SUPPLY WITH A SERIAL COMMUNICATIONS INTERFACE y RELATED PATENT APPLICATIONS

This application claims priority to commonly owned United States Provisional Patent

Application Serial Number 61/419,593; filed December 3, 2010; entitled "User-Configurable, Calibrated Sensorless Efficiency-Optimizing, Power/Energy Conversion Switch-Mode Power Supply with a Serial Communications Interface," by Terry Cleveland, Clifford Ellison III, Scott Dearborn and Keith Pazul; and is related to commonly owned United States Patent Application Serial Number ; filed , 2011; entitled "Lossless Inductor

Current Sensing in a Switch-Mode Power Supply," by Scott Dearborn; United States Patent Application Serial Number ; filed , 2011; entitled "User- Configurable, Efficiency-Optimizing, Calibrated Sensorless Power/Energy Conversion in a Switch-Mode Power Supply," by Terry Cleveland, Clifford Ellison III, Scott Dearborn and Keith Pazul; and United States Patent Application Serial Number ; filed

, 201 1 ; entitled "User-Configurable, Efficiency-Optimizing, Power/Energy

Conversion in a Switch-Mode Power Supply With Serial Communications Interface," by Terry Cleveland, Clifford Ellison III, Scott Dearborn and Keith Pazul; all of which are hereby incorporated by reference herein for all purposes.

TECHNICAL FIELD

The present disclosure relates to switch mode power supplies, and, more particularly, to efficiency-optimizing, calibrated sensorless power/energy conversion in a switch-mode power supply (SMPS).

BACKGROUND

The synchronous buck switch-mode power converter is a commonly used topology for switch-mode power supply (SMPS) applications. The SMPS topology is gaining wider acceptance because of its high efficiency, small size and light weight. However, as the size of an SMPS is decreased, heat dissipation/removal therefrom becomes more problematic. Even though the typical efficiency of an SMPS may be 90 percent, there still remains 10 percent of the energy used by the SMPS becoming wasted heat. In addition, the high efficiency of the SMPS is optimized for only a single load condition. However, in real world applications power utilization loads vary over a wide range, and so do the associated SMPS efficiencies at those loads. Current sensing in the SMPS topology can be challenging and must be overcome in design. Knowing or monitoring the current being injected into the load provides protection for the power converter and can improve dynamic performance during closed loop control thereof.

Inductors in the SMPS are used to store energy during a portion of the switching cycle. The electrical characteristics, e.g., inductance and magnetic saturation values, of the SMPS inductor may vary widely. The tolerance of the inductor characteristics varies with temperature and/or voltage, so SMPS systems must be "over-designed" to optimize SMPS system efficiency for worst case conditions. Also, accurate measurement of the inductor current from one SMPS to another and at different load currents becomes problematic. Having the ability to accurately calibrate inductor current sense circuits associated with the inductors of a multiphase SMPS system would improve the dynamic performance and eliminate hot spots for the multiple phase converters of the multiphase SMPS system. In addition, having the ability to communicate with the SMPS system allows for operating parameters to be monitored, diagnostics to be performed, and operating objectives to be altered.

SUMMARY

Therefore a need exists for a higher performance power/energy conversion switch- mode power supply (SMPS) that maintains improved efficiencies for substantially all load conditions, and is able to communicate with a host system so that operating parameters can be monitored, diagnostics can be performed, and operating objectives can be altered in the SMPS. This may be accomplished with an intelligent pulse width modulation (PWM) controller that adapts the SMPS system operating parameters to optimize efficiency, remove hot spots and isolate faults by integrating a microcontroller, a serial communications interface, PWM digital circuits and analog circuits into a single integrated circuit, thereby reducing the number of external connections, silicon die area and integrated circuit packages then have been required by prior technology SMPS systems. Thereby allowing smaller printed circuit board space and fewer external components that result in lower cost to manufacture and improved reliability and flexibility of the SMPS system. These improved efficiencies available for substantially all load conditions may be achieved by combining intelligent control and the use of pulse width modulation (PWM) with calibrated sensorless feedback techniques more fully described hereinafter. According to the teachings of this disclosure, the intelligent SMPS controller may be programmed to optimize SMPS efficiencies for all operating parameters, e.g., switching frequencies, delay time between switches, drive capabilities, etc. , over substantially all load conditions of the SMPS. Being able to communicate with the SMPS system allows for operating parameters to be monitored, diagnostics to be performed, and operating objectives to be altered.

