1. Field of the Invention
This invention relates to compensation of feedback systems and, more particularly, to adaptive compensation in digital power controllers.
2. Description of the Related Art
The rapid evolution and increased power consumption of commercial integrated circuits, such as microprocessors and graphics processors, has created new and significant problems in delivery of the power to and removal of waste heat from these ICs. Power supply design is now a much more critical and difficult task than it was a few years ago. High-current/low-voltage ICs require a very clean and stable source of DC power. The power source must be capable of delivering very fast current transients. The electronic path to these loads must also have low resistance and inductance (a 1.5V supply would be completely dropped across a 25 mΩ resistance at 60 Amps).
Traditionally, DC power supplies were designed to convert AC line voltage to one or more DC outputs that would be routed throughout a system to the points of load (POL). However, it may not be practical to route high-current signals throughout a system. To overcome this difficulty, and to reduce the ill effects of distributing high current signals around a system, an alternative method of distributing power at modest voltage and current levels has been adopted. Rather than converting an AC supply voltage level to the DC voltage level required by various loads at a central location, the AC supply voltage is typically converted to a “reasonable” DC voltage and routed to the “point of load” (POL), where it is converted locally to the required low voltage. This technique is referred to as “Distributed Power Architecture”, or DPA.
In many power distribution systems it is typically not enough to just distribute power around a system to the various POLs. Complex electronic systems are generally monitored and controlled to ensure maximum reliability and performance. Functions (power supply features) typically implemented in DPA systems include supply sequencing, hot swap ability, ramp control, voltage programming, load monitoring, tracking, temperature monitoring, fan speed control, phase control, current sharing, switching frequency programmability, and switching clock synchronization, to name a few. There are other functions that may be required for power systems. For example, single points of temperature measurement, open/closed status of doors and vibration may be of interest.
In order to accommodate a demand for more power and denser systems and the resulting new distribution problems, many present power distribution schemes began offering multiples of each solution, or functions, in a single package. Typically each of these functions requires a separate configuration within the system. That is, each function may require its own interconnection network tying the POL converters together. The interconnection network may implement glue-logic that may be required for control of the POL converters in order for the particular function to be successfully executed during system operation. Many of these functions comprise analog signal control requiring corresponding analog signal lines, with POL converters interconnected in point-to-point configurations. Routing of such signals is often difficult, while no true communication is established between various POL converters and/or between the POL converters and any other elements of the system. In an effort to tie all or most of these functions together at the system level, one approach has been to implement the functions in control ICs responsible for controlling respective POL converters. Some of the functionality may also be programmed into a microcontroller that may communicate with attached POL converters over an I2C (inter-IC communication) bus to coordinate control of all POL converters in the system.
DC-to-DC conversion is often performed by switching power regulators, or step-down regulators, converting a higher voltage (e.g. 12V) to a lower value as required by one or more load devices. A common architecture features distribution of the higher voltage to multiple power regulators, each producing a different (or possibly the same) voltage to one or more loads. Switching power regulators often use two or more power transistors to convert energy at one voltage to another voltage. One common example of such a power regulator 100, commonly called a “Buck Regulator” is shown in FIG. 1a. Buck Regulator 100 typically switches a pair of power transistors (108 and 110) in order to produce a square-wave at their common node SW. The produced square-wave can be smoothed out using an LC circuit comprising inductor 112 and capacitor 114 to produce the desired voltage, Vout. A control loop, comprised of an Error Amplifier 116, a Proportional-Integral-Differential (PID) Filter 102, a Pulse-Width-Modulator (PWM) 104, and an Output Control circuit 106, can be configured to control the duty-cycle of the output square-wave, and hence the resulting value of Vout.
For analog control, Type III compensation has typically been a popular choice for compensation of voltage mode switching power supplies. Many types and variations of compensation are available for digital control, but one of the most popular has been digital PID compensation, indicated in FIG. 1a by PID Filter 102, which may be configured to perform digital compensation and/or filtering in Regulator 100. In general, digital power control has been used in various instances in the power industry for some time. As the cost of digital controllers decreases, their increased use becomes more apparent, yet their relative value and advantage over more conventional analog controllers has been a matter of debate. The main question at the center of the debate is whether digital control can truly provide any substantive advantage over analog control.
Semiconductor process technology has developed to the point that digital circuitry definitely has a size advantage over analog circuitry. For example, an entire digital microcontroller may be built to the approximate size of a single (small) analog component: a capacitor. In addition, digital technology offers the potential to integrate and incorporate sophisticated control algorithms, which may simply be too complex, too large, or too expensive to implement as analog designs. An example of this problem is illustrated in “optimized dead time control” or ODTC. ODTC is an innovative search algorithm which adjusts the switching dead times to optimize the efficiency of the power converter. Although analog implementations of “adaptive dead time” have been around for some time, they did not include efficiency optimization but merely the prevention of cross conduction.
Another essential element of power supply operation is stability. Because of the complexity of the system stability under poorly defined (or even poorly understood) load and environmental conditions, compensation for stability may well be one of the areas where digital implementation may provide a decided advantage over analog solutions. Because of the computational efficiency and power of digital control, compensation is an area where digital solutions have a distinct performance advantage over analog implementations.
Many other problems and disadvantages of the prior art will become apparent to one skilled in the art after comparing such prior art with the present invention as described herein.