Electricity: power supply or regulation systems – Output level responsive – Using a three or more terminal semiconductive device as the...
Reexamination Certificate
1998-10-30
2001-03-06
Sterrett, Jeffrey (Department: 2838)
Electricity: power supply or regulation systems
Output level responsive
Using a three or more terminal semiconductive device as the...
C323S283000, C323S284000, C323S285000
Reexamination Certificate
active
06198261
ABSTRACT:
BACKGROUND
The present invention relates generally to voltage regulators, and more particularly to control systems for switching voltage regulators.
Voltage regulators, such as DC to DC converters, are used to provide stable voltage sources for electronic systems. Efficient DC to DC converters are particularly needed for battery management in low power devices, such as laptop notebooks and cellular phones. Switching voltage regulators (or more simply “switching regulators”) are known to be an efficient type of DC to DC converter. A switching regulator generates an output voltage by converting an input DC voltage into a high frequency voltage, and filtering the high frequency voltage to generate the output DC voltage. Typically, the switching regulator includes a switch for alternately coupling and de-coupling an unregulated input DC voltage source, such as a battery, to a load, such as an integrated circuit. An output filter, typically including an inductor and a capacitor, is coupled between the input voltage source and the load to filter the output of the switch and thus provide the output DC voltage. A controller measures an electrical characteristic of the circuit, e.g., the voltage or current passing through the load, and sets the duty cycle of the switch in order to maintain the output DC voltage at a substantially uniform level.
Voltage regulators for microprocessors are subject to ever more stringent performance requirements. One trend is to operate at higher currents, e.g., 35-50 amps. Another trend is to turn on or off different parts of the microprocessor in each cycle in order to conserve power. This requires that the voltage regulator react very quickly to changes in the load, e.g. several nanoseconds to shift from the minimum to the maximum load. Still another trend is to place the voltage regulator close to the microprocessor in order to reduce parasitic capacitance, resistance and/or inductance in the connecting lines and thereby avoid current losses. However, in order to place the voltage regulator close to the microprocessor, the voltage regulator needs to be small and have a convenient form factor.
In addition to these specific trends, high efficiency is generally desirable in order to avoid thermal overload at high loads and to increase battery life in portable systems. Another desirable feature is for the voltage regulator to have a “standby mode” which consumes little power at low loads.
Conventional controllers are constructed from analog circuits, such as resistors, capacitors and op-amps. Unfortunately, analog circuits are expensive and/or difficult to fabricate as integrated circuits. Specifically, special techniques are needed to fabricate resistors and semiconductor devices. In addition, analog signals can be degraded by noise, resulting in a loss of information.
In view of the foregoing, there is room for improvement in voltage regulators and control systems for voltage regulators.
SUMMARY
In general, in a first aspect, the invention is directed to a method of operating a voltage regulator having an input terminal to be coupled to an input voltage source, an output terminal to be coupled to a load, and at least one switching circuit to intermittently couple the input terminal and the output terminal. An estimated current is calculated for each of the at least one switching circuits, each estimated current representing a current passing through an inductor in an associated switching circuit. A desired total output current through the inductors is calculated which will maintain an output voltage at the output terminal at a substantially constant level, and an upper current limit and a lower current limit are calculated. The average of the upper current limit and lower current limit is equal to an individual desired output current for one of the inductors. For one or more of the switching circuits, the switching circuit to is caused couple the input terminal to the output terminal when the estimated current falls below the lower current limit, and caused to couple the output terminal to ground when the estimated current exceeds the upper current limit.
In another aspect, the invention is directed to a method of operating a voltage regulator having an input terminal to be coupled to an input voltage source, an output terminal to be coupled to a load, and at least one switching circuit to intermittently couple the input terminal and the output terminal. An estimated current is determined for each switching circuit, each estimated current representing a current passing through an inductor associated with the switching circuit. A desired total output currentthrough the inductors is calculated which will maintain an output voltage at the output terminal at a substantially constant level. For one or more of the switching circuits, a desired individual current is calculated, and the estimated current is compared to the desired individual current to cause the switching circuit to switch so that the current flowing through the switching circuit is approximately equal to the desired current.
In another aspect, the invention is directed to a method of operating a voltage regulator having an input terminal to be coupled to an input voltage source, an output terminal to be coupled to a load, and a plurality of switching circuits to intermittently couple the input terminal and the output terminal. One of the plurality of switching circuits is selected as a reference circuit, and a desired phase offset is determined for the remaining switching circuits. An estimated current is calculated for each switching circuit, each estimated current representing a current passing through an inductor associated with the switching circuit. A desired total output current through the inductors is calculated which will maintain an output voltage at the output terminal at a substantially constant level, and the switching circuits are caused to couple the output terminal to the input terminal or to ground in a manner so as to substantially achieve the desired phase offsets and the desired total output current.
Advantages of the invention may include the following. The voltage regulator handles relatively large currents reacts quickly to changes in the load. The voltage regulator may use small capacitors with a convenient form factor. The voltage regulator can include multiple slaves which are operated out of phase in order to reduce current ripple. The use of analog circuits is minimized by converting analog measurements in the controller into digital signals. The controller may be implemented using mostly digital circuitry, and may be fabricated using known processes through conventional complementary metal oxide semiconductor (CMOS) fabrication techniques. This reduces the number of off-chip components in the controller. The controller operates with a digital control algorithm in which the operating parameters may be modified to adapt the voltage regulator for different applications. The digital control algorithm can operate at clock frequency significantly higher than the switching frequency, allowing quick response to changes in the load. The master and slaves can communicate with digital signals, thereby providing improved communication reliability.
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Burstein Andrew J.
Christenson Michael
Schultz Aaron
Fish & Richardson P.C.
Sterrett Jeffrey
Volterra Semiconductor Corporation
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