According to a specific example embodiment of this disclosure, a switch-mode power supply (SMPS) comprises; at least one power switch coupled to a voltage source; a power inductor coupled to the at least one power switch; a filter capacitor coupled to a load side of the power inductor that provides a regulated voltage output of the SMPS; and a SMPS controller coupled to the voltage source, the at least one power switch, the power inductor and the regulated voltage output of the SMPS, wherein the SMPS controller comprises: at least one driver coupled to the at least one power switch; a pulse width modulation (PWM) generator having an output coupled to and controlling the at least one driver; a digital processor having a memory, the digital processor is coupled to and provides operating parameters to the PWM generator during operation thereof; a voltage comparison circuit for comparing the regulated output voltage to a reference voltage, wherein the voltage comparison circuit generates an error signal representative of a difference between the regulated output voltage and the reference voltage, and wherein the error signal is coupled to an error input of the PWM generator; a sensorless tunable complimentary filter coupled to the power inductor, wherein the sensorless tunable complimentary filter measures current through the power inductor and provides a voltage output to the digital processor that is representative of the current flowing through the power inductor, and a communications interface coupled to the digital processor for providing user-configurable operating parameters to the SMPS; wherein the digital processor optimizes operation of the SMPS by providing operating parameters to the SMPS controller for all operating conditions of the SMPS. According to another specific example embodiment of this disclosure, a method for user-configurable optimization of a switch-mode power supply (SMPS) operation comprises the steps of: providing at least one power switch coupled to a voltage source; providing a power inductor coupled to the at least one power switch; providing a filter capacitor coupled to a load side of the power inductor that provides a regulated voltage from the SMPS; and providing a SMPS controller, wherein the SMPS controller facilitates: coupling at least one driver to the at least one power switch, controlling the at least one driver with a pulse width modulation (PWM) generator, comparing the regulated voltage from the SMPS to a reference voltage with a voltage comparison circuit, generating a voltage error signal representative of a difference between the regulated voltage and the reference voltage with the voltage comparison circuit, coupling the voltage error signal to the PWM generator, measuring current through the power inductor with a sensorless tunable complimentary filter coupled to the power inductor; providing a current output signal representative of the current flowing through the power inductor with the sensorless tunable complimentary filter, providing a digital processor having a memory, wherein the voltage error signal and the current output signal are coupled to inputs of the digital processor and the digital processor controls the PWM generator for adjusting operating parameters based upon the current output and voltage error signals; and providing a communications interface coupled to the digital processor for supplying user-configurable operating parameters to the SMPS.

BRIEF DESCRIPTION OF THE DRAWINGS

A more complete understanding of the present disclosure thereof may be acquired by referring to the following description taken in conjunction with the accompanying drawings wherein:

Figure 1 illustrates a schematic block, diagram of a basic voltage regulator system;

Figure 2 illustrates a more detailed schematic block diagram of the voltage regulator system shown in Figure 1 ;

Figure 3 illustrates a schematic diagram of the power circuit shown in Figure 2 implemented as a switch-mode power supply (SMPS), according to a specific example embodiment of this disclosure;

Figure 4 illustrates a more detailed schematic block diagram of the control circuit shown in Figure 2, according to the specific example embodiment of this disclosure;

Figure 5 illustrates a schematic diagram of a circuit for losslessly measuring inductor current of a SMPS, according to a specific example embodiment of this disclosure; Figure 6 illustrates a schematic diagram of a circuit for losslessly measuring inductor current of a SMPS, according to another specific example embodiment of this disclosure;

Figure 7 illustrates a graph of pole frequency adjustments for the circuits shown in Figures 5 and 6;

Figure 8 illustrates a graph of DC gain adjustments for the circuits shown in Figures 5 and 6; and

Figure 9 illustrates a schematic block diagram of a mixed signal integrated circuit device for controlling a SMPS system using the specific example embodiments of the tunable complimentary filters shown in Figures 5 and 6.

While the present disclosure is susceptible to various modifications and alternative forms, specific example embodiments thereof have been shown in the drawings and are herein described in detail. It should be understood, however, that the description herein of specific example embodiments is not intended to limit the disclosure to the particular forms disclosed herein, but on the contrary, this disclosure is to cover all modifications and equivalents as defined by the appended claims.

