by-cycle basis. This technique allows the voltage regulator to optimize the load transient response each switching cycle of the regulator without Error Gain, Kp the use of feedback Signal loop compensation. The compensation-free topology is a superior technology due to the low latency involved in the load transient response. Low latency is achieved by the implementation of a faster Integrator withsignal path in+ the compensator Duty Cycle in addition + Gain,cycle-by-cycle Ki Signal to the traditional slower signal path. The charge delivery architecture also + incorporates non-linear transient response characteristics to provide superior output voltage regulation of the POL modules as compared to what could be achieved with more Differentiator One with benefit of low latency and non-linear conventional feedback loop compensation. Gain, K d transient response techniques is the reduction in output decoupling capacitors required. Decoupling capacitors provide transient control at frequencies above those to which the voltage regulator can respond. The low latency and non-linear transient response of the no compensation architecture extend the effective frequency range of the voltage regulator and thus minimize the number, area and cost of the decoupling capacitors required to achieve the desired transient response of the digital POL module. FIGURE 5 Compensation-Free Digital Compensator page 5 Error Signal Fast Sampler Slow Sampler Gain Integator with Gain + + + - + Duty Cycle Reset with Gain - Duty Cycle Signal www.cui.com The Next Evolution of Digital Compensation SUPERIOR POWER DELIVERY SOLUTIONS WITHOUT POWER SUPPLY EXPERTISE Compensation techniques have come a long way since the days of the manual “trial and error” methods employed in purely analog designs. The complexities of powering today’s advanced semiconductors coupled with increasingly short design cycles has driven an evolution in compensation methods. The latest compensation technology employed in many CUI’s Novum® digital power modules, coupled with an easy-to-use Novum Ace TM GUI (Graphical User Interface) also supplied by CUI, allows for rapid design cycles without the need for advanced power supply knowledge. Compensation-Free POL Modules NDM3Z-90 Learn More www.cui.com 20050 SW 112th Ave. Tualatin, Oregon 97062 page 6 ©CUI Inc 2016. All rights reserved. 04/2016