DETAILED DESCRIPTION

Referring now to the drawing, the details of specific example embodiments are schematically illustrated. Like elements in the drawings will be represented by like numbers, and similar elements will be represented by like numbers with a different lower case letter suffix.

, In a general sense, a power converter can be defined as a device which converts one form of energy into another on a continuous basis. Any storage or loss of energy within such a power system while it is performing its conversion function is usually identical to the process of energy translation. There are many types of devices which can provide such a function with varying degrees of cost, reliability, complexity, and efficiency.

The mechanisms for power conversion can take many basic forms, such as those which are mechanical, electrical, or chemical processing in nature. The focus herein will be on power converters which perform energy translation electrically and in a dynamic fashion, employing a restricted set of components which include inductors, capacitors, transformers, switches and resistors. How these circuit components are connected is determined by the desired power translation. Resistors introduce undesirable power loss. Since high efficiency is usually an overriding requirement in most applications, resistive circuit elements should be avoided or minimized in a main power control path. Only on rare occasions and for very specific reasons are power consuming resistances introduced into the main power control path. In auxiliary circuits, such as sequence, monitor, and control electronics of total system, high value resistors are common place, since their loss contributions are usually insignificant.

Referring to Figure 1, depicted is a schematic block diagram of a basic voltage regulator system. A power system 102, e.g., a basic switch-mode power converter where an input of an uncontrolled source of voltage (or current, or power) is applied to the input of the power system 102 with the expectation that the voltage (or current, or power) at the output will be very well controlled. The basis of controlling the output is to compare it to some form of reference, and any deviation between the output and the reference becomes an error. In a feedback-controlled system, negative feedback is used to reduce this error to an acceptable value, as close to zero as is required by the system. It is desirable, typically, to reduce the error quickly, but inherent with feedback control is the trade-off between system response and system stability. The more responsive the feedback network is, the greater becomes the risk of instability.

At this point, it should be mentioned that there is another method of control - feed forward. With feed forward control, a control signal is developed directly in response to an input variation or perturbation. Feed forward is less accurate than feedback since output sensing is not involved, however, there is no delay waiting for an output error signal to be developed, and feed forward control cannot cause instability. It should be clear that feed forward control typically is not adequate as the only control method for a voltage regulator, but it is often used together with feedback to improve a regulator's response to dynamic input variations.

Referring to Figure 2, depicted is a more detailed schematic block diagram of the voltage regulator system shown in Figure 1. The power system 102 has been separated into two blocks: the power circuit 206 and the control circuit 208. The power circuit 206 handles the power system load current and is typically large, robust, and subject to wide temperature fluctuations. Its switching functions are by definition, large-signal phenomenon, normally simulated in most stability analyses as just a two-state switch with a duty cycle. The output filter (not shown) is also considered as a part of the power circuit 206, but can be considered as a linear block. The control circuit 208 will normally be made up of a gain block, an error amplifier, and a pulse-width modulator, used to define the duty cycle for the power switches. According to the teachings of this disclosure, the control circuit 208 is optimized to respond to disturbances in the power system 102 while maintaining a desired output voltage, VOUT-

Referring to Figure 3, depicted is a schematic diagram of the power circuit shown in Figure 2 implemented as a switch-mode power supply (SMPS), according to a specific example embodiment of this disclosure. The power circuit 206 of the SMPS may comprise a power source 320, e.g., battery, a power inductor 312, high and low switches 316 and 318, respectively, e.g., power field effect transistors; a load capacitor 310 for smoothing alternating current (AC) ripple from the desired direct current (DC) output, and a boot voltage capacitor 314. The power circuit 206 is connected to and controlled by the control circuit 208 as shown in Figure 4 and more fully described hereinafter.

Referring to Figure 4, depicted is a more detailed schematic block diagram of the control circuit shown in Figure 2, according to the specific example embodiment of this disclosure. The control circuit 208 is connected to the power circuit 206 shown in Figure 3 and comprises a digital processor with memory 462, e.g., microcontroller; high and low switch drivers having deadband logic represented by function block 464, bias generator, current and voltage reference circuits 466; under and over voltage detectors 456, a PWM generator 458, an over current detector 454, a voltage comparison circuit 452, a sensorless inductor current measurement circuit 450, and a communications interface 460. The PWM generator 458 may be of either an analog or digital design for supplying PWM control pulses to the high and low switch drivers 464.

The high and low switch drivers of the function block 464 are coupled to and control when the high and low switches 316 and 318 turn on and off. In addition the deadband logic of the function block 464 prevent the high and low switches 316 and 318 from ever being on at the same time, preferably, there is a deadband where both of the high and low switches 316 and 318 are off. The PWM generator 458 controls when and for how long the power inductor 312 is coupled to and being charged by the power source 320. The boot voltage capacitor 314 supplies power to the high side portion of the switch driver 464; and the bias generator, current and voltage reference circuits 466. The bias generator, current and voltage reference circuits 466 supply precision current and voltage reference values to the current and voltage circuits 452, 454 and 456. The voltage comparison circuit 452 measures the output voltage and compares it to a reference voltage, VREP, from the voltage reference circuit 466. An error signal from the voltage comparison circuit 452, representing the difference between a desired voltage value and the actual output voltage value, is applied to an error input of the PWM generator 458, wherein the PWM generator 458 adjusts its pulse waveform output to minimize that difference (closed loop feedback, see Figure 1). The over current detector 454 monitors the current to the power inductor 312, and the under and over voltage detectors 456 monitor the input voltage to the SMPS for undesirable e.g., abnormal, conditions, e.g., inductor current exceeds allowable design limits, input voltage is above or below a design operating input voltage range. The sensorless inductor current measurement circuit 450 losslessly measures SMPS power inductor current and supplies that measured current value to the PWM generator 458 and the digital processor 462. Operation of the sensorless inductor current measurement circuit 450 is shown in Figure 5 and 6 and more fully described hereinafter.

The sensorless inductor current measurement circuit 450 may be implemented as a matched complimentary filter by utilizing a tunable filter comprising an operational transconductance amplifier (OTA), a variable resistor and a variable capacitor in one specific example embodiment (Figure 5). In another specific example embodiment, an operational amplifier, configured as a buffer, and a variable resistor have been added, providing independent gain and pole location adjustment (Figure 6). The communications interface 460 may be used to communicate with a host system for monitoring operating parameters of the SMPS, e.g., current, voltage, efficiency, operating temperature, diagnostics, etc. In addition, the communications interface 460 may be used to alter the operating parameters (objectives) of the SMPS during operation thereof. Referring to Figure 5, depicted is a schematic diagram of a circuit for losslessly measuring the power inductor current of the SMPS, according to a specific example- embodiment of this disclosure. A tunable complimentary filter inductor current measuring circuit comprises an operational transconductance amplifier (OTA) 522, a variable resistor 524, and a variable capacitor 526. The OTA 522 is configured as a voltage variable integrator and is used as a first-order low-pass filter (see Figures 7 and 8). The transfer function for this integrator is:

v ₀ / (V ₁₁ - v ₁₂ ) = _gri y(s*c ₍ .)

The OTA 522 circuit shown in Figure 5 has an adjustable pole frequency, and adjustable DC gain. The pole frequency is adjusted by the capacitor 526, Cp, and resistor 524, . R and the DC gain is adjusted by the resistor 524, Rp. The transfer function of the filter shown in Figure 5 is represented by:

Vo / (V„ - V ₁₂ ) = (g _m * R _F ) /(s * R _f . * C, + 1 )

As noted from the transfer function, the DC gain is equal to gm * Rp; and the pole frequency is equal to 11(2% * Rp * Cp) Hz. The pole frequency and DC gain can not be adjusted independently.

Referring to Figure 6, depicted is a schematic diagram of a circuit for losslessly measuring the power inductor current of the SMPS, according to another specific example embodiment of this disclosure. A tunable complimentary filter inductor current measuring circuit comprises an operational transconductance amplifier (OTA) 522, a variable resistor 624, an operational amplifier 628 configured as a buffer, a variable resistor 630, and a variable capacitor 526. The OTA 522 is configured as a voltage variable input gain stage with a wide bandwidth. The operational amplifier 628 decouples the input gain stage from the single pole, low pass filter. The pole frequency can be adjusted by changing the resistor 624, Rp, and/or the capacitor 526, Cp, and the DC gain can be subsequently adjusted by changing the variable resistor 630, Ro. The transfer function of the filter shown in Figure 6 is represented by:

Vo (V„ - V ₁₂ ) = (g _m * R ₀ ) /(s * R _F * C _F + 1) As noted from the transfer function, the DC gain is equal to g _m * RG; and the pole frequency is equal to 1/(2π * Rp * Q ) Hz. The pole frequency and DC gain can be adjusted

independently.

The tunable complimentary filters shown in Figures 5 and 6 can be adjusted, e.g., tuned, to match the I VRi. zero, and gain adjusted to amplify the sensed current signal to a desired voltage level. The tunable complimentary filters can further be adjusted in-circuit to significantly reduce the effects of component tolerances. The tunable complimentary filters can be adjusted on the fly in order to adapt to changing operating conditions of the SMPS. The tunable complimentary filters may be used to accurately measure the current through the power inductor 312 for precise closed loop control of the SMPS over all operating conditions so that the SMPS efficiency can be maximized by the digital processor 462 through the PWM generator 458. The sensorless inductor current measurement circuit 450 described hereinabove may also be used to monitor over current through the power inductor, thus taking the place of an eliminating the separate over current detector 454.

' The lossless current measurement circuits shown in Figures 5 and 6, accurately measure current through the SMPS power inductor 312 without wasting power, are highly accurate over all operating conditions, and are flexible and low in cost to implement in a mixed signal integrated circuit 208 (Figure 4).

Referring to Figure 7, depicted is a graph of pole frequency adjustments for the circuits shown in Figures 5 and 6.

Referring to Figure 8, depicted is a graph of DC gain adjustments for the circuits shown in Figures 5 and 6.

Referring to Figure 9, depicted is a schematic block diagram of a mixed signal integrated circuit device for controlling a SMPS system using the specific example embodiments of the tunable complimentary filters shown in Figures 5 and 6. The mixed signal integrated circuit device 902 (e.g., in an integrated circuit package having external electrical connections) comprises a SMPS controller 904, power transistor drivers 906 (e.g., function block 464 of Figure 4), a microcontroller 908 (e.g., digital processor) and associated memory 910 (may be part of the microcontroller 908), an OTA 622, an operational amplifier 728, a DC gain setting resistor 730, a pole frequency setting resistor 624, and a pole frequency setting capacitor 626. The SMPS controller 904 may generate a pulse width modulation (PWM), pulse frequency modulation (PFM), pulse density modulation (PDM), c/c, signal for controlling the power transistor drivers 906 that provide the power control signals to the power MOSFET switches 316 and 318 of the SMPS. The SMPS controller 904 monitors the voltage regulated output voltage, VQUT, and the measured inductor current signal, V ₀ , from the tunable complimentary filter comprising OTA 622, operational amplifier 728, variable resistors 624 and 730, and tuning capacitor 626.

The OTA 622, operational amplifier 728, variable resistors 624 and 730, and tuning capacitor 626 are connected and operate as more fully described hereinabove. The microcontroller 908 may control the variable resistors 624 and 730, as well as setting parameters for the SMPS controller 904 (dotted lines represent control signals). It is contemplated and within the scope of this disclosure that the microcontroller 908 can perform the same functions as and replace the SMPS controller 904. The microcontroller 908 has analog inputs and analog- to-digital conversion circuits (not shown). An operating program for the mixed signal integrated circuit device 902 may be stored in the memory 910 associated with the microcontroller 908. An additional capacitor 626a may be added external to the mixed signal integrated circuit device 902 and in parallel with the internal capacitor 626. The microcontroller 908 may control the capacitance value of the capacitor 626, and in combination with control of the variable resistors 624 and 730. Control of the capacitor 626 and/or variable resistors 624 and 730 by the microcontroller 908 allows dynamic tuning of the gain and/or pole frequency of the tunable complementary filter complimentary filter on the fly for optimal current measurement under changing operating conditions of the SMPS. The tunable complimentary filter implementation(s), according to the teachings of this disclosure can also be applied, but is not limited to, switch-mode power converters (e.g., SMPS), brushless dc motors, etc.

While embodiments of this disclosure have been depicted, described, and are defined by reference to example embodiments of the disclosure, such references do not imply a limitation on the disclosure, and no such limitation is to be inferred. The subject matter disclosed is capable of considerable modification, alteration, and equivalents in form and function, as will occur to those ordinarily skilled in the pertinent art and having the benefit of this disclosure. The depicted and described embodiments of this disclosure are examples only, and are not exhaustive of the scope of the disclosure.